Chromosome Abnormalities

Question 1

Down Syndrome

Answer 1

caused by trisomy 21 (95%) or a Robertsonian translocation with 13 and 14 (5%)

1 in 600 live births

Question 2

characteristics of Down Syndrome

Answer 2

children exhibit hypotonia, open mouth, protruding toungue, mental retardation

also have brachycephaly, flat occiput, upward slanting palpebral fissures, epicanthal folds, brushfield spots

short fingers, single flexion crease, brachymesophalangia, transverse palmar crease

wide gap between first and second toes, CV and gastrointestinal issues, genitourinary defects

Question 3

common Down Syndrome cardiac defect

Answer 3

AV canal or Endocardial cushion defect - communication between all 4 chambers

Question 4

meiotic nondisjunction

Answer 4

results in trisomic and monosomic zygotes, most common form of chromosome rearrangement

Question 5

trisomy 13

Answer 5

1 in 5,000 births

malformations found in >50% of cases

Question 6

characteristics of trisomy 13

Answer 6

scalp defects, microcephaly, sloping forehead, wide sutures, large fontanelles, microphthalmia (small eyes), colobomata of iris, retinal dysplasia

transverse palmar crease, camptodactyly, post-axial polydactyly, prominent heels

cardiact problems, cryptorchidism, bicornuate uterus, hemangiomas

82% mortality by 12 months

Question 7

trisomy 18

Answer 7

1 in 3000 live births, malformations found in >50% of cases

Question 8

characteristics of trisomy 18

Answer 8

polyhydramnios, small placenta, single umbilical artery

small for gestational age, altered timing, hyploplasia of muscle and subcutaneous tissue

severe mental retardation, craniofacial malformities, clenched hand, overlapping fingers, absent of flexion crease on 5th finger

cardiac defects, cryptorchidism, mild hirsutism

90% mortality by 12 months

Question 9

Turner Syndrome

Answer 9

1 in 2500 females, short stature, mean IQ, poor motor skills, poor visual-spatial organization, poor social cognition

failure to develop secondary sex characteristics at puberty, sterile

caused by lack of an X chromosome

Question 10

characteristics of Turner Syndrome

Answer 10

short stature, epicanthal folds, abnormal ears, low hairline, redundant skin, webbed neck

edema of hands and feet, short 4th metacarpal and metatarsal, narrow, hyperconvex nails

borad chest, widely spaced nipples, cardiac defects, coarctation of aorta, hearing impairment, horseshoe kidney

Question 11

William’s Syndrome

Answer 11

loss of 7q11.23, microdeletion

distinctive facies, locquacious personality, mental retardation, hypercalcemia, supravalvular aortic stenosis

Question 12

Kleinfelter Syndrome

Answer 12

47, XXY, but can have more copies of X

characteristics include small testes after puberty, infertility, poorly developed secondary sexual characteristics, tall and thin

greater number of X chromosomes leads to greater degree of abnormality

Question 13

XYY syndrome

Answer 13

1 in 1000 male births, may be associated with high incidence of aggression

above average height