Autosomal dominant Charcot-Marie-Tooth disease type 1A and hereditary neuropathy with liability to pressure palsies: detection of the recombination in Slovene patients and exclusion of the potentially recessive Thr118Met PMP22 point mutation

Charcot-Marie-Tooth disease type 1 (CMT1) and hereditary neuropathy with liability to pressure palsies (HNPP) are the most frequent autosomal dominantly inherited disorders of the peripheral nervous system. The recessive inheritance is observed only exceptionally. Unequal crossing-over of misaligned flanking CMT1A-REP elements on chromosome 17p11.2 is the most frequent cause of the CMT1A duplication and of the reciprocal deletion in HNPP patients. Recently a recombination was noted. In our study 71 Slovene CMT1 patients from 36 families, 12 HNPP patients from 6 families and their 31 healthy relatives were analysed for the presence of these recombination mutations. In 29 of 36 unrelated CMT1 (81%) and in all 6 unrelated HNPP patients the duplication or the deletion, on chromosome 17p11.2-12 was detected. In 26 out of 29 duplication patients (CMT1A) (90%) a 3.2 kb EcoRI/SacI duplication junction fragment was observed. The analogous 7.8 kb EcoRI/EcoRI deletion junction fragment was found in 4 out of 6 unrelated HNPP deletion patients (67%). Overall we found a recombination mutation inside the in 86% of unrelated Slovene CMT1A and HNPP patients. One hundred and thirty-six DNA samples of the CMT1 and HNPP patients and of the healthy controls were negative for the potentially recessive Thr118Met PMP22 amino acid substitution. Dominantly inherited CMT1A duplications and HNPP deletions on chromosome 17p11.2 are thus, as in most other European countries, the most common mutations in Slovene CMT1 and HNPP patients. No signs of polymorphism or of potentially recessive mutation were found at the specific Thr118Met PMP22 site.

Rapid DNA-based prenatal diagnosis by genetic linkage in three families with Alport's syndrome

Alport's syndrome (AS) is a clinically and genetically heterogeneous progressive inherited glomerulonephritis characterized by hematuria, sensorineural hearing loss, ocular lesions, and specific alterations of the glomerular basement membrane. Typically, AS shows an X-linked dominant pattern of inheritance, with mutations affecting the collagen type IV alpha5 chain gene (COL4A5) at Xq22. Rarely, AS is caused in some families by mutations of the COL4A3/A4 genes on chromosome 2q, showing an autosomal recessive transmission. Very few families have been described with possible autosomal dominant AS, but no mutations in any of the COL4 genes have been found. We describe three unrelated families affected with a severe AS phenotype in which DNA-based prenatal diagnosis by linkage analysis was made in fetuses at risk for the disease. In two families, the pedigree structure and the clinical picture were consistent with typical X-linked dominant AS. In these families, autosomal inheritance was also ruled out molecularly. In one family, despite careful clinical and molecular evaluation, the mode of transmission could not be firmly established. We used tightly linked and intragenic COL4A5 markers, as well as COL4A3/A4-linked markers. A chromosome Y-specific marker for fetal sex determination was simultaneously used. In all the families, before the fetal analysis, the putative at-risk X haplotype was identified with high diagnostic accuracy. We diagnosed a healthy male fetus in one family, and female but carrier fetuses in the other two kindreds, who decided not to terminate their pregnancies. We used rapid nonisotopic polymerase chain reaction-based methods, and the results were available within 2 to 3 days. The genetic results significantly affected the reproductive decisions of the parents. This report illustrates the application of genetic linkage analysis as an additional tool for molecular diagnosis in AS, and also addresses the issue of the attitudes of the families toward prenatal testing. To our knowledge, prenatal diagnosis of AS using a genetic linkage approach has not been previously reported.

Genetic epidemiology of myotonic dystrophy in Istria, Croatia

OBJECTIVES

We evaluated epidemiology of myotonic dystrophy in Istria, Croatia including direct mutation analysis as an additional, specific diagnostic criterion.

MATERIAL AND METHODS

Patients were ascertained in the period 1980-1994 from multiple sources under established clinical criteria with a special reference to congenital and minimal forms of the disease. Additionally, patients and their relatives were evaluated by direct mutation analysis. The prevalence, corrected for underascertainment, was estimated on July 1, 1989.

RESULTS

A total of 33 DM patients from nine families were ascertained. In all families the diagnosis was confirmed by mutation analysis of the DM gene. After correction for underascertainment the prevalence of 18.1/100,000 was calculated.

CONCLUSION

One of the highest prevalence estimates of DM in the populations without evidence of founder effect or genetic isolation was found. Our results imply the importance of ascertainment of patients with all forms of DM and utilization of specific diagnostic tests for estimation of genetic epidemiology in DM.

Loss of heterozygosity at 7q31 in breast cancer: results from an International Collaborative Study Group. The Breast Cancer Somatic Genetics Consortium

Loss of heterozygosity (LOH) at 7q31 has been claimed to occur in over 80% of all breast cancers and to be of prognostic significance. This would make this genetic alteration the most common event observed in breast cancer to date. Others, however, have been unable to confirm this high incidence. In this multicenter study, we have complied LOH scorings for three polymorphic markers for 7q31-q32 in 683 breast tumors. Although some significant differences between centers existed, no center reported more than 40% LOH, and the average rate was 19%. Disease-free and overall survival of the patients whose tumors carried LOH at 7q31 did not differ significantly from those patients whose tumors showed retention of heterozygosity at 7q31. In a double-blind scoring of a subset of the raw data, an average discordant rate of LOH scoring of 12% was observed. While startling in itself, this was unable to explain the variation among centers, nor the difference with the initially reported high rate of LOH. We conclude that LOH at 7q31 is not important as a genetic alteration in breast cancer as originally suggested, nor a strong determinant of disease outcome.

Genetic epidemiology of Duchenne and Becker muscular dystrophy in Slovenia

Most population studies on Duchenne (DMD) and Becker (BMD) muscular dystrophies predated the discovery of the gene and its product dystrophin. The diagnosis of these conditions and consequent epidemiological estimates were therefore limited to clinical criteria. In our study of the Slovene population the prevalence and cumulative incidence of DMD and BMD were calculated by including additional diagnostic tests: deletion screening in the dystrophin gene as well as dystrophin immunocytochemistry. The minimal prevalence rates, 2.9/100,000 for DMD, 1.2/100,000 for BMD, and the minimal cumulative DMD incidence rate of 13.8/100,000 are in the range of lower estimates compared to studies world-wide. However, we found a high BMD cumulative incidence rate of 5.7/100,000 and a high proportion of BMD versus DMD cumulative incidence rate (41.3%). Our results imply that the epidemiological figures for BMD might have been underestimated in the past.

Correlations between clinical, electrophysiological and genetic findings in hereditary motor and sensory neuropathy type I (HMSN I)

We evaluated the correlation between clinical signs, electrophysiological data and molecular genetics findings in patients with HMSN I. We found a duplication in the PMP-22 gene in 60% of HMSN I families. We compared clinical and electrophysiological data between 23 patients with duplication and 18 patients without duplication. No statistically significant differences in age of onset of symptoms, clinical signs and electrophysiological parameters were found.

I/D polymorphism at the locus for ACE and apo A-I gene promoter polymorphism as risk factors for coronary artery disease in patients with familial hypercholesterolemia

In our study we searched for an association between the insertion/deletion (I/D) polymorphism at the ACE locus as well as apo A-I promoter polymorphism and coronary artery disease (CAD) in patients with familial hypercholesterolemia (FH). 34 FH patients over 40 years were ascertained; 16 patients with CAD were compared with 18 patients without CAD. There was an excess of DD or ID genotype in FH patients with CAD (OR = 4.9, CI = 1.17-22.17; Fisher exact p = 0.012), however, no association between G to A substitution in the promoter region of the apo A-I gene and CAD was found. Our results suggest that the DD/ID genotype at the ACE gene locus might be an important genetic risk factor for CAD in FH patients.

CTG repeat analysis in lymphocytes, muscles and fibroblasts in patients with myotonic dystrophy

The mutation responsible for DM has been identified as the amplification of a polymorphic (CTG)n repeat in the 3' untranslated region of the myotonin proteinase gene. To examine somatic instability of the repeat, we studied tissue variability of the CTG expansion of three mesodermally derived tissues: lymphocytes, cultured fibroblasts and muscle cells. In six patients with adult onset DM, the repeat region was larger in skeletal muscles and fibrolasts as compared to lymphocytes. Our findings indicate that somatic CTG instability between examined tissues might take place postnatally by a selection mechanism in lymphocytes.

The gene for the familial form of incontinentia pigmenti (IP2) maps to the distal part of Xq28

Linkage data for familial incontinentia pigmenti (IP2) and 17 X chromosomal markers are reported. The linkage previously found between IP2 and the F8C locus is confirmed (Z max = 11.85 at theta = 0.028). Linkage is established with distal markers DXS1108 (Z max = 10.06 at theta = 0.00) and DXYS154 (Z = 9.07 at theta = 0.019). Multipoint analysis supports the distal localization of the IP2 gene with respect to the F8C locus.

An irradiation-reduced hybrid panel for fine-structure mapping of the Xq28 region in the human genome

Irradiation-reduced somatic cell hybrids containing fragments of the human X chromosome were constructed. Analysis of 16 hybrids that retained the Xq28 region with 12 Xq28-specific markers identified at least six different breakpoints, supporting the order cen-DXS304-DXS374-(DXS33, DXS134, DXS52, DXS15)-RCP-(DXS254, G6PD, F8C)-(DXS115, DXYS64)-qter. The generated panel of hybrids provides a useful tool for fine mapping of probes in the Xq28 region.

Prevalence of retinitis pigmentosa in Slovenia

Two hundred and twenty-nine symptomatic patients with retinitis pigmentosa were ascertained in Slovenia between 1986 and 1990. Twenty-three further patients were identified while data from 63 families (82 patients) were being collected. After correction for underascertainment, a prevalence of 1 in 6023 was estimated in the Slovene population (1,999,477 in 1990). The highest prevalence of 1 in 1902 was found in the age group 65 years and older. Of 63 analysed families, 17 (27%) showed autosomal dominant, 13 (21%) autosomal recessive, and one family (1.5%) X-linked inheritance; in 30 families (47.5%) isolated cases were found; and in two families the mode of inheritance was impossible to determine.