Direct duplication of 8p21.3-->p23.1: a cytogenetic anomaly associated with developmental delay without consistent clinical features.

We report six cases in two families and a sporadic case with a direct duplication of region 8p21.3-->23.1. In one family, the duplication started in the mother and was transmitted to one son and one daughter. In the second family, the father was mosaic for the anomaly that was transmitted to his two daughters. The cytogenetic anomaly was initially described as an 8p+ with banding analysis and then delineated with fluorescence in situ hybridization (FISH) using whole-chromosome 8 painting, 8p specific painting, and 8p or 8p/8q subtelomeric probes. Deletion was not detected in the subtelomeric region of the abnormal chromosome 8 examined in one family and in the sporadic case. The phenotypic picture varies from normal to moderate mental retardation in the affected individuals. No consistent minor anomalies or congenital defects were observed among these cases. After comparing the chromosome region involved in our cases with those in others having direct or inverted duplications of 8p, it is thought that the segment 8p21.1-->21.3 might be the critical region for an 8p duplication syndrome. The parental origin of the duplication does not seem to impact its clinical significance.

Sister-chromatid exchange in highly purified human CD4+ and CD8+ lymphocytes.

Sister-chromatid exchange (SCE) frequencies were determined in human peripheral blood CD4+ and CD8+ T lymphocyte subpopulations which were rapidly and highly purified from pooled T lymphocytes by immunological methods. The purified lymphocytes were stimulated with phytohemagglutinin (PHA) for 4 days. CD4+ lymphocytes showed significantly higher SCE frequencies than autologous CD8+ lymphocytes when measured simultaneously after identical bromodeoxyuridine (BrdU) incubation times. Differences in SCE frequencies between CD4+ and CD8+ lymphocytes were also detected when mitomycin C (MMC) was added to the cultures. Higher SCE frequencies in CD4+ lymphocytes were associated with lower proliferating rate indices (PRI) as compared to autologous CD8+ lymphocytes. Abnormalities in CD4+ T lymphocyte function and number in peripheral blood have been observed in several diseases characterized by immunological disorders. Thus, our data may suggest a link between some immunological disturbances and abnormal SCE frequencies in T lymphocyte subsets.

Twinning and mitotic crossing-over: some possibilities and their implications.

Mitotic crossing-over does occur in man and is much more frequent and important than generally assumed. Its postzygotic occurrence before an embryo differentiates into MZ twins is theoretically predicted to have disrupting effects on genomic imprinting and cis-acting sequences, with consequences ranging from early lethality to MZ twin discordance. Some predictions are at odds with classical views on twinning and include a high discordance rate of MZ twins for some genetic diseases. A review of MZ twin discordance and an attempt at explaining some of the data lead one to hypothesize both the existence of a sex differences in the rate of mitotic crossing-over and the impossibility for crossed X chromosomes to undergo inactivation. The close interrelationship of twinning and midline malformations further suggests a major role of mitotic crossing-over in the induction of the twinning process itself. The model can be tested with molecular methods and provides a new approach for the gene mapping of so-called multifactorial diseases and of rarer disorders with apparently irregular inheritance.

The cis-configuration effects of rare chromosomal fragile sites.

Rare chromosomal fragile sites may adversely affect specific alleles of closely linked genes when in cis-configuration. This is illustrated by data published in Sutherland & Hecht (1985) on chromosome 16 at band q22.1.

Wilms' tumour and related syndromes. A unifying theory.

The major role of somatic crossing-over in the aetiology of Wilms' tumour and other forms of cancer is emphasized. A model is proposed to show that tumour development is due to a cis-trans disruptive effect of somatic crossing-over on the maintenance of differential parental imprinting.

[Hereditary juvenile dystrophy of the macula in a large family from Epirus]. / Dystrophie héréditaire juvénile de la macula chez une famille nombreuse d'Epire.

The authors present a clinical, epidemiologic and genetic study of juvenile macular dystrophy (Stargardt's disease) in a large kindred from Epirus in Greece. The family tree consists of 372 individuals spanning six generations over more than a century. 257 are direct descendants of the founding couple. Nineteen individuals were found to suffer from Stargardt's disease, thirteen of whom are still alive today. Segregation analysis of the data showed that in this pedigree, the disease is transmitted with the autosomal dominant mode of inheritance.

The cis-trans effects of crossing-over on the penetrance and expressivity of dominantly inherited disorders.

A surprisingly simple model based on the cis-trans effects of meiotic and mitotic crossing-over is proposed to explain apparent non-penetrance and reduced expressivity in dominantly inherited disorders. Sex differences, discordant monozygotic twins, multifactorial inheritance and allelism are also discussed.

Hypothyroidism and sex chromosomes.

The observation of Campbell and Price in 1979 that their Unit had diagnosed four subjects with both Klinefelter's syndrome and congenital hypothyroidism raised the suspicion of an association between the two conditions. This, and the published reports of an XX male, five XXY males, and one mosaic XY/XXY with congenital or acquired forms of hypothyroidism, together with the higher incidence in women and the absence of sex difference among inherited congenital cases, suggested a possible sex chromosome effect in the aetiology of sporadic hypothyroidism. Various hypotheses can be tested either by examining the frequency of hypothyroidism in sex chromatin positive males or by establishing a higher frequency of sex chromatin positive males among hypothyroid cases than in normal males. We examined 57 boys with hypothyroidism for the presence of sex chromatin and found all to be negative. From this relatively small sample we can only exclude the possibility of a very large (100 fold) difference in frequency between the two populations and therefore more data are needed.

The effects of severe mixed environmental pollution on human chromosomes.

Cytogenetic studies were conducted on healthy young mothers, shortly after child birth, in two residential areas each with an approximate population of 20,000, situated about 25 km from Athens, Greece. One of the areas, Elefsis, is subject to severe mixed industrial pollution, and the other, Koropi, is relatively free of pollution. Chromosomal aberrations were investigated in 16 women from each area in 72 hour lymphocyte cultures treated with gentian violet to enhance any chromosomal instability induced by the pollution. The women were of a comparable socioeconomic level, aged between 20 and 31 years, and with no history of factors associated with mutagenesis. Venous blood samples were taken from the two groups and processed concurrently. The slides were coded and examined independently by two observers, who were unaware of the source of the samples. A total of 100 cells was examined on each sample. The two observers obtained highly comparable results. Women from Elefsis had an average of 0.42 anomalies per cell and those from Koropi had 0.39. The absence of a statistically significant difference between the two groups clearly shows that the severe mixed environmental pollution of Elefsis has no significant visible effect on human chromosomes in most residents. However, two Elefsis women had abnormal results and could be at risk. Their presence is not sufficient to raise significantly their group's average, but the induction by pollution of an increased rate of chromosomal anomalies in only a few people at risk could account for the known association between urban residence and cancer mortality.