X-linked Dominant Inheritance Pattern Research Articles

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.

Familial congenital periodic alternating nystagmus with presumably X-linked dominant inheritance

Familial congenital periodic alternating nystagmus (PAN) with presumably X-linked dominant inheritance (XLPAN) was observed in the proband and her mother. Many relatives had nystagmus by history. A pedigree was constructed with the data provided by the mother. Permission could not be obtained to contact any other relatives, but incidental medical data were obtained from elsewhere. From the pedigree it appeared that an X-linked dominant pattern of inheritance was most probable. The proband experienced symptomatic relief of oscillopsia by baclofen therapy (final dose 90 mg/day) but there was no appreciable change in the nystagmus intensity (at 120 mg/day).