Most common microdeletion syndrome is?

ANSWER: (B) VCF syndromeREF: Harrison's 18th ed ch: 62The term contiguous gene syndrome refers to genetic disorders that mimic a combination of single-gene disorders. They result from the deletion of a small number of tightly clustered genes. Because some are too small to be detected cytogenetically, they are termed microdeletions. The application of molecular techniques like FISH has led to the identification of at least 18 of these microdeletion syndromes.Deletions involving the long arm of chromosome 22 (22q11.21) are the most common microdeletions identified to date, present in about 1/3000 newborns. VCF (velo-cardio-facial) syndrome, the most commonly associated syndrome, consists of learning disabilities or mild mental retardation, palatal defects, a hypoplastic aloe nasi and long nose, and congenital heart defects (conotruncal defect). Some individuals with 22q11.21 deletion are more severely affected and present with DiGeorge syndrome that involves abnormalities in the development of the third and fourth branchial arches leading to thymic hypoplasia, parathyroid hypoplasia, and conotruncal heart defects.Some Commonly Identified Ml-Crodeletion and Microduplication Syndromes--FISH AnalysisSyndromeCytogenetic LocationPrincipal FeaturesImprinting EffectsLanger-Giedionsyndrome8q24.1 (del)Sparse hair, bulbous nose,variable mental retardationNoWAGR complex11pl3 (del)Wilms' tumor, aniridia, genitou - rinary disorders, mental retardationNoBeckwith-Wiedemannsyndrome11p 15 (dup)Macrosomia, macroglossia, omphaloceleYes, occasionally associated with 'paternal uniparental disomy"Retinoblastoma13ql4.11(del)Retinoblastoma due to homozygous loss of functional RB alleleNo obvious effect, although abnormal RB allele morelikely to be paternalPrader-Willi syndrome15q11-13(del)Obesity, hypogonadism, mental retardationYes, prototypicimprinting disorderAngelman syndrome15qll-13(del)Ataxic gaitWith Prader-Willi syndrome, prototypic imprinting disorderalpha-Thalassemia and mental retardation16pl3.3(del)Alpha -Thalassemia and mental retr - dation, due to deletion ofdistal 16p, including alpha -globin locusNoSmith-Magenissyndrome17pll.2(del)Brachycephaly, midface hypoplasia, mental retarda-tionNoMiller-Dieker syndrome17pl3 (del)Dysmorphic facies, lissencephalyNoCbarcot-Marie-Tooth syndrome type 1A17pll.2(dup)Progressive neuropathy dueto microduplicationNoDiGeorge syndromevelocardiofacialsyndrome22qll (del)Abnormalities of third and fourth branchial archesNo