RARE DISORDERS OF IRON METABOLISM

Clara CamaschellaVita-Salute University and San Raffaele Scientific Institute

Milano, Italy

Madrid, 3rd European Symposium on rare anemiasNovember 19, 2010

Body iron distribution

(Andrews, NEJM, 1999)

Liver expressed antimicrobial 25 amino acid peptide

Key regulator of iron homeostasis

Hepcidin: the key iron regulator

hepcidin

Fe

Liver

macrophagesenterocytes

Fe

Fe

Systemic iron regulation

(Hentze et al, Cell 2010)

Disorders of hepcidin deficiency

Genetic disordersHereditary hemochromatosis type 1,2,3

(Hemochromatosis type 4 may be due to ferroportin mutations that are hepcidin-resistant)

Acquired disorderssecondary iron overload in iron loading anemias

Hemochromatosis:molecular genetics

Type 1, AR: classic type HFE mutations

Type 2, AR: juvenile hemochromatosis: hepcidin (HAMP) or hemojuvelin (HJV)

mutations

Type 3, AR: TFR2 mutations

Type 4, AD: “ferroportin disease” FPN mutations

HFE

HJV

HAMP

TFR2

FPN

6

1

19

2

7

Hemochromatosis: pathogenesis

The genetic defect causes inappropriately high intestinal iron absorption and macrophage iron recycling leading to:

increased transferrin saturation increased serum ferritin iron accumulation in parenchymal organs iron toxicity and organ failure

skinskin

jointsjointspancreaspancreas

heartheartDietary ironDietary iron

pituitary

liverliver

Hemochromatosis: Clinical complications

The most common form: HFE-relatedLate onset (middle age) - Low penetrance, prevalent male expressionHigh TS, high SF, iron in hepatocytes

Liver fibrosis, cirrhosis, HCC

Heart failure, arrhytmias,

Glucose intolerance, diabetes

Hypogonadism; other endocrinopathies

Arthropathy - Skin pigmentation

HFE hemochromatosis: genotypes at risk

C282 homozygous (60-95%)

C282Y/H63D compound (5-10%)

H63D homozygous (rare)

Other HFE mutations

C282Y or H63D heterozygous: search for additional factors

Murine models: Hfe -/-, HfeC294Y/C294Y, liver conditional k.o.

Autosomal recessive – rare

Early onset (II-III decades)

Both sexes affected

Severe iron overload

Progressive disease

Mutations of hepcidin

or hemojuvelin

Juvenile (Type 2) hemochromatosis

liver

heart

pituitary

10203040506070

HFE JH

anni

Hjv -/- and Hamp -/-

TFR2- (Type 3) hemochromatosis

Autosomal recessive, rare

High transferrin saturation, Iron in hepatocytes

Clinical complications as in HFE-disorder

Early onset but not severe

Responsive to phlebotomy

(Camaschella et al, Nat Genet 2000)

Tfr2 Y245X/ Y245X

Wild type

Fleming et al, PNAS 2002

(Ganz et al. Blood 2008;112:4292-4297)

Hepcidin dosage by ELISA in hemochromatosis

Hepcidin regulation by iron

Type 4 Hemochromatosis

Heterogeneous condition due to heterozygous mutations of the iroexporter ferroportin - Autosomal dominant

Type ANormal transferrin saturation, high serum ferritinMacrophage iron loadingMild anemia or phlebotomy intoleranceMutant ferroportin protein do not reach the plasma membrane

Type B High transferrin saturation, high serum ferritin Hepatocyte iron loading. Mutant ferroportin protein are hepcidin-resistant (e.g. C326S)

Disorders of hepcidin deficiency

Genetic disordersHereditary hemochromatosis type 1,2,3

(Hemochromatosis type 4 may be due to ferroportin mutations that are hepcidin-resistant)

Acquired disorderssecondary iron overload in iron loading anemias

Defective hepcidin activation: iron loading anemias (thalassaemia)

Tf sat % 33 79 95

Ferritin ng/ml 178 627 2,748

Hb g/dL 14.6 8.8 11.3

sTfR 1.4 47 12

(Orita el al Haematologica 2007 and Nemeth, personal comunication)

Hep

cidi

n (n

g/m

g cr

eat)

normal TI TM

10

100

1,000

Hepcidin inhibition in erythropoiesis expansion

Disorders of Hepcidin excess

Acquired disordersAnemia of chronic diseases (ACD)

Genetic disordersIron refractory iron deficiency anemia (IRIDA)

Inappropriate high hepcidin: IRIDA

IRIDA = iron refractory iron deficiency anemiaAutosomal recessive disorder due to TMPRSS6(matriptase 2) mutations Moderate anemia, severe microcytosis

(Finberg et al, Nat Genet 2008, Sem Hematol 2009)

Extremely low iron and transferrin saturationNormal serum ferritinHigh serum (and urinary) hepcidin levelsRefractory to oral and partially refractory to iv iron

Matriptase-2

CN TM CUB LCUB LL SERINE PROTEASESEA

MT-2 is encoded by TMPRSS6 gene on chromosome 22

RNA expression: liver (kidney, olfactory epithelium)

Protein: 811 amino acid type II transmembrane serine protease synthesized as an inactive zymogen

(TTPS family: enteropeptidase, hepsin,corin, matriptase 1…)

Cleavage activity indispensable for function.

Y141

CL1

66fs

I212

T

Q22

9fs

W24

7fs

R27

1Q

C51

0S

S561

XS5

70fs

E486

D

S304

L

A118

D

Y335

XY3

93X

G44

2RE4

61fs

D52

1NE5

22K

Mas

kR

599X

A605

fsK

636f

s

P686

fs

R77

4C

Mutations associated with IRIDA

L674

F

(Silvestri et al Blood 2009De Falco et al, Hum Mut 2010)

↓HEPC

SMADs

BMP

BMPR

m-HJV

TMPRSS6

↑ serum iron

normalerythropoiesis

↑HEPC

SMADs

BMP

BMPR

m-HJV

TMPRSS6

↓ serum iron

IRIDA

Model of hepcidin regulation by matriptase-2

(Silvestri et al Cell Met 2008)

Mean±SDHb g/dl (at presentation)

7.7±1.3

Hb g/dl (at diagnosis)

9.21±1.8

MCV fl 55.47±7.6Transferrin saturation %

5.03±2.3

Ferritin ng/ml 126±82Serum hepcidin nM 257±157*Urin. hepcidin ng/mg creat

4113±3089*

IRIDA: hematological data (32 published cases)

IL-1liverIL-6

hepcidin

Hepcidin in inflammation

LPS

Reduced iron absorptionReduced iron recyclingIron retention in macrophagesIron restricted erythropoiesis(ACD)

(Ganz, T. et al. Blood 2008;112:4292-4297)

Hepcidin dosage by ELISA in inflammation

Recent reports of increased hepcidin in patients series of Hodgkin diseases, RA, Multiple Myeloma….

Disorder Gene OMIM n

Defects of iron transport/uptake Hypotransferrinemia TF #209300DMT1 mutations DMT1 #206100

Defect of iron absorption IRIDA TMPRSS6 #206200 Defects of iron recycling

Aceruloplasminemia \ CP #604290Defects of cellular iron utilization

Sideroblastic anemiaX-linked sid. anemia ALAS2 +301300AR sideroblastic anemia SLC25A38 #205950

GLRX5X-linked sid. anemia/ataxia ABCB7 #30131

Inherited microcytic anemias

Atransferrinemia DMT1 mutations

Tmprss6 mutations

Hb low low low

MCV low low low

Fe low high low

Tf Low/absent low high

Tf sat high high low

ferritin high high normal/high

hepcidin low low high

Differential diagnosis of iron-related inherited anemias

How to suspect genetic iron-related anemias

Family history

Microcytic anemia since childhood (or birth)

Atypical iron parameters

Serum ferritin not consistent with transferrin saturation

Lack of response to oral iron, hihg hepcidin levels(IRIDA)

E-RARE project on microcytic anemias (ERARE-115, HMA-IRON)

•Dr. Carole Beaumont (France)

•Dr. Clara Camaschella (Italy)

•Dr. Martina Muckenthaler (Germany)

•Dr. Mayka Sanchez (Spain)

Acknowledgments

CEINGE & University of NaplesAchille IolasconGina De Falco

University of BresciaPaolo Arosio

University of VeronaDomenico Girelli

Laura SilvestriAlessia PaganiAntonella Nai

Vita-Salute University and San Raffaele Scientific Institute

E-rare Call 2009