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Genetic counseling: Fanconi Anemia

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Fanconi Anemia

OverviewEdit

  • Inherited anemia leading to bone marrow failure (aplastic anemia) and myelodysplasia (5%) or acute myelogenous leukemia (10%) and physical abnormalities (60-75%), and increased risk for other cancers

Associated CancersEdit

  • Acute myelogenous leukemia
  • Older patients risk of head and neck, esophageal, gastrointestinal, and genital tract cancers
    • Usually develop after 13 years of age (average age is 23)
    • Difficult to treat due to sensitivity to DNA-damaging agents such a chemo and radiation
  • Patients who receive androgen treatment are at increased risk of liver tumors

Physical Characteristics/symptomsEdit

(25-40% have no physical abnormalities)

  • Short stature (60%)
  • Extreme fatigue
  • Frequent infections
  • Nosebleeds or easy bruising
  • Low white cell, red cell, or platelet count (age of onset highly variable)
  • Myelodysplasia
  • Upper limb malformations: misshapen, missing or extra thumbs or an incompletely developed or missing radius (50%)
  • Other skeletal anomalies (30%) - short low hairline, spina bifida, scoliosis, sacrococcygeal sinus, vertebral anomalies
  • Renal malformations (25%) pelvic, horseshoe, hypoplastic, dysplastic kidney or abnormal artery or abnormal collecting system
  • Abnormal skin pigmentation (café-au-lait spots, hyperpigmentation, hypopigmentation (65%)
  • Microcephaly
  • Eyes (25%) - micropthalmia, strabismus, epicanthal folds, hypertelorism/hypotelorism, ptosis, slanting, cataracts, epiphora, nystagmus
  • Genitalia (40%) -
    • males: hypogenitalia, undescended, absent or atrophic testes, azospermia, delayed puberty. Few males have fathered children
    • females: hypogenitalia, bicornauate uterus, absence of uterus or vagina, ovarian atresia, delayed menarche, irregular menses, early menopause. Successful pregnancies have been reported
  • Ears (10%) - deafness usually conductive due to middle ear anomalies, abnormal pinna, stenosis or atreasia of external auditory meatus, lowest, large or small ears
  • Heart structural defects, cardiomyopathy
  • Lower limbs-toe syndactyly, pes planus, abnormal toes, congenital hip dislocation
  • Mental retardation or learning disabilities
  • Low birth weight
  • Gastrointestinal problems/malformations

Genetic BasisEdit

  • AR inheritance
  • At least 8 FA genes A (16q24.3) 66%, B(?) 4%, C(9q22.3) 12%, D1 rare, D2(3p25.3) rare, E(6p21-22) 12%, F(11p15) rare, G(9p13) rare, (BRCA2 is thought to be B or D1)
  • FA-A and FA-C mutations account for 76% of patients
  • FA pathway regulates DNA repair

IncidenceEdit

  • Found equally in males and females
  • All ethnic groups
  • 1 in 100,000 live births

Carrier frequencyEdit

  • Estimated between 1 in 600 and 1 in 100
  • gene clinics states 1 in 300 for general population in US, Europe and Japan
  • AJ frequency is 1 in 89

Diagnosis and testingEdit

  • Chromosomal breakage studies in presence of diepoxybutane (DEB) or mitomycin C (MMC)
  • Only FA cells exhibit increased chromosomal breakage in response to DEB
  • Chromosomal breakage can be performed prenatally with cells from CVS or amnio
  • If mutations known, mutation analysis can be performed prenatally
  • Chromosome breakage tests don't detect carriers
  • Siblings should be tested since 25-40% of individuals with FA may have no physical abnormalities
  • Complementation studies and mutation analysis available for 6 of the genes on research basis
  • Fanconi Anemia mutation database found at www.rockefeller.edu/fanconi/mutate/
  • FA cell repository in Oregon (will do complementation analysis)
  • Carrier testing available once mutations identified

MosaicismEdit

  • Some cells revert to normal phenotype
  • Attributed to recombination or gene conversion
  • May cause false negative DEB test

Geneotype-PhenotypeEdit

  • Appear to be some correlations

Differential DiagnosisEdit

  • Bloom syndrome, ataxia telangiectasia, and other chromosomal breakage syndromes are all ruled out by DEB chromosomal breakage test
  • NF1 shares café au lait spots
  • Thrombocytopenia with absent radii
  • VACTERL syndrome
  • Above are ruled out by DEB or MMC test

LeukemiaEdit

  • Malignancy where bone marrow produces excess quantities of immature white cells called blasts
  • These suppress the development of healthy blood cells
  • Results in infections and bleeding
  • AML is a particularly aggressive type usually found in older people

Management of FAEdit

(focuses on surveillance of and treatment for physical abnormalities, bone marrow failure, and related cancers)

  • Baseline tests
    • Ultrasound of kidneys and urinary tract
    • Formal hearing test
    • Baseline developmental assessment
    • Referral to ophthalmologist, endocrinologist, and geneticist for initial screening and counseling
    • Follow by hematologist
      • HLA typing of patient, sibs, and parents: full blood typing and blood chemistries
      • Regular blood counts
      • Many recommend annual bone marrow aspirate or biopsy to evaluate morphology, cellularity, and cytogenetics
  • Androgens
    • Improve blood counts in ~50% of patients
    • stimulate production of RBC's, often platelets, sometimes WBC's
    • patients often eventually fail to respond to this treatment
  • Hematopoetic growth factors
    • G-CSF or GM-CSF stimulate production of WBC's in some patients
    • Improved platelet and red cell count in a few patients
    • Generally not recommended for patients with a clonal cytogenetic abnormality
  • Blood transfusions
    • Should be avoided or minimized if patient is a candidate for bone marrow transplantation
    • Family members should be avoided as blood donors to minimize chance of sensitization if considering bone marrow transplant
  • Bone marrow transplant
    • Only long-term cure for blood problems
    • Many associated risks
  • Gene therapy
    • Clinical trials for patients with mutations in A or C gene
    • Potentially correct the hematopoietic defect, but not reduce the risk of developing solid tumors in other tissues
    • Not done if considering bone marrow transplant

ResourcesEdit

  • Fanconi Anemia Cell Repository
Department of Medical and Molecular Genetics
Oregon Health & Science University
3181 SW Sam Jackson Park Rd, L103
Portland, OR 97201
Phone: 503-494-6888
  • Fanconi Anemia Research Fund, Inc (FARF)
1801 Willamette Street, Suite 200
Eugene, OR 97401
Phone: 800-828-4891; 541-687-4658
Fax: 541-687-0548
Email: info@fanconi.org
www.fanconi.org
  • Fanconi Anemia Mutation Registry
www.rockefeller.edu/fanconi/mutate
  • Cancer Fund of America
2901 Breezewood Lane, Knoxville, TN 37921-1009
(423) 938-5281
Supplies and financial aid for low income
cancer patients
  • For more resources see Fanconi Anemia: A Handbook for Families and Their Physicians, 2000

ReferencesEdit

  • Gene Reviews www.geneclinics.com Fanconi anemia
  • Handout from presentation by Dr. Alan D'Andrea
  • Lynn and Dave Frohnmayer. Fanconi Anemia: A Handbook for Families and Their Physicians Third Edition, 2000
  • "Biallelic Inactivation of BRCA2 in Fanconi Anemia" was published in the June 13, 2002 edition of Sciencexpress, one of the on-line versions of the journal Science.
  • Fanconi Anemia Research Fund www.fanconi.org

NotesEdit

The information in this outline was last updated in 2003.



This material has been imported fom the wikibook "Genetic counseling"[ http://en.wikibooks.org/wiki/Genetic_counseling] under the GNU Free Documentation License.

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