<prompt> Downs syndrome is associated with mental retardation. Which of the following abnormalities are not found in Downs syndrome?Deletion 21Trisomy 21Translocation t 13,21, t 21,21Mosaic 21  <response>: Ans. a. Deletion 21 Ref: Robbins 9 epi61. 8c pi611Deletion of chromosome number 21 is not seen in Downs syndrome.Approximately 95 of Downs syndromes have trisomy 21, so their chromosome count is 47. Studies in which DMA polymorphisms were used to trace the parental origin of chromosome 21. the extra chromosome is of maternal origin. In about 4 of cases of Down syndrome, the extra chromosomal material derives from the presence of a robertsonian translocation of the long arm of chromosome 21 to another acrocentric chromosome e.g., 22 or 14. Approximately 1 of Down syndrome patients are mosaics, usually having a mixture of cells with 46 and 47 chromosomes. Down s Syndrome Trisomy 21 It is the 1C of the chromosomal disorders and a major cause of mental retardation Mitotic non-disjunction is responsible for development of mosaicism. Genetics of Down syndrome Meiotic NondisjunctionRobertsonian translocationMosaicism Seen in 95 cases with trisomy 21. MC cause of Down syndrome Extra chromosome is of maternal origin. Strong relation with maternal age Seen in about 4 of cases of Down syndrome. Extra chromosomal material derives from the presence of a robertsonian translocation of the long arm of chromosome 21 to another acrocentric chromosome e.g., 22 or 14. Most cases are but not always familial. No relation with maternal age Seen in -1 of Down syndrome patients Results from mitotic nondisjunction of chromosome 21 during an earfy stage of embryogenesis. Patients have a mixture of cells with 46 and 47 chromosomes mosaicism. No relation with maternal age. Features of Down Syndrome My Child has Problem Mental retardationMicrognathia Congenital heart diseaseCataracts.Clinodactyly HypotoniaHypothyroidism Increased gap between 1st and 2nd toe Sandle toe Leukemia riskLung problem Increased risk of respiratory tract infections Duodenal atresia Hirschsprungs diseaseHearing loss Alzheimers diseaseAtlantoaxial instability Simian crease Single palmar fold Protruding tongue Round faceRoliing eye nystagmus Occi put flatOblique pa Ipebrai fissure mongoloid slant Brushfteld spotBrachycephaly Low nasal bridge,Language problem E pica nthic foldEar foldedMongolian slantMyoclonusComplications of Downs syndrome Congenital cardiac defects NIC is VSD Increased risk of leukemia particularly ALL more commonly and specifically the megakaryoblastic form of AML M7-AML Hypothyroidism Reduced fertility in females Males are totally infertilejl Increased risk of respiratory tract infections First and second trimester Down syndrome screensScreenPerformed atDetection rateFalse positiveDescriptionTriple test15-20 weeks705Maternal serum AFP Low Estriol Low hCG HighQuad screen15-20 weeks815Triple test Inhibin-alpha HighFirst trimester combined test10-13 weeks855Ultrasound to measure:Nuchal translucency IncreasedDuctus venosus flow reversedNasal bone hypoplasia hCG Pregnancy associated plasma protein A, PAPPA LowIntegrated test10-13 weeks and15-20 weeks955Measurements from both,the 1st trimester combined test and 2nd trimester Quad test to yield a more accurate screening result 