<prompt> Which of the following chromosomes is involved in Patau syndrome?Chromosome 13Chromosome 18Chromosome 21Chromosome 5  <response>: Ans. a Chromosome 13 Ref. Robbins 7th176; H-17th410Paragraph from Robbins Pathology 7th ed. p. 176under the subheading Other trisomies Trisomies involving chromosome 8, 9, 13, 18, and 22 have been described.- Trisomy 13 is Patau syndrome- Trisomy 18 is Edward syndrome- Trisomy 21 is Down syndromeTRISOMEES By far the most common chromosomal abnormality is trisomy, which is identified in -25 of spontaneous abortions and 0.3 of newborns. Trisomy 16 is extraordinarily common, accounting for about one-third of all trisomies in spontaneous abortions. There is strong association between increasing maternal age and trisomy.- Under the age of 25, -2 of pregnancies are trisomic;- By the age of 36, -10 of pregnancies are trisomic; and- By the age of 42, 33 of pregnancies are trisomic. The risk of Down syndrome as per maternal age:0 OP Ghai 7th!613- 1:1550 if age 15-29 yrs- 1:800 at 30-34 yrs- 1:270 at 35-39 yrs- 1: 100 at 40-44 yrs- 1: 50 after 45 yrs.Autosomal trisomies:TrisomyFeaturesClues to rememberDown syndrometrisomy 21, 1:700Findings: intellctual disability, flat facies, prominent epicanthal folds, single palmar crease, gap between 1st 2 toes, duodenal atresia, Hirschsprung disease, congential heart disease most commonly ostium primum-type atrial septal defect , Brushfield spots. Associated with - risk of ALL, AML, and Alzheimer disease 35 years old.95 of cases due to meiotic nondisjunction of homologous chromosomes associated with advanced maternal age; from 1:1500 in women 20 to 1.25 in women 45 years old.4 of case due to Robertsonian translocation1 of cases due to mosaicism no maternal association; post-fertilization mitotic error.Drinking age 21.Most common viable chromosomal disorder and most common cause of genetic intellectual disability.First-trimester ultrasound commonly shows; nuchal translucency and hypoplastic nasal bone; serumPAPP-A is , free b-hCG is .Second-trimester quad screen shows; a-fetoprotein, b-hCG, estriol, inhibin A.Edwards syndrome trisomy 18, 1:8000Findings: severe intellectual disability, rocker-bottom feet, micrognathia small jaw, low-set Ears, clenched hands, prominent occiput, congenital heart disease, Death usually occurs within 1 year of birth.Election age 18.Most common trisomy resulting in live birth after Down syndrome.PAPP-A and free b-hCG are in first trimester. Quad screenshows: a-fetoprotein, b-hCG, estriol, or normal inhibin A.Patau syndrome trisomy 13, 1:15000Findings: severe intellectual disability, rocker-bottom feet, microphthalmia, microcephaly, cleft lipPalate, holoProsencephaly, Polydactyly, congenital heart disease. Death usually occurs within 1 year of birth.Puberty 13.First-trimester pregnancy screen showns: free b-hCG, PAPP-A, and nuchal translucency. 