Certain germline mutations in either BRCA1 or BRCA2 confer a lifetime risk of developing breast cancer that may approach 90%. The BRCA1 185delAG mutation was found in 20% and the BRCA2 6174delT mutation in 8% of Ashkenazi Jewish women with early-onset breast cancer. The 185delAG mutation was observed in 0.9% of 858 Ashkenazi Jews unselected for a personal or family history of cancer. Assuming comparable age-specific penetrances, a carrier frequency of 0.3% was estimated for the 6174delT BRCA2 mutation. To test this hypothesis, we performed a population survey of 1,255 Jewish individuals. In two independent groups, a prevalence of approximately 1% (C.I. 0.6-1.5) was observed for the 6174delT mutation. The relative risk of developing breast cancer by age 42 was estimated to be 9.3 (C.I. 2.5-22.5) for 6174delT, compared to 31 (C.I. 11-77) for 185delAG. Analysis of 107 Ashkenazi Jewish women with breast cancer and a family history of breast or ovarian cancer confirmed a four-fold greater prevalence for the BRCA1 185delAG mutation compared to the BRCA2 6174delT mutation. Our findings suggest a difference in cumulative life-time penetrance for the two mutations. Genetic counseling for the one in 50 Ashkenazi Jewish individuals harbouring specific germline mutations in BRCA1 or BRCA2 must be tailored to reflect the different risks associated with the two mutations.

A retrospective study was undertaken to answer the following questions: Is the sensorineural hearing loss (SNHL) in Turner syndrome progressive? Can the occurrence of hearing loss be explained by the parental origin of the intact X chromosome? Twenty-four individuals recruited through the Turner Syndrome Society completed a questionnaire and submitted sufficient medical records to determine their otologic status. The majority (21/24) have had problematic otitis media (OM), and two thirds (16/24) have SNHL. In seven of the Turner subjects (age range: 12 to 51 years), gradual progressive SNHL began in late childhood or early adulthood. Molecular techniques showed no correlation between parental origin of the retained X chromosome and hearing status in 17 Turner subjects and at least one of their parents. SNHL and frequent OM appear to be independent variables that are both present in Turner syndrome. It is postulated that the presence of unpaired genes on the X chromosome may account for hearing loss and other phenotypic abnormalities seen in this syndrome.

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