Fanconi anemia is a rare genetic disorder characterized by bone marrow failure and cancer predisposition. It results from defects in DNA interstrand crosslink repair. The disease was first described in 1927 and shows considerable genetic and clinical heterogeneity. Patients have physical abnormalities and bone marrow failure. The main risks are aplastic anemia, leukemia, and solid tumors. Treatment involves blood transfusions, androgens, and hematopoietic stem cell transplant. Management aims to prevent complications and cancers through surveillance and timely intervention.

1. Fanconi anaemia
JG Nel
Department of Haematology and
Cell Biology
UFS
June 2010

2. History
• Most frequently reported IBFS
• First described in 1927 by a
Swiss Paediatrician
• Noted a family with three
brothers who had:
▫ “perniziosiforme anaemia”
▫ Several physical
abnormalities
 Microcephaly
 Skin hyperpigmentation

3. History
• Decades of research into FA
led Fanconi to believe that a
mutation of a single gene
could not account for the
clinical heterogeneity observed
amongst FA patients

4. History
• In 1960s observed by several groups that
cultured cells from patients with FA had an
increased number of chromosomal breaks, the
number of breaks were specifically increased
with the addition of specific agents
• Cell cycle gap in gap2/mitosis also occurred at
lower concentrations of clastogens than in
normal cells

5. In this presentation:
Fanconi anaemia:
• Clinical features
• Molecular and cell biology
• Principles of management
• Morbidity and mortality

6. Clinical features
• Usually inherited as an
autosomal recessive trait
• Can be X-linked recessive
• FA patients display
progressive bone marrow
failure and an increased
predisposition to malignancy

7. Physical findings reported in the
literature
• 60% of reported patients had
at least one feature
• Microsomia 40% of cases

8. Physical findings reported in the
literature
Dermatological 40%
• Café au lait
• Generalized hyper-
pigmentation
• Hypo-pigmented areas

9. Physical findings reported in the
literature
Upper limbs 35%
• Thumbs: (35%)
▫ Absent /hypoplastic, bifid,
duplicated, rudimentary ,
attached by a thread,
triphalangeal, long, low set
• Radii: (7%)
▫ Absent or hypoplastic, absent
or weak pulse
• Hands: (5%)
▫ Flat thenar eminence, absent
first metacarpal, clinodactyly,
polydactyly
• Ulnae: (1%)
▫ Dysplastic, short

10. Physical findings reported in the
literature
Skeletal
• Head: (20%)
▫ Microcephaly, hydrocephaly
• Face: (2%)
▫ Triangular, birdlike,
dysmorphic, micrognathia,
mid face hypoplasia
• Neck: (1%)
▫ Spengel, Klippel-Feil, short,
low hairline, web
• Spine: (2%)
▫ Spina bifida, scoliosis,
hemivertebrae, abnormal
ribs, coccygeal hypoplasia

11. Physical findings reported in the
literature
• Eyes: (20%)
▫ Small, strabismus, epicanthal
folds, hypotelorism, hypertelorism,
cataracts, astignatism
• Renal: (20%)
▫ Horseshoe, ectopic or pelvic,
abnormal, hypoplastic or
dysplastic, absent, hydronephrosis,
hydro ureter
• Gonads:
▫ Males: (25%)
 Hypogenitalia, undescended
testes, hypospadias, micropenis,
absent testes
▫ Females: (1%)
 Hypogenitalia, bicornuate uterus,
malposition, small ovaries

12. Physical findings reported in the
literature
Gastro-intestinal: (5%)
▫ Atresia, imperforate anus,
TOF, annular pancreas,
malrotation
Cardiopulmonary: (6%)
▫ Cong heart dis, PDA, ASD,
VSD, coarctation, situs
inversus, truncus arteriosus
Central nervous system: (3%)
▫ Small pituitary stalk, pitituiary
stalk int synd, absent corpus
callosum, cerebral hypoplasia,
hydrocephalus

13. Clinical features
• Affected individuals may have
one or more somatic
abnormalities
▫ Dermatological
▫ Skeletal
▫ Genitourinary
▫ Gastro intestinal
▫ Cardiac
▫ Neurological
• 1/3 of patients have no overt
somatic abnormalities

14. Clinical features
• Patients with a high congenital abnormality
score(CABS) are at greater risk for developing
aplastic anaemia, whilst patients with lower
CABS are at greater risk of developing solid
tumours or leukaemia as young adults

15. Getting to the heart of the
matter…

16. Fanconi anaemia: Molecular and cell
biology
• Wide range of clinical findings
can be explained by the fact that
FA is a chromosomal instability
disorder
▫ Cells from FA patients
accumulate damage at an
increased rate
▫ Unrepaired DNA damage can:
 Activate pro-apoptotic
pathways –leading to
depletion of haematopoietic
stem cells…
 Can lead to mutations and
translocations that cause
inactivation of cell cycle
barriers leading to
tumour genesis

17. Fanconi anaemia: Molecular and cell
biology
• Abnormal cell cycle kinetics
▫ Prolonged G2 phase
▫ Increased apoptosis
▫ Accelerated telomere
shortening
• Most striking cellular hallmark
of FA
▫ Hypersensitivity to a class of
DNA damaging agents that
create DNA interstrand
crosslinks(ICL)

18. Interstrand crosslinks
• Covalent links that prevent
DNA from unwinding
▫ Blocks transcription and
translation
• Difficult to repair, a single
DNA repair pathway
inadequate
• Affects both strands of the
helix
• Main function of the FA
pathway is to coordinate
several distinct repair
activities

19. Interstrand crosslinks
• Induced by:
▫ Mitomycin C
▫ DEB
▫ ?products of the endogenous
metabolism of certain cells
 ?products of lipid
metanolism in the liver

20. The classic Fanconi Anaemia genes
• Considerable genetic heterogeneity
▫ 13 subtypes/complementation
groups identified
▫ Most inherited in an autosomal
recessive fashion
▫ FANCB -X linked recessive
FANCA
FANCB
FANCC
FANCD1
FANCD2
FANCE
FANCF
FANCG
FANCI
FANCJ/BRIP1
FANCL
FANCM
FANCN/PALB2

21. The core complex
• Majority of FA proteins form a
complex with ubiquitin ligase
activity
• Majority of FA patients
harbour mutations in the
genes that encode the core
complex

22. FANCM and FAAP24: targeting the core
complex to DNA
• Belong to the endonuclease
family
• Normally operate as
heterodimers
• Nuclease domains
▫ Required for dimerization
▫ DNA binding
▫ No nuclease activity
• Recognize stalled replication
forks
• Recruit the core complex to
ubiquinate it’s targets

23. Ubiquination
• Ubiquitin
▫ Smal highly conserved regulatory protein
▫ Ubiquitously expressed
• Ubiquination
▫ Post –translational modification of a protein by the covalent attachment of one or
more ubiquitin monomers
• Functions:
▫ Labeling proteins for proteasomal degradation
▫ Also modulates
 Stability
 Function
 Intracellular localization

24. FANCD2 and FANCI: substrates for
ubiquination
• Dynamic complex that moves
in and out of chromatin
• Monoubiquination considered
an essential step in FAP
activation
• Ubiquination of FANCD2-I
complexes leads to localization
on chromatin foci
• DNA repair structures
▫ Interacts with DNA repair
proteins
 BRCA2,BRCA1,RAD51

25. FANCD2 and FANCI: substrates for
ubiquination
▫ BRCA2
 important in DNA repair by
homologous recombination
 Cells lacking BRCA2-
inaccurately repair damaged
DNA
▫ FANCJ (BRIP1)-”partner of
BRCA1”
▫ FANCN(PALB2)-”partner of
BRCA2”

26. The repair of interstrand crosslinks
• DNA replication blocked at
crosslink
• DSB generated by
endonucleases
▫ Uncouples one sister
chromatid from the other
▫ Crosslinked base can then be
unhooked

27. The repair of interstrand crosslinks
▫ Remaining structure
bypassed by specialized
polymerases that are able to
replicate through DNA
lesions
▫ Bypassed unhooked crosslink
can be repaired by hydrolysis
or nucleotide replacement
allowing re-establishment of
the replication fork
 Likely by HR machinery
mediated invasion of the
repaired chromatid by the
sister

28. ICL repair pathways controlled by FAP
• Nucleotide excision repair
(NER)
• Homologous recombination
(HR)
• Translesion synthesis
(TLR)

29. Nucleotide excision repair
• NER endonucleases perform
the initial incisions that
unhook the crosslink
• Cleavage achieved in a highly
coordinated manner
• Two structure-specific
heterodimeric endonucleases
▫ Erccl-XPF
▫ Mus81-Eme1
• Erccl-XPF cleavage step
required for efficient
recruitment of FANCD2 to the
site of ICL repair

30. Homologous recombination
• Repair initiated by resection of
double strand break
▫ Leaving 3’ single stranded
overhangs
• Central action of HR is
homology search and strand
invasion by ssDNA-Rad51
filament
• Strand invasion into a
homologous sequence is
followed DNA synthesis at the
invading end

31. Homologous recombination
• After strand invasion and
synthesis, the second DSB end
can be captured to form an
intermediate
• After gap repair, DNA
synthesis and ligation the
structure is resolved

32. Translesion synthesis
• DNA damage tolerance
process
• Allows the DNA replication
machinery to replicate past
lesions
• Involves switching out regular
DNA polymerases for
specialized translesion
polymerases

33. Translesion synthesis
• Translesion polymerases
▫ Larger active sites –that can insert
bases opposite damaged
nucleotides
▫ Often have low fidelity (high
propensity to insert wrong bases)
relative to regular polymerases
▫ Many are extremely efficient at
inserting the right bases oppsite
specific types of damage

34. Translesion synthesis
• Risking the introduction of
point mutations during
translesion synthesis may be
preferable to more drastic
mechanisms of DNA repair

35. Fanconi anaemia: The FA/BRCA
pathway
• FA/BCRA pathway activated
by ATR and RAD3 related
protein
▫ ATR directly regulates FA
pathway
 Monoubiquination of
FANCD2
 Phosphorilates FANCD2 at
several sites

36. Management: HSCT
• Only cure for haematological complications is
HSCT
• Timing of HSCT remains a challenge
▫ Outcomes are best prior to the development of
complications
 Infections fromCSN
 High transfusion burden
 Development of MDS/AML
▫ Many patients do not progress to severe marrow
failure or acute leukaemia

37. Management: HSCT
• Patients with FA are VERY sensitive to
genotoxic agents
▫ Cyclophosphamide
▫ Busulphan
▫ Ionizing radiation
• Also sensitive to the damaging effects of graft vs
host disease

38. Management: HSCT
• Reduced doses for transplant preparative regimens
• Nongenotoxic regimens to prevent graft-versus-host
disease
• The use of reduced-intensity conditioning has resulted in
greatly improved transplant outcomes
• Fludarabine
▫ Highly immunosuppressive and myelosuppressive
nucleotide analog
▫ Minimal damage to other organs
▫ Facilitated the reduction of genotoxic agents without
increasing the risk of engraftment failure

39. Management: HSCT
• Matched sibling transplants:
▫ Disease free survival -64-89%
▫ Essential to test all potential sibling donors for FA
 If any abnormality is found sugg. Underlying
marrow dysfunction testing should be conducted on
skin fibroblasts to rule out somatic mosaicism
• Unrelated donor transplants
▫ Discouraging results prior to the advent of
Fludarabine (<30% overall survival)

40. Management: HSCT
• HSCT does NOT correct the non-haematological
manifestations of FA
• Solid tumours:
▫ SCC
▫ risk continues to rise after transplant (4.4 higher
age-specific hazard)
▫ Arise at an earlier age

41. Management: Androgens
• Can improve cytopenias in all three lineages
• Good holding treatment.
• Effect most profound for erythroid lineage
• Subset of patients does not respond at all
• Most patients may respond initially but then
become refractory

42. Management: Androgens
• Dose should be tapered to the minimum that
sustains the blood counts
• May exacerbate liver tumours
▫ Regular monitoring of LFT
▫ Screening US

43. Management: General
• Transfusion support
• Timely institution of appropriate iron chelation
• Treat bleeding
▫ Antifibrinolytics
▫ Platelets
• Annual bone marrow aspirates and cytogenetic
analysis
• Annual surveillance for major solid tumours

44. Morbidity/Mortality
• More than 80% of patients reach an age of 18 years
• Major causes of death in FA
1. Bone marrow failure
2. Leukaemia
3. Solid tumours
• Median survival free of any malignancy or tumours 29 years

45. Morbidity/Mortality
Bone marrow failure
• Usually presents in childhood
▫ Petechiae, bruising, haemorrhages
▫ Pallor, fatigue
▫ infections
• More than 90%develop pancytopenia

46. Morbidity/Mortality
Leukaemia
• 10% of patients
• Most commonly AML
• risk 600 X >general population
Myelodysplastic syndromes
• 6% of patients
• Teens and young adults
• May not have had a phase of aplastic anaemia
• Risk 5000 X >general population

47. Morbidity/Mortality
Solid tumours
• 10% of patients
• Most common:
▫ HNSCC 500X >general population
▫ Liver tumours
▫ Vaginal squamous cell carcinoma 3000X>general population
▫ Brain tumours

48. Take home message
• Classical phenotypes originally
described for IBFS are the
severe end of a highly variable
spectrum
• Early recognition allows
appropriate medical
management and surveilance