1998 Walton

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Journal of the Neurological Sciences 158 (1998) 514

1Decade of the brain: neurological advances

Lord Walton of Detchant

President, World Federation of Neurology, Oxford OX2 6PS, England

Received 30 September 1997; accepted 26 November 1997

Abstract

In the last half century, neurological developments have been phenomenal and have escalated in this decade of the brain. Many

infective disorders have been conquered, but AIDS has posed new challenges. Neuropharmacology has transformed the management of

parkinsonism and epilepsy. New imaging techniques such as CT, NMR, PET and ultrasonic scanning have presented us with remarkable

images of the nervous system in health and disease. Steroids control many autoimmune disorders; beta-interferon and other new drugs

have begun to influence multiple sclerosis. Intensive care has saved many of those with head injury or acute neurological disorders, and

we have greatly improved methods of rehabilitation. There are still many incurable neurological disorders but none are untreatable.

Todays discovery in basic science brings tomorrows improvement in patient care, as is clearly shown by molecular genetics. Some

neurological and neuromuscular diseases in which the causal gene or genes have been located and characterised and in which the missing

or abnormal gene product has been identified will be mentioned, as well as the prospects of carrier detection, antenatal diagnosis and gene

therapy. 1998 Elsevier Science B.V.

1. Introduction 2. Clinical neuroscience: a quarter century of

progress

In this my final year as President of the World Federa-

tion of Neurology, and in the seventh year of the Decade The conquest of many once devastating infective dis-

of the Brain, I regard it as a singular honour and privilege orders such as poliomyelitis and smallpox is now largely a

to have been invited to give this plenary lecture and to matter of history, but as new antibiotics and vaccines have

attempt to highlight some of the major advances in our been discovered, so nature has posed new challenges.

discipline which have been made possible by develop- AIDS, which may seriously damage the nervous and

ments in neuroscience during my professional lifetime (of neuromuscular systems, represents one such infective

now some 52 years) and which are likely to yet further disorder which presents the medical profession with yettransform our understanding of neurological disorders well another difficult mountain to climb, but combinations of

into the next millennium. And may I, at the outset, express new antiviral agents bring hope for the future. Stroke,

my personal sincere gratitude first to our Argentinean hosts especially ischaemic stroke, continues to be a major killer

for the excellence of their planning and organisation and to and crippler [1]. Most advances have related to prevention,

the officers, chairmen and members of committees and as relatively little can be done once the stroke occurs.

delegates of the WFN who have given me such unfailing Trials of remedies such as calcium antagonists or tissue-

support over the last eight years. type plasminogen activator have shown only marginal

benefit in acute stroke. However, prevention by treatment

with aspirin in patients suffering transient ischaemic1 attacks, or by carotid endarterectomy in individuals withThe inaugural lecture, delivered at the XVI World Congress of Neurolo-gy, Buenos Aires, Argentina, September 1997. suitably severe degrees of carotid stenosis [2] have each

0022-510X/98/$19.00 1998 Elsevier Science B.V. All rights reserved.

P I I : S 0 0 2 2 - 51 0 X ( 9 7 ) 0 0 3 17 - 1

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6 Lord Walton of Detchant / Journal of the Neurological Sciences 158 (1998) 514

constituted major advances. Perhaps above all, new tech- 3. Molecular genetics and neurological disease

niques of imaging, including CT, NMR and PET scanning

and the use of sophisticated ultrasonic techniques including 3.1. Gene mapping

the Doppler method, have presented us with images of the

nervous system and of the effects of pathological processes As mapping of the human genome (the HUGO project)

upon it undreamt of only a few years ago [3]. And NMR proceeds apace through international collaborative effort,

spectroscopy has given invaluable information about meta- we learn almost monthly that yet another gene has been

bolic changes in brain and muscle in health and disease. located, and many have been fully characterised and

While many such techniques are expensive, both in capital sequenced. A table published in Neuromuscular Disorders

and in revenue costs, the benefit to patients and the (Vol. 6, No. 5, 1996) presents, by way of example, a

avoidance of the suffering resulting from older methods selective list of some important neuromuscular disorders in

such as pneumoencephalography and ventriculography which gene mapping has been achieved within the last few

have outweighed the cost to society if assessed in both years. In relatively few do we yet know the nature of the

financial and social terms. Interventional neuroradiology missing or abnormal gene product. However, in some

has much more to give, not least in the treatment of recessively inherited disorders, gene deletions or point

intracranial aneurysms, and advanced clinical neuro- mutations clearly result in the absence of an important

physiological techniques have also enhanced our diagnos- structural protein, while, by contrast, in some autosomal

tic capability. New and improved methods of intensive dominant conditions (such as myotonic dystrophy, Hunting-

care have saved many who would formerly have died from tons chorea and various cerebellar ataxias including

head injury or severe paralysing disorders. The identifica- MachadoJoseph disease) there are abnormal nucleotidetion of new neurotransmitters, along with neurophar- triplet repeats, whose extent can often be correlated with

macological and neurochemical research, has led to the age of onset and disease severity. These discoveries are

introduction of many new drugs, including increasingly inevitably taking us further towards identifying the ulti-

effective anticonvulsants [4,5], while steroids, plas- mate cause of many such disorders and we may anticipate

mapheresis and other immunological techniques have that in some, effective treatment will soon be devised,

proved beneficial in many autoimmune disorders of the either through gene therapy or through some other means,

muscular and neuromuscular systems. such as cell transplantation, of circumventing the genetic

Pain relief has been transformed and we have available defect. The subject has been reviewed by Yates [6], Hurko

much improved techniques of rehabilitating patients recov- [7], Joynt and Kurlan [8] and Sharma and Baynes [9].

ering from acute neurological illness and of improving the

lifestyle and longevity of many with progressive and as yet

incurable conditions. The range of new appliances and of 4. Alzheimers disease and some other dementiasphysical and communication aids developed by bioen-

gineering expertise is striking. In neurology there are still As knowledge accumulates, it is increasingly clear that

many incurable diseases but none are untreatable. All can Alzheimers disease, whether occurring in the presenium

have their effects modified by pharmacological, physical or or in the senium, is not a single entity [10]. And diffuse

psychological intervention. Lewy body dementia, with or without clinical evidence of

There is another incontrovertible truism which sadly Parkinsonism, may closely mimic the condition, as may

does not always convince health care providers and/ or the rare familial dementia due to a frameshift in the

research funding agencies. It is that todays discovery in caeruloplasmin gene [11]. Diagnosis from multi-infarct

basic laboratory science brings tomorrows practical de- dementia can usually be achieved by scanning, but distinc-

velopment in patient care. In no field is this more evident tion from other dementias, including the frontal lobe type,

than in molecular biology and molecular genetics and in is more difficult in the absence of a specific marker.

the burgeoning area of gene therapy. As it would be Hence, despite the increasing use of NMR and PET

impossible to highlight in this talk even the major develop- imaging, along with refined psychometric tests, clinicalments in all these sciences which are influencing clinical diagnosis remains imprecise and is probably correct in no

practice, I must be selective. more than 85 90% of cases of dementia. This may have

I therefore propose to mention first some neurological prejudiced conclusions drawn from some epidemiological

disorders in which the causal gene has been located and its studies based upon clinical diagnosis. Nevertheless, knowl-

effects identified, secondly to comment upon new knowledge of pathogenesis is accumulating apace. It is agreed

edge relating to dementia, especially to Alzheimers dis- that the histological hallmarks of the disease are neuro-

ease, and thirdly to refer briefly to new developments in fibrillary tangles and senile plaques in the cerebral cortex.

multiple sclerosis and some other neurological disorders. Tomlinson et al. [12,13] found similar but less severe

Finally, I shall turn to exciting developments in neuro- changes in brains of nondemented elderly people and also

muscular disease, with particular reference to the inflam- defined a quantitative relationship between the severity of

matory myopathies and to the muscular dystrophies. dementia and the numerical incidence of these changes.

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Lord Walton of Detchant / Journal of the Neurological Sciences 158 (1998) 514 7

Later, Bowen et al. [14] and Perry et al. [15] showed that of several different viruses, triggers an autoimmune pro-

acetylcholine and choline acetyltransferase activity were cess. Myelin-reactive T cells then act upon the myelin in

markedly reduced in the cerebral cortex. It was later shown the central nervous system but also increase the per-

that paired helical filaments in the plaques are associated meability of the blood / brain barrier, leading to perivascu-

with hyperphosphorylated tau protein [16]. lar inflammatory cell infiltration which in turn increases

The senile plaques in amyloid disease contain an the extent of the demyelination. However, treatment of the

amyloid b-protein, the so-called A4 protein or b A4 disease with steroids, with intravenous immunoglobulin

peptide. From its primary amino acid sequence, the cDNA and with immunosuppressive agents such as azathioprine

clone has been isolated and has been shown to encode for has given disappointing results.

a much larger 770 amino acid protein called the amyloid Among the new drugs recently introduced in treatment

precursor protein (APP) of which six transcripts have been have been interferon beta-1a and beta-1b, of which the

isolated, four containing the b A4 moiety. The physiologi- latter has seemed marginally more effective [31,32], but

cal role of APP in the brain is as yet unclear but is the recent reports have favoured beta-1a. Interferon alpha-2a

subject of intensive research [17]. Recent research has also has also been tested but does not seem to confer any

indicated that APP expression is abnormal in head injury lasting benefit [33]. Useful guidelines covering the use of

and stroke, in which the release of interleukin 1 may lead the interferons have now been published [34] and despite

to progressive cell stress. published reservations about the cost-effectiveness of these

In familial Alzheimers disease, responsible genes, also remedies [35], their value in reducing relapses in remit-

related to the genetic abnormality in Downs syndrome, tingrelapsing disease is now amply confirmed [36].

were identified on chromosome 21 in both exons 7 and 17 Another new agent, copolymer 1, is a synthetic poly-[18,19]. In early-onset Alzheimers disease, however, there peptide consisting of L-alanine, L-glutamic acid, L-lysine

is evidence that other genes lie on chromosomes 1 and 14; and L-tyrosine. It is thought to work either by producing

that on chromosome 14, called presenilin-1 (PS-1), associ- antigen-suppressor cells specific for myelin basic protein,

ated with 5 missense mutations (amino acid substitutions), or more probably by interfering with T-cell activation by

is now known to account for about 70% of early-onset competing with myelin basic protein for the major his-

familial cases [6]. It has also been shown that apolipo- tocompatibility complex class 2 binding sites responsible

protein E (apoE4) homozygotes carry a high risk of for antigen presentation. In a study of the effects of this

developing Alzheimers disease relatively early in life, remedy by Johnson and others [37] the relapse rate was cut

whereas those who are homozygous for apoE3 are more by 24%, and the percentage of patients who developed

likely to develop the condition later. While the use of the worsening neurological disability was also reduced in a

apoE4 marker in genetic counselling and in diagnosis was randomised, double-blind, placebo-controlled trial involv-

once postulated, its relationship to the disease is not ing 251 patients.precise enough, especially since recent work has suggested Linomide, a synthetic immunomodulator that increases

a possible relationship between apoE4 and Lewy body natural killer cell activity, has also been used [38,39] but it

disease and also frontal lobe dementia [2022]. produces unacceptable side-effects. The potential value of

In therapy, choline, lecithin, eserine, tacrine, donepezil the chimeric anti-CD4 antibody is as yet unconfirmed.

and rivastigmine have all been tried, the latter three

remedies proving effective in delaying progression of the

disease to some extent [2325]. But the cost effectiveness 6. Some other neurological disorders

of such treatment has been questioned [26]. Work is now

proceeding to examine the role of acetyl-L-carnitine [27] 6.1. Neurotransmitters

and of free radical scavengers. Nerve growth factors such

as brain-derived neurotrophic factor (BDNF) and Nitric oxide (NO), the molecule of the decade, has now

neurotrophin-3 (r1 T-3) are also being studied, as are drugs been shown to be a neurotransmitter [40]. Relaxation of

which stimulate nicotinic receptors or others which inhibit arterial muscle is brought about by several messengerb A4 peptide enzymes and calcium entry. Even antiinflam- molecules, one of which is acetylcholine. It had always

matory remedies such as indomethacin and other NSAIDS been thought that acetylcholine in the blood acted directly

may have a protective effect or may confer marginal upon muscle cells, causing relaxation, but in the 1980s

benefit [23,28]. acetylcholine was shown to release an endothelium-derived

relaxing factor from the endothelium of blood vessels; this

was eventually identified as nitric oxide, which diffuses

5. Multiple sclerosis into the surrounding muscle in the arterial wall and triggers

muscle relaxation. Glyceryl trinitrate, the vasodilator, is

It is now agreed [29,30] that in multiple sclerosis (MS) transformed into nitric oxide in the body. The role of nitric

there is an underlying genetic susceptibility. Against such oxide has also proved to be very much more ubiquitous

a background an environmental factor, which may be one than originally thought.

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It is involved in stimulation of macrophages dealing 6.2. Cytokines

with infection and has an important role in type 1 diabetes,

in septic shock, in arming the immune system, in prevent- Much interest has also been aroused by recent work on

ing premature birth, and in treating impotence. There is cytokines, a heterogeneous group of polypeptide mediators

also good evidence emerging to indicate that as a neuro- or intercellular messengers, classically associated with

transmitter it may play a part in the control of memory. activation of the immune system and inflammatory re-

Indeed NO as a diffusible messenger is long-lasting, sponses. They include the interleukins and interferons and

playing an important role in modulating neuronal firing it is clear that this class of substances plays an important

behaviour and being involved in synaptic plasticity. NO role in providing communication signals between the

synthase (NOS) is a regulator of cerebral blood flow and immune system and the brain. Their role in neurological

NO appears to be involved in learning, pain, sleep, feeding disease and dysfunction will surely be further clarified in

and sexual function [41]. the next century, but it is already evident that cytokine-

Of equal interest and importance is the fact that excitat- based treatment, as with the interleukins and interferons,

ory amino acid systems are of fundamental importance in will be invaluable in treating inflammatory, immune and

the pathogenesis of several neurological diseases [42,43]. infective conditions [44].

In particular, glutamate is the predominant excitatory

transmitter in mammals, acting upon at least four major 6.3. Parkinsonism and motor neurone disease

subtypes of receptor, namely the NMDA, AMPA and

kainate ( KA) receptors, and also metabotropic receptors, In Parkinsonism, as in ischaemia and stroke, free radical

upon which I shall not comment further. However, AMPA production or defective antioxidation involving glutathionereceptors are responsible for much of the fast excitatory may contribute to nigral cell death. Studies reported in the

neurotransmission in the nervous system and several last 3 months have located the gene for familial Parkinson-

selective antagonists for the AMPA receptor have been ism on chromosome 4 [45]. Ubiquitin staining, which is

developed. The NMDA receptors are more complex, and positive in the nigral cells and in cells throughout the

the KA receptors are as yet not well understood, though cortex in patients with Lewy body dementia, indicates

they have a high affinity for kainate, an analogue of protein degradation. Annual crude death rates from Parkin-

glutamate. Glutamate is clearly an excitotoxin and it seems sons disease in Norway confirm the increased survival of

that a relative excess of this substance can under certain individuals since levodopa was introduced [46]. Some

circumstances contribute to neuronal death in Huntingtons evidence suggested that selegiline as an initial treatment in

disease, Alzheimers disease, Parkinsons disease and do novo parkinsonian patients might be effective and

amyotrophic lateral sclerosis. Clearly, too, glutamate plays might delay the necessity for giving levodopa [47], and

a fundamental role in epilepsy; glutamate receptor antago- indeed it was thought earlier that selegiline might exert anists are powerful anticonvulsants, but they also appear to neuroprotective action and prolong longevity. However,

reduce brain damage after ischaemia and trauma in animal recent work [48,49] has failed to demonstrate any such

models. This is because, as an excitotoxin, glutamate may effect. Experimental studies using glial-derived neuro-

contribute to cellular calcium overload, to increased lipid trophic factor (GDNF) in MPTP-induced Parkinsonism in

peroxidation and to the release of free radicals. There is animals have raised the possibility of using this preparation

also growing evidence to indicate that oxidative stress due in human subjects.

to increased free radical production and/ or defective Ubiquitin, despite being indicative of protein degra-

antioxidant defences (as with superoxide dismutase in dation, has been discovered in normal motor end-plates in

familial amyotrophic lateral sclerosis and glutathione in the postjunctional region. However, it accumulates in

Parkinsons disease) may be central to some neurode- excess in anterior horn cells in cases of motor neurone

generative processes. All of this evidence has raised the disease and in these neurones there is increased activity of

possibility of new forms of treatment being introduced, not proline endopeptidase and pyroglutamyl aminopeptidase

only for ischaemia, stroke, epilepsy and head injury, but [50]. In familial cases of this condition there is evidence ofalso perhaps for some of the neurodegenerative diseases an altered encoding of copper / zinc / magnesium-controlled

which I have mentioned. superoxide dismutase and the gene responsible has been

Calcium antagonists have been shown to have limited localised to chromosome 21q [3]. There is now evidence

benefit in limiting ischaemic damage, and free radical that the apoE2/ 3 genotypes may be protective, while

scavengers have also been tried, though the commonest of apoE4 is associated with earlier onset, bulbar involvement

these, namely vitamin E and ascorbic acid, do not seem and greater severity [51].

very effective. However, work is now in progress upon the A possible role of glutamate in motor neurone disease

role of NMDA and AMPA receptor antagonists. Glutamate has been postulated, though glutamate antagonists such as

antagonists such as lamotrigine are clearly effective in lamotrigine have not been shown to be of any benefit and

treating epilepsy. nor have an array of antioxidants [52]. However, trials of

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riluzole, which modulates glutamate transmission, suggest into proteins, leading to the formation of insoluble

that this remedy may be of some benefit in cases present- proteinaceous aggregates. An abnormal protein called

ing with bulbar involvement, but this remains to be huntingtin has been found to be widespread throughout the

confirmed. Recent work has suggested that neurotrophin-3 brain in affected individuals. A huntingtin-associated pro-

or ciliary neurotrophic factor may ultimately prove to be of tein (HAP-1) has also been identified and may prove to be

benefit. a target for future experimental therapy. In the meantime,

preliminary work which could lead to treatment with

6.4. The stiff-man syndrome transplanted fetal caudate neurones is in progress. And

work done in France and the USA and reported in Nature

Another interesting finding is the recent discovery that in March 1997 has suggested that human ciliary neuro-

the stiff-man syndrome, a rare disorder of unknown trophic factor, delivered by intrastriatal implants of ge-

aetiology in which progressive rigidity, spasms and con- netically modified hamster cells encapsulated in porous

tinuous motor activity occurs, may be due to dysfunction membranes may produce clinical improvement.

of GABAergic inhibition of alpha motor neurones. Au-

toantibodies to GABAergic neurones have been identified

in some cases and the condition is believed to be au-

toimmune, responding to treatment by plasmapheresis [53]. 7. Neuromuscular disease

6.5. Creutzfeldt Jakob disease 7.1. Myotonic dystrophy

In CreutzfeldtJakob disease, which is associated with The mutation causing myotonic dystrophy is an unstable

an isoform of the host-encoded prion protein [54], it is now CTG trinucleotide repeat in a gene at chromosome 19p

clear that not only is the condition closely related to the 13.3 which encodes for a protein with putative serine

autosomal dominant GerstmannStrausslerScheinker threonine kinase activity [62]. The number of repeats

syndrome, but that genetic factors influence susceptibility correlates with the severity and age of onset of the disease,

to the disease and also its duration, age of onset, clinical early onset being related to a larger number. No such

signs and clinical presentation, as well as the distribution repeats are found, however, in the rare proximal myotonic

and type of lesions in both sporadic and familial CJD [55]. myopathic syndrome for which no gene location has yet

The relevant gene (or genes) lie on the short arm of been identified [63]. The finding of pathological tau

chromosome 20 and 12 point mutations have been iden- proteins, tau 55, 64 and 69, in the brains of patients with

tified especially at codons 102, 117, 178 and 200. The myotonic dystrophy is reminiscent of certain features of

so-called new variant, which may be related to bovine Alzheimers disease [62].spongiform encephalopathy (BSE), is associated with

methionine homozygosity at codon 129 [56,57]. The

closely related condition of familial fatal insomnia has 7.2. Myositis pathogenesis and therapeutic trials

been found to be related to a polymorphism at codon 129

[58]. Mutations have also been identified in a group af The role of T-cell mediated cytotoxicity in polymyositis

Libyan Jews who are highly susceptible to this disease and of an autoimmune, humoral vasculopathy in dermato-

[59]; it was once thought that this was because they ate myositis are now fully accepted [6466]. No single virus

sheeps eyes as a delicacy and hence might have been or other infective agent has been shown to be consistently

infected by the scrapie agent, but this is now known not to responsible for initiating the autoimmune process but the

be so as a substitution of lysine for glutamate has been part played by HTLV-1 [67] seems to be of growing

found in codon 200. And of great interest is that the apoE4 importance, while HIV also accounts for a few cases.

marker is an important risk factor relating to the develop- In patients who are resistant to corticosteroids, many

ment of CreutzfeldtJakob disease, as it is in Alzheimers other forms of treatment are available for both poly-disease [60] and perhaps in Parkinsonism and Lewy body myositis and dermatomyositis and for related conditions

disease [61]. such as sarcoid, granulomatous myositis and localised

nodular myositis. They include other immunosuppressive

6.6. Huntingtons disease drugs, plasmapheresis (in dermatomyositis) or total body

irradiation. Immunomodulatory therapy with intravenous

Since the gene for Huntingtons chorea was identified on immunoglobulins has been shown to be useful [68,69] but

chromosome 4.16.3 in 1993, it was found that the mutation because of side-effects, fortunately few of which are

causes an unstable cytosineadenineguanine (CAG) tri- serious [70], it cannot be tolerated by all patients; hence its

nucleotide repeat. It appears that the abnormal triplet place in treatment is still to be defined [69] and it is still

repeat causes excessive glutamine residues to be inserted very expensive.

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7.3. Inclusion body myositis sequential variable deficiency of laminin-a2 [78,79]. Pre-

natal diagnosis by studying laminin-a2 chain expression in

Previous work suggesting a possible role of the mumps trophoblast samples obtained by chorionic villus sampling

virus in the aetiology of this condition has not been is now possible [80].

confirmed and no causal virus has been isolated. However, These are but a few of the manifold discoveries which

Askanas, Engel and others [71,72] demonstrated ubiquitin are being made almost daily by scientific endeavour in

in the postjunctional area of the end-plates of normal these disorders, discoveries which already contribute to

human individuals and also found it in the filaments and improved management of patients and families and which

microtubules associated with the vacuoles and inclusions will surely lead to more effective treatment in the future.

in inclusion body myositis. They also identified amyloid,

prion-related protein, phosphorylated tau, b-amyloid pro- 7.5. Duchenne and Becker muscular dystrophy

tein, a-antichymotrypsin and apoE4 immunoreactive de-

posits. This interesting finding postulates a curious rela- In my former research laboratories in Newcastle upon

tionship between this disorder of muscle on the one hand Tyne, a major breakthrough came in 1975 when Cullen

and Alzheimers disease on the other. Clearly there is a and Fulthorpe [81], using electron microscopy, studied the

link here which must be further explored. Unfortunately, earliest structural changes occurring in the muscle fibres of

immunosuppressive therapy produces little or no benefit in patients with preclinical Duchenne dystrophy. Under

this condition and despite one or two promising prelimin- phase-contrast illumination, in unfixed muscle fibres they

ary reports about the value of IVIgG, the effects of this found multiple contraction bands which were clearly

remedy are still uncertain [73]. responsible for fibre hyalinisation. In plastic-embeddedfibres stained with toluidine blue, these areas might be very

7.4. Emery Dreifuss, facioscapulohumeral, limb-girdle localised, involving only a small segment of a fibre in

and congenital muscular dystrophies transverse section, usually adjacent to the sarcolemma;

they and Bradley also found a marked excess of calcium in

While much international interest has been aroused by these areas.

work on the Duchenne and Becker type muscular They concluded that in Duchenne dystrophy there was

dystrophies upon which I shall concentrate in the conclud- probably a defect in the plasma membrane allowing the

ing section of my lecture, developments in knowledge of ingress of calcium from the extracellular space, which

the other muscular dystrophies has been no less striking. activated calcium-activated neutral proteases which then

Thus in the relatively benign form of muscular dystrophy led to the breakdown and digestion of muscle fibres.

with progressive contractures called the EmeryDreifuss Pennington [82] confirmed that such calcium-activated

type, due to a mutation on the long arm of the X- proteases were present in excess. Almost simultaneouslychromosome, the missing protein, now called emerin, has Mokri and Engel [83], also using electron microscopy,

been identified and, as it is very much smaller than demonstrated focal defects in the plasma membrane which

dystrophin, the missing protein in Duchenne dystrophy, the they called the delta lesion.

prospect of gene therapy in the future will clearly arise. In But the greatest impetus to research came from molecu-

autosomal dominant facioscapulohumeral (FSH) dystrophy lar biology. In 1987, through work in many laboratories,

the gene has been mapped to chromosome 4q35; a including some in Holland, Toronto and Oxford to name

polymorphic fragment is made up of D424 (3.3 Kb) but three, but ultimately through the energy, industry and

tandem repeats. It probably does not encode a protein with expertise of Drs Kunkel, Hoffman and their colleagues at

any direct association with FSHD but there is a clear the Boston Childrens Hospital, the gene for Duchenne

correlation between the size of deletions at this locus on muscular dystrophy was finally isolated, localised and

the one hand and age of onset of the disease on the other characterised in the Xp 21 region of the female X-chromo-

[74]. some. It has proved to be one of the largest genes known

The situation in respect of limb-girdle dystrophy in human genetics with a length of about 2 megabases(LGMD) is even more complicated as about seven sub- [84,85]. Furthermore, the genes for Duchenne and Becker

varieties have been recognised, related to at least five dystrophy are allelic, clinical expression depending, at

genes lying on chromosomes 2, 5, 13, 15 and 17 [75]. least in part, upon the number and extent of the deletions

Many appear to be due to deficiency of specific sar- within the gene. This gave us a much more precise and

coglycans, glycoproteins which bind dystrophin; thus accurate means of identifying the female carriers of these

adhalin is deficient in LGMD2D, calpain 3 in LGMD2A X-linked genes in most affected families. It also led to

[76]. accurate antenatal diagnosis of both affected Duchenne

It has also been discovered that one form of congenital boys and of female carriers, through chorionic villus

muscular dystrophy is due to a deficiency of merosin, sampling to which I shall refer again.

causing disruption of the muscle basal lamina [77] and that Identification of the gene led to isolation of the missing

a variable clinical phenotype may be dependent on con- gene product, namely dystrophin [85] which is totally

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absent in almost all cases of Duchenne dystrophy and ing relatively little immune response and proving more

much reduced in the Becker variety. Further work showed advantageous than other adenoviruses or naked plasmid

that dystrophin is a vital structural component of the DNA [96].

plasma membrane of the skeletal muscle fibre [86]; it thus An alternative possibility may in future be the prospect

appears that the earlier observations of Cullen, Fulthorpe, of upregulating utrophin, a normal constituent of the

Mokri and Engel upon the pathogenesis of muscle fibre muscle fibre membrane, present in Duchenne boys but

breakdown have been largely vindicated. The absence of localised in them, as in normal subjects, in the region of

dystrophin renders the plasma membrane incompetent and the neuromuscular junction. It is believed that if this

leads on to the breakdown process which I have outlined protein could be upregulated and encouraged to diffuse

[87]. There is some evidence that long-term treatment with along the sarcolemma, it might, at least in part, replace the

prednisone or prednisolone may slow down this break- missing dystrophin [97]. Prof. Kay Davies of Oxford is

down process a little, but because of side-effects, relatively leading these studies. I firmly believe we shall have an

few neurologists recommend this as a routine treatment. effective treatment within 10 years.

Much research is now concentrating upon methods of In the meantime, however, there is a prospect of

attempting to repair the membrane defect by means of prevention of Duchenne dystrophy through embryo re-

gene therapy in affected children identified at birth. search. Carrier detection, as already mentioned, is 9598%

Fortunately, a naturally-occurring X-linked muscular accurate in informative families. Such carriers in the past

dystrophy has been identified in the mdx mouse [88] and could only be advised that if they fell pregnant, they

yet another in strains of golden retrievers and rottweilers should undergo amniocentesis at the fourteenth week and

[89]. These afflictions are in many respects comparable to then have an abortion if the fetus was male. Now, withthe human disease. The Duchenne gene transcript is chorionic cell biopsy at eight or nine weeks, it is possible

lacking [90] and dystrophin is absent from the muscle cells not only to sex the unborn fetus but, using current

of affected animals. Cardiomyopathy like that of Duchenne molecular biological techniques, to demonstrate whether or

dystrophy occurs in the dogs [91] and in carriers of the not, in a male, the abnormal gene is present. And now [98]

X-linked canine disorder mosaic expression of dystrophin prenatal diagnosis can even be achieved using a single

comparable to that found in the muscle of human female nucleated erythrocyte obtained from maternal blood.

carriers has been found [92]. Experiments in gene replace- Hence selective abortion of affected males is now feasible.

ment are being undertaken in such animals. While myo- Even though chorionic cell biopsy does carry limited

blast transfer [93] has been found to restore dystrophin clinical risks [99], most carriers regard these as acceptable.

partially and temporarily in dystrophic mice, this technique Of even greater importance is the fact that in vitro

has not proved helpful in human subjects [1,94]. fertilisation and pre-embryo biopsy is now likely soon to

A new dimension was added through the work of Acsadi make preimplantation diagnosis possible. The Humanand others in 1991 [95]. Previous studies had shown that Fertilisation and Embryology Act, which received the

after pure plasmid DNA was injected into rodent muscle, royal assent after its final passage through both Houses of

the cells expressed reporter genes. They showed that a Parliament in the UK in 1990, allows research on the

12-kb full-length human dystrophin cDNA gene and a human embryo up to 14 days after fertilisation. Without

6.3-kb Becker-like gene could be expressed in cultured this Act, and the establishment of a Human Fertilisation

cells and in vivo. When the human dystrophin expression and Embryology Authority to license such work, all

plasmids were injected intramuscularly into dystrophin- research of vital importance to the infertile and to carriers

deficient mdx mice, the human dystrophin proteins per- of the gene responsible for Duchenne dystrophy and those

sisted in the cytoplasm and sarcolemma of myofibres. causing many other crippling inherited disorders would

Those myofibres expressing human dystrophin contained have been prevented by law.

an increased percentage of peripheral nuclei. Since then, When several female ova, released into the uterus at the

work exploring the potential prospects of gene therapy has time of ovulation, are fertilised by sperm, the process of

moved forward rapidly. Miniconstructs of the dystrophin cell division begins and within the first few days floatinggene have been prepared and a variety of different (mainly free in the uterus are 4 to 6 groups of undifferentiated but

viral) vectors to which such constructs can be spliced have pluripotential cells, each forming what I prefer to call a

been prepared; the hope is that if problems of immune conceptus or a pre-embryo rather than an embryo. The

rejection can be overcome, such vectors can be used to term pluripotential means that it is impossible at first to

carry the minidystrophin gene into the muscle cells identify which cells will form the membranes and placenta

throughout the body. In Becker dystrophy, unlike the and which will later form an identifiable embryo from

Duchenne type, rejection of the dystrophin construct which a fetus will develop. By about the fourth or fifth

should not arise as small amounts are normally present in day, the conceptus becomes a blastocyst [100] in which

the muscle. Both retroviruses and adenoviruses have been there is a nodule or cluster of cells called the inner cell

used; at present it seems that adeno-associated virus (AAV) mass from which the embryo later derives, and an outer

vectors from the human parvovirus are favoured, produc- ring of cells which will form the membranes and the

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placenta. But no such blastocyst is yet attached to, or doubt, in the next millennium further developments in this

embedded in the wall of the uterus and about 80% of them rapidly evolving field will bring new hope to many of our

are spontaneously aborted. About one in five begins to patients. At last they will see increasing prospects of new

attach to the uterine wall at about the seventh day, and effective treatments being introduced for some of

subsequently receiving a blood supply from the maternal those progressive and disabling neurological disorders

circulation; later, at about the fourteenth day, that specific which are at present incurable. As my Presidency of the

linear arrangement of cells within the basal cell mass World Federation of Neurology draws to a close, I am

which constitutes the primitive streak appears. confident that the future of our specialty could not possibly

Work done in the last few years by Prof. (now Lord) be more exciting.

Winston at Hammersmith and by others has shown that it

is now feasible, without damage to subsequent develop-

ment of the embryo, to carry out blastocyst biopsy after in Referencesvitro fertilisation by removal of a single cell at about the

fourth or fifth day; that single cell can now be removed [1] Joynt RJ. Neurology. J Am Med Assoc 1996;275:18267.from the part which will form the membranes and the [2] North American Symptomatic Carotid Endarterectomy Trial Col-

laborators. Beneficial effect of carotid endarterectomy in symptom-placenta. Sexing of the conceptus is now commonlyatic patients with high-grade carotid stenosis. New Engl J Medperformed and Professor Winston and his colleagues have1991;325:44553.found it possible to identify in single cells not only the sex

[3] Howard RS. Neurology: recent advances. Br Med J 1994;309:382of the conceptus but also whether or not various disease 95.

genes (such as that for cystic fibrosis) are present. As yet, [4] Marson AG, Kadir ZA, Chadwick DW. New antiepileptic drugs: asystematic review of their efficacy and tolerability. Br Med Jthe size of the Duchenne gene has made it difficult to1996;313:116974.achieve preimplantation diagnosis of this disease, but this

[5] Walker MC, Li LM, Sander JWAS. Long term use of lamotriginewill surely soon be possible. This will make it feasible forand vigabatrin in severe refractory epilepsy: audit of outcome. Br

such carrier women to have normal sons and non-carrierMed J 1996;313:11845.

daughters, a prospect undreamed of a few years ago. [6] Yates JRW. Medical genetics: recent advances. Br Med JI understand and appreciate the sincerity of those who 1996;312:10215.

[7] Hurko O. The explosion of neurogenetics. Curr Opinion Neurolbelieve that human life begins at conception and that any1997;10:7783.experiment on what they regard as a human life, or what

[8] Joynt RJ, Kurlan RM. Neurology. J Am Med Assoccan become one, is to them abhorrent. I am, however,

1997;277:18734.personally satisfied, as are many eminent theologians [9] Sharma P, Baynes K. Molecular medicine: from laboratory toincluding the former Archbishop of York, Lord Soper, the clinical practice. J Royal College Phys London 1997;31:32831.

[10] Rapoport SI, Pettigrew KD, Schapiro MB. Discordance and con-

Rev. Prof. Gordon Dunstan and the Rev. Dr Norman Ford, cordance of dementia of the Alzheimer type (DAT) in monozygotica distinguished Australian Roman Catholic theologiantwins indicate heritable and sporadic forrms of Alzheimers disease.

[101] that individuation of the human embryo does notNeurology 1991;41:154953.

begin until the primitive streak appears at the fourteenth [11] Harris ZL, Migas MC, Hughes AE, Logan JI, Gitlin JD. Familialday. I therefore am in no doubt that Parliament was right to dementia due to a frameshift mutation in the caerulo-plasmin gene.

Quarterly J Med 1996;89:3559.accept the Human Fertilisation and Embryology Act,[12] Tomlinson BE, Blessed G, Roth M. Observations on the brains ofwhich passed both Houses with very large majorities. The

nondemented old people. J Neurol Sci 1968;7:33156.work it is making possible will, I believe, bring inestim-

[13] Tomlinson BE, Blessed G, Roth M. Observations on the brains ofable benefits to human health, not least to the families of demented old people. J Neurol Sci 1970;11:20542.patients with Duchenne dystrophy and to those in which [14] Bowen DM, Smith CB, White P, Davison AN. Neurotransmitter-

related enzymes and indices of hypoxia in senile dementia and otherother serious inherited diseases are present.abiotrophies. Brain 1976;99:45996.

[15] Perry EK, Perry RH, Blessed G, Tomlinson BE. Changes in brain

cholinesterases in senile dementia of Alzheimers type. Neuropathol

8. Conclusions Appl Neurobiol 1978;4:2737.[16] Deary IJ, Whalley LJ. Recent research on the causes of Alzheimers

disease; what causes neuronal death, and why the specific patterns?Mr. Chairman, in expressing yet again my indebtednessBr Med J 1988;297:80710.to you and to all of those concerned in the planning and

[17] Rossor MN. Molecular pathology of Alzheimers disease. J Neurolorganisation of this World Congress, including of course

Neurosurg Psychiatry 1993;56:5836.your very generous sponsors, I thank you for the oppor- [18] Goate A, Chartier-Harlin M-C, Mullan M. Segregation of a missensetunity you have given me of delivering this plenary lecture. mutation in the amyloid precursor protein gene with familial

Alzheimers disease. Nature 1991;349:7046.I hope that in my very selective survey I have been able to[19] Hardy J. The genetics of Alzheimers disease. In: Walton, Lordconvince you that burgeoning developments in neuro-

(Ed.), Alzheimers Disease and the Environment. Royal Society ofscience in this Decade of the Brain, and perhaps above all

Medicine Services, London, 1991, pp. 911.in molecular genetics, have already had a substantial [20] Plassman BL, Breitner JCS. Apolipoprotein E and cognitive declineimpact upon our practice of clinical neurology. Without in Alzheimers disease. Neurology 1996;47:31720.

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