10: Chromosomal Disorders And Other

Question 1

Mosaics in Down Syndrome

Answer 1

Mixture of cells with either 46 or 47 chromosomes -> milder sx

Question 2

Four reasons Down Syndrome research has been slow

Answer 2

1. Results from gene dosage imbalance
2. Majority of protein genes are overexpressed (ex: APP)
3. About 10% of overexpressed genes are involved in mitochondrial regulation
4. Chr 21 has highest density of lncRNAs

Question 3

A non-invasive screening test for prenatal dx of Down Syndrome

Answer 3

5-10% of total cell free DNA in maternal blood is from fetus

Question 4

DiGeorge Syndrome triad

Answer 4

Thymic hypoplasia with T cell immunodeficiency + parathyroid hypoplasia with hypocalcemia + cardiac malformations

Question 5

Velocardiofacial syndrome

Answer 5

Facial dysmorphism (prominent nose, retrognathia), cleft palate, CV anomalies, learning disability

Question 6

What occurs with 2+ X chr and 1+ Y chr?

Answer 6

Male hypogonadism

Question 7

Risks involved with Klinefelter syndrome

Answer 7

1. DM II and metabolic syndrome
2. Mitral valve prolapse, ASD, VSD
3. Osteoporosis, fractures
4. Extragonadal teratomas
5. Breast cancer
6. Autoimmune (esp SLE)

Question 8

Common occurence for fetus with Turner Syndrome

Answer 8

Cystic hygroma: general swelling + in nape of neck due to lymph stasis

Question 9

Single most important cause of primary amenorrhea

Answer 9

Turner syndrome

Question 10

Streak ovaries

Answer 10

Ovaries become atrophic and fibrous, devoid of ova and follicles

Question 11

First and second most common genetic cause of intellectual disability

Answer 11

1. Down Syndrome

2. Fragile X Syndrome

Question 12

Carrier males vs females in fragile X syndrome

Answer 12

Males: 20% of carriers are totally normal “normal transmitting males”
Females: 30-50% are affected, much higher than in other X-linked recessive disorders