Rapid procedures for prenatal diagnosis of Cockayne syndrome

Ethnic variation in vitamin D-binding protein (GC): a review of isoelectric focusing studies in human populations

Since the discovery in 1977 that the GC1 gene could be resolved into two common subcomponents on an isoelectric focusing (IEF) gel, a large number of ethnic groups have been screened to analyze the extent of genetic variation in human populations. Using the IEF technique, approximately 50,000 individuals from 160 different populations have been tested for the GC polymorphism. A marked variation in common GC suballele frequencies in different geographic areas seems to correlate with skin pigmentation and intensity of sun light. Pigmented (black) and keratinized (yellowish) skin type populations have a relatively high frequency of the GC*IF allele as compared to white skin populations. By comparison non-pigmented and non-keratinized white skin populations are generally characterized by having the maximum values of the GC*IS allele. The anthropologic significance of the GC locus has been enhanced further by detecting additional unique GC variants which provide useful information about evolutionary links between different populations. However, the presence of some electrophoretically identical unique variants in genetically and geographically distinct populations demand further investigation of these allelic variants to shed more light on their origins.

Human DNA repair defects

A number of human genetic diseases have come to be described as being defective in DNA repair. The minimum criterion on which this assignment is based is hypersensitivity to the clastogenic or lethal action of specific DNA damaging agents. In one disease, xeroderma pigmentosum, the molecular evidence for a defect in DNA repair is unequivocal. This condition then acts as a model for dissecting others. For the other diseases the formal evidence for defects in repair is less secure or even lacking. The evidence for repair in each disease is assembled together with any methods that have been used to support the differential diagnosis or for prenatal diagnosis. Attempts to clone human DNA repair genes are in hand and may provide the necessary evidence to decide if all the putative DNA repair defective diseases are genuine. Neoplastic disease and neurological degeneration together with immune defects are frequent clinical features linking this set of diseases, suggesting that effective DNA repair may be important in many aspects of human health.

Prenatal diagnosis of Cockayne's syndrome

Cockayne's syndrome (CS) was diagnosed prenatally by examination of amniotic cells cultured in vitro. RNA synthesis after irradiation with ultraviolet light was abnormal in cells from a fetus with CS but not in cells from a fetus which was normal. The procedure is simple and rapid and the outcome of the test in two cases (one positive, one negative) was unambiguous.