[Mutation analysis in the CTG-base multiplication in a family with myotonic dystrophy in three generations]

A PCR-based method with a novel silver staining detection was developed for the determination of CTG repeat number in the 3' untranslated region of the MD-PK gene responsible for myotonic dystrophy. Through the investigation of a family with affected members in three generations the application of the method is presented. According to the results, healthy individuals were verified easily, and the repeat number in patients with mild features or with premutation could be determined accurately. In severe clinical forms, e.g. congenital myopathy, the expansion can be deduced only from the lack of amplification, however, this is also helpful if the segregation of familial alleles is known.

Phenotype of the Williams-Beuren syndrome associated with hemizygosity at the elastin locus

To correlate presence or absence of a 7q11 microdeletion with the clinical picture of the Williams-Beuren syndrome (WBS), we investigated 29 patients with a clinical diagnosis of WBS or WBS-like features, aged 1-30 years, using molecular analysis and/or fluorescent in situ hybridization (FISH). Deletions at 7q11 were found in 75% of the patients (22 out of 29). Nine deletions occurred on a paternal, and ten on a maternal chromosome; three deletions were demonstrated by FISH only, and parental origin could thus not be determined. All deletion patients aged between 2 years and puberty displayed a distinct pattern of facial features (including periorbital fullness, short nose with flat bridge, wide mouth, and full lips and cheeks), the characteristic outgoing social behaviour, as well as moderate growth and mental retardation. Two-thirds (15 out of 22) had a cardiovascular malformation, but only one third (7 of 22) had supravalvular aortic stenosis (SVAS). A stellate iris pattern was also present in one-third of the patients only. In the four adult patients with 7q11 deletions, there was prominence of the lower lip whereas fullness of cheeks and periorbital tissue was not seen.

CONCLUSION

This study confirms that WBS has a unique clinical picture which can be diagnosed clinically, but also shows that the relative frequency of individual features may have been overemphasized in the past, and that a minority of patients may exist who are clinically indistinguishable from WBS but who appear to have no deletion at 7q11.