Genetics IV

Question 1

Name the four most common trinucleotide repeat disorders and list their repeat sequences.

Answer 1

1.) Fragile X Syndrome (CGG); 2.) Friedreich’s ataxia (GAA); 3.) Huntington’s Disease (CAG); 4.) Myotonic dystrophy (CTG) (p.87)

Question 2

Describe the most common clinical findings in Down’s Syndrome.

Answer 2

Mental retardation, flat facies, prominent epicanthal folds, simian crease, gap between 1st and 2nd toes, duodenal atresia, congenital heart disease (most commonly ostium primum type ASD (p.88)

Question 3

Name two comorbitities of increased prevalance in Down’s Syndrome patients.

Answer 3

ALL and Alzheimer’s Disease (p.88)

Question 4

What are the results of a pregnancy quad screen and an ultrasound in a fetus with Trisomy 21?

Answer 4

Pregnancy Quad Screen: decreased alpha-fetoprotein; increased b-hCG; decreased estriol; increased inhibin A. Ultrasound shows increased nuchal in first trimester translucency (p.88)

Question 5

What is Edward’s Syndrome?

Answer 5

Trisomy 18, most common trisomy following Downs. Findings include severe mental retardation, rockerbottom feet, micrognathia (small jaw), low set ears, clenched hands, prominent occiput, congenital heart disease and death usually within one year (p.88)

Question 6

What are the results of the pregnancy quad screen in a fetus with trisomy 18?

Answer 6

Decreased alpha fetoprotein, decreased b-hCG, decreased estriol, normal inhibin A (p.88)

Question 7

What is Patau’s syndrome?

Answer 7

Trisomy 13. Findings include severe mental retardation, rockerbottom feet, micropthalmia, microcephaly, cleft lip/palate, holoprosencephaly, polydactyly, congenital heart disease, death usually within one year (p.88)

Question 8

What are the results of the pregnancy quad screen in a fetus with trisomy 13?

Answer 8

Decreased PAPP-A, decreased b-hCG, increased nuchal translucency (p.88)

Question 9

What is a robertsonian translocation?

Answer 9

Nonrecriprocal chromosomal translocation that commonly involves chromosome pairs 13,14,15, 21, and 22. It occurs when the long arms of 2 acrocentric chromosomes (chromosomes with centromeres near their ends) fuse at the centromere and the 2 short arms are lost (p.88)

Question 10

What is the difference between a balanced and unbalanced robertsonian translocation?

Answer 10

Balanced translocations normally do not cause any abnormal phenotype. Unbalanced translocations can result in miscarriage, stillbirth, and chromosomal imbalance (i.e. trisomies) (p.88)

Question 11

What is the genetic mutation associated with Cri-du-Chat syndrome?

Answer 11

Congenital microdeletion of short arm of chromosome 5; (46XX or XY, 5p-) (p.89)

Question 12

What are the typical clinical findings in a patient with Cri-du-chat syndrome?

Answer 12

Microcephaly, moderate to severe mental retardation, high pitched crying/mewing, epicanthal folds, cardiac abnormalities (VSD) (p.89)

Question 13

What is the genetic mutation associated with Williams syndrome?

Answer 13

Congenital microdeletion of the long arm of chromosome 7 (deleted region includes the elastin gene) (p.89)

Question 14

What are the typical clinical findings in a patient with Williams syndrome?

Answer 14

Elfin’ facies, intellectual disability, hypercalcemia, (increased sensitivity to vitamin D), well developed verbal skills, extreme friendliness with strangers, cardiovascular problems (p.89)

Question 15

Name the two 22q11 deletion syndromes.

Answer 15

DiGeorge syndrome; Velocardiofacial syndrome (p.89)

Question 16

Describe the presentation of patients with 22q11 deletion syndromes.

Answer 16

Variable presentation including cleft palate, abnormal facies, thymic aplasia (T-cell deficiency), cardiac defects, hypocalcemia secondary to parathyroid aplasia (CATCH-22) (p.89)

Question 17

What is the cause of 22q11 deletion syndromes?

Answer 17

Aberrant development of the 3rd and 4th branchial pouches (p.89)

Question 18

What is the difference between DiGeorge syndrome and Velocardiofacial syndromes?

Answer 18

DiGeorge- thymic, parathyroid, and cardiac defects; velocardiofacial syndrome- palate, facial, cardiac defects (p.89)