Myosin VIIA gene: heterogeneity of the mutations responsible for Usher syndrome type IB

Usher syndrome is recognized as the most frequent cause of hereditary deaf-blindness. Usher syndrome type I (USH1), the most severe form of the disease, is characterized by profound congenital sensorineural deafness, constant vestibular dysfunction, and retinitis pigmentosa of prepubertal onset. This form is genetically heterogeneous and five loci (USH1A-E) have been mapped thusfar. However, only the gene responsible for USH1 B (which accounts for approximately 75% of USH1 cases) has been characterized. It encodes a long-tailed unconventional myosin, myosin VIIA, with a predicted 2215 amino acid sequence. Primers covering the complete myosin VIIA coding sequence as well as the 3' non coding sequence were designed, allowing direct sequence analysis of each of the 48 coding exons and flanking splice sites in seven patients affected by USH1. Four novel mutations were thereby identified. The possibility should now be considered of a sequence-based prenatal diagnosis in some of the families affected by this very severe form of Usher syndrome.      

The GAP-related domain of tuberin, the product of the TSC2 gene, is a target for missense mutations in tuberous sclerosis

Tuberous sclerosis is an autosomal dominant trait in which the dysregulation of cellular proliferation and differentiation results in the development of hamartomatous growths in many organs. The TSC2 gene is one of two genes determining tuberous sclerosis. Inactivating germline mutations of TSC2 in patients with tuberous sclerosis and somatic loss of heterozygosity at the TSC2 locus in the associated hamartomas indicate that TSC2 functions as a tumour suppressor gene and that loss of function is critical to expression of the tuberous sclerosis phenotype. The TSC2 product, tuberin, has a region of homology with the GTPase activating protein rap1GAP and stimulates the GTPase activity of rap1a and rab5a in vitro. Here we show that the region of homology between tuberin and human rap1GAP and the murine GAP mSpa1 is more extensive than previously reported and spans approximately 160 amino acid residues encoded within exons 34-38 of the TSC2 gene. Single strand conformation polymorphism analysis of these exons in 173 unrelated patients with tuberous sclerosis and direct sequencing of variant conformers together with study of additional family members enabled characterisation of disease associated mutations in 14 cases. Missense mutations, which occurred in exons 36, 37 and 38 were identified in eight cases, four of whom shared the same recurrent change P1675L. Each of the five different missense mutations identified was shown to occur de novo in at least one sporadic case of tuberous sclerosis. The high proportion of missense mutations detected in the region of the TSC2 gene encoding the GAP-related domain supports its key role in the regulation of cellular growth.      

Genetic linkage of a novel autosomal dominant restrictive cardiomyopathy locus

Background: In recent years, non-syndromic idiopathic cardiomyopathies have increasingly been characterised as autosomal dominant conditions caused by single gene mutations. Loci have been identified for hypertrophic and dilated cardiomyopathy, and in some cases the same loci are associated with restrictive cardiomyopathy (RCM). In a kindred with RCM that we previously reported, we ruled out the known cardiomyopathy loci and other candidate genes by linkage analysis and mutation screening. Methods and Results: Here we report a genome-wide analysis in this family that has resulted in linkage to a region on chromosome 10. Conclusions: There are no genes in the interval that are known to cause idiopathic cardiomyopathy, and thus this linkage represents localisation of a new RCM locus.     

An Association Between a Microsatellite Polymorphism at the DRD5 Gene and the Liability to Substance Abuse: Pilot Study

We have conducted a population-based association study of substance abuse and a microsatellite at the dopamine D5 receptor locus (DRD5) in a sample of European–American males and females with substance dependence (SA) or without any psychiatric disorder. Overrepresentation of the most frequent allele (148 bp) was found in males in the SA group (OR = 2.2, P= .02); this finding was reproduced in females (OR = 5.4, p< .001). The difference in the frequencies of this allele between SA males and SA females was statistically significant. The genotype coded in accordance with the dose of this allele correlated with substance abuse liability in males and females (stronger in females) and with novelty seeking in females. There was no evidence of correlation between the genotypes of spouses that could be induced by assortative mating for the liability to substance abuse. The data suggest that the DRD5 locus is involved in the variation and sex dimorphism of substance abuse liability.CEDAR is a consortium between St. Francis Medical Center and the University of Pittsburgh.     

Formaldehyde in cryoprotectant propanediol and effect on mouse zygotes

Cryopreservation of human zygotes and embryos has been routinely performed by in-vitro fertilization clinics for many years. Karran and Legge (1996) first reported that formaldehyde (FA) present in the cryoprotective solutions can have a deleterious effect on mouse oocytes. FA is a cytotoxic, carcinogenic and mutagenic chemical. The effect of FA on mouse zygotes was investigated. In addition, the concentrations of FA in propanediol (PROH) obtained from various sources were determined. Pooled 1-cell embryos were dispensed into droplets of modified Ham's F10 or human tubal fluid containing various concentrations of FA. Since bovine serum albumin (BSA) may minimize toxicity additional trials were done as above in the absence of BSA. FA concentration in the standard 1.5 M PROH, from different sources in water, was measured in the same assay using a standard curve of 0-100 microM FA. FA in a complex medium had a significant deleterious effect on embryo development and hatching but only at 1 mM concentration (P < 0.000001; see Tables I-III). There was no significant effect of FA at 100 microM. However, in a simple medium even 50 microM FA decreased embryo hatching. FA was present in 1.5 M PROH from different sources (range 1.0-35.3 microM concentration). It appears that FA concentrations do not increase with storage because FA concentrations were low even after opening and storage for 3 years on the shelf. This suggests that FA is a contaminant during the manufacturing process and may vary from manufacturer to manufacturer and batch to batch. Until further studies are done to confirm the lack of toxicity to embryos during cryopreservation (with or without FA scavengers) it may be prudent to screen all batches of cryoprotectants for FA as part of quality control.      

Familial Similarities of Changes in Cognitive, Behavioral, and Physiological Variables in a Cardiovascular Health Promotion Program

A number of studies have demonstrated that physiological andbehavioral cardiovascular disease (CVD) risk factors aggregatewithin families. This fact, and the potential mediating rolethat the family plays in behavior change, have led to the developmentof family-based CVD risk reduction programs, including the SanDiego Family Health Project. The aggregation of behavioral,physiological, and cognitive changes within families was assessedduring a 1-year intervention. We found evidence of modest butsignificant aggregation of change. There was more aggregationof change in behavioral variables than in physiological or cognitivevariables. More significant correlations were found among 3-dayfood record measures than among 24-hour recall dietary measures,suggesting an influence of assessment method. Aggregation ofchange within families was stronger within generations thanacross generations. These data point to the importance of involvingall age groups in health promotion programs.     

Variable expression of autosomal recessive polycystic kidney disease and congenital hepatic fibrosis within a family

Blyth and Ockenden [1971] assigned patients with autosomal recessive polycystic kidney disease (ARPCKD) to 4 discrete groups (perinatal, neonatal, infantile, juvenile) on the basis of the age of presentation. They and others speculated that at least 4 genes were responsible for what they considered to be closely related, but different conditions. These views have gained wide but not universal acceptance. Some workers have insisted that the perinatal and neonatal "forms" of ARPCKD differ fundamentally from the juvenile "form." However, others have proposed that ARPCKD-CHF (congenital hepatic fibrosis) and CHF-ARPCKD are manifestations of the same disease with variation of expression in a kindred. We report on a patient who presented at birth (1979) with ARPCKD and respiratory distress. He died at 18 hr. An older sib presented at 16 yr in 1984. She had no symptoms, but her mother wanted reassurance that the daughter did not have a condition similar to that of the deceased sib. Blood pressure was 120/80 mm Hg and there was hepatosplenomegaly. A diagnosis of renal tubular ectasia and CHF was made by ultrasonography, radiologic studies, and a liver biopsy. The evidence from families such as this favors the concept that ARPCKD and CHF presenting as Blyth and Ockenden's perinatal form, and CHF and renal tubular ectasia as their juvenile form, are manifestations of the same genetic disorder, and that the different manifestations are more likely variations in expression than the results of different mutant genes. The manifestations in this family add weight to the growing body of evidence that intrafamilial variability may occur, not only in autosomal dominant conditions, but also in autosomal recessive disorders.