Chromosomal Abnormalities

Question 1

Turner Syndrome

Answer 1

Gonadal dysgenesis, short stature, heart defects, fused kidneys, webbed neck, brown nevi, widely spaced nipple, infertility, social difficulty etc.

Meiotic nondisjunction

Question 2

Klinefelter Syndrome

Answer 2

Gonadal dysgenesis/hypogonadism, infertility, tall stature, gynecomastea, high frequency of sterility, language impairment

Meiotic Nondisjunction
Half of cases due to failure of pseudoautosomal recombination (15% are result of mosaicism)

Question 3

XYY Syndrome (Jacobs)

Answer 3

Indistinguishable physically or mentally from normal males and are usually fertile (a little taller); increased risk of behavioral and educational problems, delayed speech and language skills
NOT associated with criminal behavior

Meiotic Nondisjunction
Results from errors in paternal meiosis II, producing YY sperm.

Question 4

Down’s Syndrome

Answer 4

Mid-face hypoplasia, short stature, hypotonia, moderate intellectual disability
Congenital malformations (endocardial cushion defects, duodenal atresia, GI anomalies, Hirschprung disease)	

95% of Trisomy 21 cases are result of non-disjunction in maternal meiosis I
3-4% Robertsonian Translocation (usually extra 21 is fused with chromosome 14, resulting in 45 chromosomes)
1-2% of Mosaic Down’s Syndrome (47,XX+21/46XX)

Question 5

Trisomy 13 (Patau’s Syndrome)

Answer 5

Characteristic facies, severe intellectual disabilities
Congenital malformations (fusion of brain lobes, facial clefts, polydactyly, renal defects)

Question 6

Trisomy 18 (Edward’s Syndrome)

Answer 6

Intrauterine growth retardation, characteristic facies, severe intellectual disabilities, characteristic hand positioning, hypertonicity
Congenital malformations (valvular heart disease, posterior fossa CNS maldevelopment, diaphragmatic hernias, renal defects, seizures)	

Trisomy 18 usually due to translocation der(14, 18)