MR Syndromes Associated with Chromosomal Abnormalities

Question 1

Down Syndrome

Answer 1

Epi: most common form of inherited MR; Genetic defect: Trisomy 21; Clinical Characteristics: MR, upslanting palpebral fissures, protruding tongue, simian crease, Brushfield spots

Question 2

Fragile X Syndrome

Answer 2

Epi: relatively common form of MR, affects boys more than girls; Genetic Defect: Defect in the X chromosome, mut in 5’ end of gene with CGG repear (200 or more); Clinical characteristics: 20% of boys are normal, 30% of carrier girls are mildly affected, moderate MR, behavioral problems, somatic abnormalities, long face, enlarged ears, macro-orchidism

Question 3

Prader-Willi Syndrome

Answer 3

Epi: uncommon inherited disorder; genetic defect: absence of segment 11 to 13 on the long arm of the paternally derived chromosome 15; clinical characteristics: MR, decreased muscle tone, short stature, emotional lability and insatiable appetite (obesity)

Question 4

Angelman’s Syndrome

Answer 4

epi: uncommon inherited disorder; genetic defect: deletion of segment 11 to 13 on the maternally derived chromosome 15; clinical characteristics: MR, abnormal gait, speech impairment, seizures, inappropriate happy behavior that includes laughing, smiling and excitability (happy puppet syndrome)

Question 5

Rett’s Syndrome

Answer 5

epi: progressive neurodevelopmental disorder, generally girls only, 1 in 100,000 births; genetic defect: MeCP2 on long arm of chromosome X; clinical characteristics: normal development until 6 to 18 months, a first sign is hypotonia, autistic-like behavior, stereotyped hand movements (wringing and waving), lag in brain and head growth, gait abnormalities, seizures