Molecular genetics of human blue cone monochromacy

Blue cone monochromacy is a rare X-linked disorder of color vision characterized by the absence of both red and green cone sensitivities. In 12 of 12 families carrying this trait, alterations are observed in the red and green visual pigment gene cluster. The alterations fall into two classes. One class arose from the wild type by a two-step pathway consisting of unequal homologous recombination and point mutation. The second class arose by nonhomologous deletion of genomic DNA adjacent to the red and green pigment gene cluster. These deletions define a 579-base pair region that is located 4 kilobases upstream of the red pigment gene and 43 kilobases upstream of the nearest green pigment gene; this 579-base pair region is essential for the activity of both pigment genes.

Parental origin of the extra chromosome in the cat eye syndrome: evidence from heteromorphism and in situ hybridization analysis

Two individuals, a boy and girl, with a clinical diagnosis of cat eye syndrome had an extra bisatellited chromosome. In the girl, the diagnosis was made on the basis of coloboma of the right iris, right preauricular pit, and imperforate anus; in the boy, bilateral colobomata of the iris, down-slanting palpebral fissures, right preauricular skin tag, and right preauricular pit. Multiple staining techniques were used to characterize the extra chromosomes. With G-banding the extra chromosome usually appeared monocentric with two major G-positive bands, but with satellites on both ends; with C-banding, two C-band positive regions were evident, indicating that the chromosomes were likely dicentric. Silver staining demonstrated the presence of NORs near each end; Q-banding showed satellites on each end, differing in brightness and size. The chromosomes of the parents were normal; comparisons of Q-band heteromorphisms of the acrocentric chromosomes of the parents with those of the extra chromosome showed in each case one short arm/satellite region of the extra chromosome identical in appearance to one chromosome 22 of the mother and the other end of the extra bisatellited chromosome identical to the short arm/satellite of the mother's second chromosome 22. This extra chromosome, then, is the result of a maternal meiotic error in each case. In situ hybridization studies using the chromosome 22-derived probe p22/34, which identifies locus D22S9, showed 16% of the cells from the female patient to have silver grains on the proximal long arm of the normal chromosome 22 and 14% on the extra chromosome, while 10% of cells from the male had grains on the normal chromosomes 22 and an equal number on the extra chromosome, confirming the chromosome 22 origin of the extra chromosome in these patients.

Serum IgM in retinitis pigmentosa: a genetic study

Because of a published report that serum immunoglobulin M (IgM) was elevated in some cases of retinitis pigmentosa (RP), a genetic study was undertaken to determine if a particular pattern of inheritance was associated with elevated IgM. Seventy-five RP patients in 37 families were ascertained and classified by pattern of inheritance into six groups. Serum IgM was quantitated by the radial immunodiffusion technique. Fifty-one controls were also studied. Methods of adjusting the IgM values for sex, age, and race were derived, but only a sex adjustment was used, since no effect of age on IgM was found in this sample, and there were few data on race. There was no signifcant difference in mean IgM levels between RP patients and controls. The variance of the RP group was slightly greater than that of the controls. One-way analysis of variance of the six genetic categories of RP and controls was performed on the raw data and on the data after log transformation. The F-ratio was not significant, indicating that there was no difference in serum IgM levels among the seven groups. Possible reasons for the discrepancy in results between this study and the previous report are presented.