Most common chromosomal defect is:
Ans: a (Downs) Ref: Robbins, 7th ed, p. 175Down's syndrome is the most common of the chromosome disorders and a major cause of mental retardation.Cytogenetic abnormalityNon disjunction (MC) = 95%Translocation (robertsonian) = 4 %Mosaicism = 1%Increased maternal age is the main risk factor .Translocation carriers carry high recurrence risk.Clinical features:Cardiac - endocardial cushion defect (MC)HypotoniaGIT - duodenal atresia, TEF, IHPS, Hirschprung disease, annular pancreasMental retardationShort statureMusculoskeletal system - atlantoaxial dislocationMicrocephaly/ brachycephalyRespiratory - recurrent aspiration pneumoniaOpen AFEndocrine - primary gonadal defect, hypothyroidismOblique palpebral fissureHaematopoietic - increased ALL and AMLBmshfield spot. But AML has a betterprognosis than normal individualsDepressed nasal bridgesLow set earsCNS alzhiemers in patients older than 40 yearsShort neck Simian crease,clinodactyly Sandal gap between 1st and 2nd toes Kennedy crease
Down's
Turner
Edward
Patau
Genetics