2Case scenarioA 36-years old woman, G3P2 with one prenatal visit at 35 weeks but otherwise uneventful prenatal course delivers a 3900g female child.At birth the infant is noted to have decreased tone, upslanting palpebral fissures and epicanthal folds.The extremities show single transverse palmar crease
13Numerical chromosomal disorders Euploidy:= 2n = 46 chromosomesAneuploidy:≠ 2nis the state of not having euploidyExamples:Down syndromeTurner syndrome
14Risk factors1- advanced maternal age: Increases the incidence of meiotic errors (non-disjunction). 2- history of unexplained 1st TM abortions. 3- exposure to irradiations. 4- previous baby with chromosomal disorder.
15Aetiology Non-disjunction Abnormal separation of chromosomes during cell division.The result:Extra chromosome = trisomyMissing a chromosome = monosomy
21Trisomy 21 Down syndrome 47,XX+21 47,XY+21 The MC abnormality of chromosomal number.
22Trisomy 21 96% non-disjunction 4% translocation of the long arm of chromosome 21 to chromosome 22
23Trisomy 21 C|P: Hypotonia: improves with age Characteristic facial features:Flattened occiputUpslanting palpebral fissures.Epicanthal folds.Large protruding tongue.Short broad hands.Transverse palmar crease.Wide gap between the first and second toes.
49Turner syndrome The ONLY monosomic viable condition. 45, X0 99% aborted, constituting 13% of all 1st trimester abortions.25% mosaic.Caused by mitotic non-disjunction (post-conceptus mitotic non-disjunction event).So, maternal age is not a risk factor.
69Syndromes involving chromosomal deletions 1. Cri du Chat syndrome2. Williams syndrome3. WAGR syndrome4. Prader-Willi syndrome5. Angelman syndrome
70Prader Willi & Angelman syndromes Both are due to deletion of ch. 15q11Both are caused by “genomic imprenting”.NON-HERITABLE change in DNA.
71Prader Willi & Angelman syndromes If Paternal ch. 15 is missing, either due to:1- Deletion of paternal ch. 152- Uni-parental disomy:Duplication of maternal ch. 15 in absence of the paternal chromosomeThe result is : Prader-Willi syndrome
72Prader Willi & Angelman syndromes If Maternal ch. 15 is missing, either due to:1- Deletion of maternal ch. 152- Uni-parental disomy:Duplication of paternal ch. 15 in absence of the maternal chromosomeThe result is : Angelman syndrome
73Prader-Willi syndrome C|P:MRHypotonia:Improved during the 1st yearAlmond-shaped eyesSmall hands & feetHypogonadotropic hypogonadismobesity
74Angelman syndrome = Happy Puppet syndrome C|P:MRAtaxic movements:Resembling a puppet gaitSeizures:Characterized by inappropriate laughter