Population cytogenetics, assignment of gene loci in autosomes, karyotype-phenotype correlations. A progress report on human cytogenetics.

Abstract

This review summarizes three areas of human cytogenetics: 1. Studies of over 10,000 unselected live-born infants from four different series reveal an incidence of chromosomal aberrations of 1:200. About 50% of anomalies involve the chromosome structure; abnormalities of the sex chromosomes and the autosomes occur with equal frequency; about 50% of infants with a chromosomal aberration are clinically inapparent. The most frequent numerical anomalies are the XXY- and the XYY-condition, and the most frequent structural aberration is the translocation DqDq between two chromosomes of group D. According to work of Lubs and Ruddle, minor variants of the normal karyotype occur in the different chromosomal groups with following frequencies: A-group: 1.1%, B-group: 0.04%, C-group: 0.16%, D-group: 16.9%, E-group: 4.2%, F-group: 0.08%, G-group: 6.2%, Y-chromosome: 5.6%. Recent studies of the familial translocation DqGq disclose a smaller than expected risk for trisomie offspring to translocation heterozygotes: about 15–18% for female and 2–3% for male carries of this translocation. 2. Several studies concerning the assignment of gene loci to autosomes are reviewed. At present, the following genes could be assigned to human autosomes with varying degrees of certainty: (I) Duffy blood group and congenital zonular pulverent cataract on or near the proximal long arm of chromosome 1; (II) MN locus on chromosome 4 (distal long arm) or chromosome 2 (middle of long arm); (III) Gc factor on chromosome 4 or 19\2-20; (IV) Hageman blood clotting factor on the short arm of chromsome 6; (V) Haptoglobin alpha chain locus on chromosome 16; (VI) thymidine kinase locus on a chromosome 17 or 18. In addition, there are some as yet inconclusive data supporting a possible association of the erythrocyte acid phosphatase and chromosome 2; triosephosphate isomerase and the short arm of chromosome 5; chromosome 18 and immunoglobulin A production; chromosome 21 and the Lewis red cell antigen (a). It is emphasized that nearly all of these assignments must be considered tentative. 3. Probably three further deletion syndromes could now be recognized clinically: (I) The partial deletion of the short arm of chromosome 18 (18p-), (II) patients with a ring-D(? 14) chromosome, and (III) patients with a partial deletion of the long arm of chromosome 13.