SBD L51
CLINICAL CYTOGENETICS & CHROMOSOME DISORDERS
27/03/2000
DR CAMPBELL

A six sided handout was given at the lecture, which is available here.

CLINICAL CYTOGENETICS:

prenatal bloods
prenatal: amniotic fluid, chorionic villus, foetal blood
solid tissues
leukaemias (bone marrow and blood)

HOW COMMON ARE CHROMOSOME ABNORMALITIES?:
- depends on the population being studied.

Spontaneous abortion (mainly in the first trimester) - approximately 50% are chomosomally abnormal
still birth - approximately 5% are chromosomally abnormal
live birth - approximately 0.5% are chromosomally abnormal

75% of Down’s babies are lost in utero.

TRANSLOCATION - Robertsonian/Reciprocal

Non-disjunction of meiosis I:

leaves nullisonic gamete (n=22)
also leaves an n=23

Down’s, Klinefelters, Patau - 23 + 24 = 47
Turner’s - 22 + 23 = 45

Non-disjunction of meiosis II:
gives n=47 or 45 again.

DOWN’S DYSMORPHOLOGY:
short stature, brachycephaly and flat occiput, clinodactyly (5th finger curving), single palmar creases, sandal gap (1st and 2nd toes), brushfield spots, small low-set ears, large protruding tongue, mental impairment, heart abnormalities, duodenal atresia, kidney abnormalities, echogenic bowel, up-slanting palpebral fissures, permanent ageing in some, early onset of Alzheimer’s.