Alport's syndrome

The use of genetic testing in the evaluation of hearing impairment in a child

PURPOSE OF REVIEW

To review the role of genetic testing in the evaluation of hearing impairment in children.

RECENT FINDINGS

The introduction of genetic testing has greatly enhanced the evaluation of deafness and hearing impairment in children. It can save time and money as well as providing patients, their families, and their physicians with important information; however, this testing is different from the medical testing that pediatricians typically order.

SUMMARY

For patients and families to realize the benefits of genetic testing it must be done early in the evaluation process and must be accompanied by appropriate pretest and posttest counseling.

Exclusion of epidermal growth factor and high-resolution physical mapping across the Rieger syndrome locus

We have evaluated the 4q25-4q26 region where the autosomal dominant disorder Rieger syndrome has been previously mapped by linkage. We first excluded epidermal growth factor as a candidate gene by carrying out SSCP analysis of each of its 24 exons using a panel of seven unrelated individuals with Rieger syndrome. No evidence for etiologic mutations was detected in these individuals, although four polymorphic variants were identified, including three that resulted in amino acid changes. We next made use of two apparently balanced translocations, one familial and one sporadic, to identify a narrow physical localization likely to contain the gene or to be involved in regulation of gene function. Somatic cell hybrids were established from individuals with these balanced translocations, and these hybrids were used as a physical mapping resource for, first, preliminary mapping of the translocation breakpoints using known sequence tagged sites from chromosome 4 and then, after creating YAC and cosmids contigs encompassing the region, for fine mapping of those breakpoints. A cosmid contig spanning these breakpoints was identified and localized the gene to within approximately 150 kb of D4S193 on chromosome 4. The interval between the two independent translocations is approximately 50 kb in length and provides a powerful resource for gene identification.

Alport's syndrome in 78 patients: epidemiological and clinical study

In a nationwide study in Finland, 78 patients, 38 male and 40 female in 25 families, were found to have Alport's syndrome, corresponding to 1 in 53,000 live births. This frequency of clinically manifest Alport's syndrome was much lower than expected from earlier reports. This first sign of the disease was most often haematuria, but was sometimes proteinuria or hearing loss. These signs were detected at a similar median age in both boys and girls, namely 6.2 and 6.0 years, respectively. The patients were followed up over a median period of 12.1 years (range 0.1 - 34.0 years). The clinical course of the disease was more severe in the male subjects than in the female subjects: 53% of the males and 13% of the females developed terminal renal failure at median ages of 24.9 and 31.1 years, respectively. At the last observation, 34% males and 78% females were free of renal insufficiency at median ages of 10.3 and 26.8 years. Hearing loss was detected in 74% of the males and 5% of the females. Regarding the rate of deterioration of renal function, no statistically significant difference was noticed between males and females. The routine use of dialysis and transplantations has dramatically changed the life expectancy of the patients.