<prompt> Most common microdeletion syndrome is?WAGR syndromeVCF syndromePrader villi syndromeAngelmann syndrome  <response>: ANSWER: B VCF syndromeREF: Harrisons 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 13000 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 delSparse hair, bulbous nose,variable mental retardationNoWAGR complex11pl3 delWilms tumor, aniridia, genitou - rinary disorders, mental retardationNoBeckwith-Wiedemannsyndrome11p 15 dupMacrosomia, macroglossia, omphaloceleYes, occasionally associated with paternal uniparental disomyRetinoblastoma13ql4.11delRetinoblastoma due to homozygous loss of functional RB alleleNo obvious effect, although abnormal RB allele morelikely to be paternalPrader-Willi syndrome15q11-13delObesity, hypogonadism, mental retardationYes, prototypicimprinting disorderAngelman syndrome15qll-13delAtaxic gaitWith Prader-Willi syndrome, prototypic imprinting disorderalpha-Thalassemia and mental retardation16pl3.3delAlpha -Thalassemia and mental retr - dation, due to deletion ofdistal 16p, including alpha -globin locusNoSmith-Magenissyndrome17pll.2delBrachycephaly, midface hypoplasia, mental retarda-tionNoMiller-Dieker syndrome17pl3 delDysmorphic facies, lissencephalyNoCbarcot-Marie-Tooth syndrome type 1A17pll.2dupProgressive neuropathy dueto microduplicationNoDiGeorge syndromevelocardiofacialsyndrome22qll delAbnormalities of third and fourth branchial archesNo 