SPEAKER PRESENTATION Open Access

Chromosomal instability and molecular mutationsin multi spectrum disease of Fanconi anemiaBabu Rao Vundinti

From International Conference on Human Genetics and 39th Annual Meeting of the Indian Society ofHuman Genetics (ISHG)Ahmadabad, India. 23-25 January 2013

Fanconi anemia (FA; MIM no. 227650), the most com-monly inherited bone marrow disorder, has an overallprevalence of 1–5 per million and an estimated carrierfrequency of 1:200-300 in most populations. Demon-strating either an autosomal or X-linked recessive modeof inheritance, FA is characterized by childhood pro-gressive bone marrow failure and predisposition toacute myelogenous leukemia, older patients are atincreased risk for squamous cell carcinomas of the head,neck, and genitourinary tract. Congenital abnormalitiesare present in approximately 70% of FA patients andmay include radial ray defects, cafe´ au lait spots orhypopigmentation, short stature, microphthalmia, mal-formations of kidneys, gastrointestinal tract, and heart,mental retardation, and hearing defects. Because of thehigh degree of phenotypic variability exhibited by FApatients, diagnosis may be difficult on the basis of clini-cal manifestations alone. Because FA patient-derivedlymphocytes and fibroblasts exhibit hypersensitivity toDNA crosslinking agents such as diepoxybutane (DEB)and mitomycin C (MMC), resulting in a high rate ofchromosomal breakage and radial formation, analysis onthe basis of this hypersensitivity has been routinely usedto confirm clinical diagnosis.Molecular diagnosis of FA has been challenging

because of the genetic heterogeneity associated with thedisease. To date, 15 FA gene products (FANCA, B, C,D1, D2, E, F, G, I, J, L, M, N, O and P) have been iden-tified and they constitute the FANC pathway, which isthought to function in preventing genome instability.The FA core complex comprises FAAP24, FAAP100,and 8 FA proteins (FANCA, B, C, E, F, G, L, and M)and mediates DNA-damage-induced or replication-stressinduced monoubiquitylation of FANCD2 and FANCI.

Monoubiquitinated FANCD2 and FANCI translocate tochromatin and function in DNA repair at least partiallyby recruitment of FAN1 nuclease. Cloning of the FANCgenes has provided a means, via complementation groupanalysis, to routinely pinpoint the patient’s specific FAgene harboring the mutations, thus greatly simplifyingsubsequent molecular analysis. Although retroviral-mediated complementation analysis of FA patient-derived cells is commonly used to identify the patient’sgenetic subtype as a prerequisite for mutation screening,such analysis has not been formally validated for clinicaluse. Previous studies have considered Fanconi comple-mentation Group A (FA-A) assignments, but none haveperformed comprehensive sequencing to verify comple-mentation assignment and/or evaluated complementa-tion assignments performed using retroviral-mediatedrescue as evidenced by correction of MMC and DEB-induced chromosome breakage and radial formation.Among all complementation groups, FAA accounts forthe majority of FA patients (60–65%) followed by FAC(10%) and FAG (9%). Mutations in the gene for comple-mentation group FA-A (FANCA; MIM no. 607139) con-fer autosomal recessive inheritance and account forapproximately 66% of all FA cases. The FANCA gene ismapped to chromosome 16q24.3,11 spans approximately80 kb of genomic DNA (gDNA), and consists of 43exons. With more than 200 different mutationsdescribed thus far, the FANCA mutation spectrum isvery heterogeneous. Because of the presence of a largenumber of Alu repeat sequences within the FANCAgene, large intragenic deletions involving multiple exonshave been reported to account for more than 40% of allFANCA mutations.First time we have carried out a molecular study in

the Indian population. We have studied FA by chromo-somal breakage study using mitomycin C (MMC) andCorrespondence: vbaburao@hotmail.com

ICMR- National Institute of Immunohaematology, Parel, Mumbai, India

Vundinti Molecular Cytogenetics 2014, 7(Suppl 1):I47http://www.molecularcytogenetics.org/content/7/S1/I47

© 2014 Vundinti; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction inany medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

diepoxybutane (DEB) induction and FANCD2 monoubi-quitination by western blotting to understand genedefects in FA pathway. The complementation analysiswas done by retroviral transfection. The molecular studywas carried out by Multiplex Ligation-dependent ProbeAmplification (MLPA) and direct sequencing ofFANCA, C, G, E, F, L, and M genes. The complementa-tion analysis results showed different spectrum as com-pared to world literature. Our study revealed FA-A andE gene defects in 69% cases and followed by FANCEgene defect. The molecular analysis showed the largedeletions in 11 patients and FANCA gene mutationswere in 12 FA patients. Out of 12 mutations 5 mutations(c.3678 C>G, p.Ser 1226 X, c.3993G>A p.Leu 1331 Pro,c.1274 C>G p.Glu 425 His, c.2630 C>G p.Ser 877 X)found to be novel mutations. In our series the singlenucleotide polymorphisms (SNP); Exon9,c.796A>G(p.Thr266Ala), Exon16,c.1501G>A(p.Gly501Ser), Exon26,c.2426G>A(p.Gly809Asp), of FANCA gene also observedin 23 patients, and these polymorphisms in disease asso-ciation was reported in FA database, however, it needs tobe established in Indian population. Interesting finding ofour study is the existence of FANCE mutation in Indianpopulation, and the same was reported rarely in otherplaces of the world. The study also highlighted theuncharacterized FA patients, which may associated withnew genes in Indian population and these patients shouldbe studied molecularly and genotype-phenotype correla-tion need to be established, which helps in better under-standing and management of the disease.

Published: 21 January 2014

doi:10.1186/1755-8166-7-S1-I47Cite this article as: Vundinti: Chromosomal instability and molecularmutations in multi spectrum disease of Fanconi anemia. MolecularCytogenetics 2014 7(Suppl 1):I47.

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Vundinti Molecular Cytogenetics 2014, 7(Suppl 1):I47http://www.molecularcytogenetics.org/content/7/S1/I47

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