Sue Griffin, PhDDillard Professor and Vice ChairDonald W. ReynoldsDepartment of GeriatricsUniversity of ArkansasFor Medical SciencesResearch DirectorGRECC VAMCLittle Rock, Arkansas

The GeneticsOf Alzheimer’s

Genes are onchromosomespresent in thenucleus ofevery cell

The genetic code has four letters:A=adenine, T=thymine, G=guanine, C=cytosine

Chromosomesin the nucleus

The yellow ribbon is held together by A—T

and C—G

ChromosomalDNA (genes)carry the codefor all proteinsnecessary tomake our body

Facts:

• A complementary strand (messenger RNA) is made to nuclear DNA—an A on the mRNA is paired with a T on the gene and C with G, over and over to code for the building blocks (amino acids) needed to make every protein!

• Every amino acid has a unique code

Diversity of Genetic DiseasesSimplistic:

• One gene mutation causes every case.

More Complex:• Multiple gene mutations cause all cases.

Most Complex:• Multiple gene mutations cause some cases.• Multiple polymorphisms increase risk.• Multiple environmental factors increase risk.

What Starts EverythingGoing Wrong

In Alzheimer’s Disease?

• The genes you inherit (nature)• Wear and tear of time (aging)• The way you handle your inheritance (nurture)

When You’reOld but Okay

Nerve Cells andHow They WorkIn Normal Brain

• The nucleus• The cytoplasm• The processes• The transmission of information

When your brain is hot and fine

                                                                                                                                                                                                                                        

Progression from Hearing to Speaking and from Reading to

Mulling It All Over

MILD MODERATE SEVERE

Affected Regions at DifferentStages of Alzheimer’s Disease

Clincally Normal Alzheimer’s disease

When the Brain “Cools Down”

The Problem in Alzheimer’sDisease fromOne of His Own Cases

MB Graeber 1997 Neurogenetics

Aβ plaques, activated glia, neuronal DNA10 µm

• The -pleated sheet protein -amyloid (A)

• This is important!!

• George Glenner sequenced the protein and Konrad Beyreuther, Dmitry Goldgaber, and St. George-Hyslop and colleagues mapped the Aprecursor protein (APP) gene to chromosome 21

What is that sticky insoluble stuff in plaques?

APP is Cleaved to Form -amyloid

Functions of APP

• Responds to injury• Membrane Functions• Interacts with PS1

Reasoning Behind This Discovery?

• People with Trisomy 21 have Alzheimer A plaque pathology by middle age (Wisniewski, 1989)

• Plaques in Down’s as in Alzheimer’s are the product of APP cleavage, so it’s logical that mutations in APP cause the disease in families with lots of Alzheimer’s. Tanzi and others took this candidate gene approach (Plan A in genetic studies).

Hypothesis:

Fact:

Plan A - Sequence a Specific Gene

Studies of Alzheimer families that were based on a pathological characteristic of the disease

• Because A plaques were the most prominent neuropathological feature, APP was the targeted gene in AD in these families.

• At least three offending APP mutations in DNA from family members have been identified by searching for mutations by mapping of this gene.

APP Mutations Cause Alzheimer’s

Disease . . How did we come to know this??

We thought that we were nearly there! The cause! Yes!

But that was only 1989 and . . .

• Then they asked: Do all family members with the mutation have the disease? Yes• Do family members who don’t have the mutation have the disease? No (Maybe?)

If yes on the first and no on the second = Disease associated, Causative, and Dominant!

Family Association Studies

Hmm ~ Why MaybeNot all familial Alzheimer’s disease families have mutations in this gene

And all of the known APP mutations taken together don’t account for all of

the people (>5%) with familial Alzheimer’s

So Plan B - Mapping Studies -Identified Two Other Causative Genes • Taking a more unbiased approach—that is, not looking for a missense sequence in a specific protein—researchers used endonucleases to cleave DNA for restriction fragment length polymorphism (RFLP) studies to identify aberrant cleavage sites. This type of chromosome mapping, identified two more mutated genes (Presenilin-1 and -2) that, like APP mutations, are causative for Alzheimer’s disease.

• Restriction endonucleases are enzymes that cleave DNA at specific sites.

• Absence of a cleavage site can be used to identify a missense or mutated site

Notes on RFLP Studies

• RFLP mapping of DNA from a case control study identified a chromosome 19 region that associated with, but not causative of, Alzheimer’s disease. The variant was ApoE 4.

Plan B Also Identified one of three Apolipoprotein E polymorphisms (4)

Associated with Increased Alzheimer Risk

Mutations:Several in the APP GenePresenilin 1 and 2 Genes

Copy Number:

Polymorphisms:APP e.g. Down’s syndrome

Apolipoprotein E GenesInflammatory Genes

ApoE Facts

• The ApoE ε4 gene carries a high relative risk:

• There are three variants—2, 3, and 4.

• Inheritance of 4 increases Alzheimer risk 3-9X.

• More than half of Alzheimer patients have one or more 4 alleles.• Inheritance of the 2 allele may be protective.

• ApoE is important in transport of lipoproteins. But its specific role in neurons is unknown.

These isoforms differ from each other only by single amino acid substitutions at positions 112 and 158 of the 299 amino acid protein but have profound physiological consequences. E2 is uncommon but is associated with both increased and decreased risk for atherosclerosis. Approximately 64 percent of the population carries one or two E3 genes. E3 is the "neutral" Apo E genotype. E4 has been implicated in athero-sclerosis and Alzheimer's disease, impaired cognitive function, and reduced neurite outgrowth. ApoE is a target gene of liver X receptor, a nuclear receptor member that plays a role in metabolic regulation of cholesterol, fatty acid, and glucose homeostasis. Look in Wikipedia

Some ApoE 2, 3, and 4 Facts

APP is Cleaved to Form -amyloid

Functions of APP:

• Expression increasesin response to injuryand in aging• Membrane Functions• Interacts with PS1

ApoE Regulates APP Expression

NeuronsIn Culture

ApoE3 ApoE4

AlzheimerBrain

Plaque proximity = less neuronal APP

A APP Nuclei

One Important Driver

A neuroinflammatory Cytokine named interleukin-1 (IL-1).

Why would I say that?What can IL-1 drive?

What Does IL-1 Do?• To Neurons Increases production of: i) APP ii) Faulty tau (hyperphosphorylated) iii) Enzymes that breakdown neurotransmitters Decreases production of: i) synaptophysin

Neuro-fibrillary Tangles

(red)IL-1 in

Microglia(green)

Interleukin-1 has aSister Cytokine ~ TNF

1.TNF and IL-1 are both elevatedin Alzheimer’s disease.2. They induce each other and actas neuroinflammagens.3. Both act as gliotransmitters.

YesAre their heritable variants of the genes that encode these drivers that might increase risk for Alzheimer’s disease?

Probably

IL-1 Genotype and Age at Alzheimer’s Onset

Factor Odds Ratio ApoE 4 5.5IL-1A 2,2 4.9

Grimaldi, Griffin, et al. Ann Neurol, 2000

Confirmation of an Old Idea1. Breitner JC et al Neurology 1994;44:227 2. in ’t Veld BA et al Neurobiol Aging 1998;19:607 3. Zandi PP et al Neurology 2000;54:20664. Vlad SC et al Neurology 2008;70:16725. Szekely, C. A. Neurology 2008;70:17

Adjusted odds ratios of Alzheimer’s for ibuprofen ( ) and naproxen ( )

Combat Strategies

•Prevention: Exercise Diet and Stop Smoking

Combat Inflammation

•Treatment: Education and Cognitive Reserve Meds: Aricept, Namenda

We are our genes

But we get to decide what we do about our genetics!