X-linked incomplete achromatopsia with more than one class of functional cones

Five affected males in the fifth generation of a large pedigree of X-chromosomal incomplete achromatopsia were tested. All had SWS cone function. A 19-year-old affected man was a classical blue cone monochromat on color matching and spectral sensitivity. A 16-year-old boy showed evidence of a long wavelength sensitive cone active in 8 degrees color matches. With a blue-green background, his cone spectral sensitivity function peaked near 550-560 nm. Three younger boys, aged 7-10 yrs were evaluated only with color matching. All showed evidence of long wavelength cone function with an 8 degree field and one showed long wavelength cones in 2 degree matches. An independent observation concerning the family was the finding that deuteranomaly was introduced in the third generation. The fourth generation women, all obligate carriers of X-linked achromatopsia, had a 0.5 chance to carry deuteranomaly. Neither carrier state per se is usually associated with expression of deuteranomaly. Three of the five tested expressed deuteranomaly. This finding of deuteranomaly in the carrier females might be a consequence of a double carrier state indicating association between the genes for deuteranomaly and X-linked achromatopsia

Relationship between trinucleotide repeat expansion and phenotypic variation in Huntington's disease

The molecular analysis of a specific CAG repeat sequence in the Huntington's disease gene in 440 Huntington's disease patients and 360 normal controls reveals a range of 30−70 repeats in affected individuals and 9−34 in normals. We find significant negative correlations between the number of repeats on the HD chromosome and age at onset, regardless of sex of the transmitting parent, and between the number of repeats on the normal paternal allele and age at onset in individuals with maternally transmitted disease. This effect of the normal paternal allele may account for the weaker age at onset correlation between affected sib pairs with disease of maternal as opposed to paternal origin and suggests that normal gene function varies because of the size of the repeat in the normal range and a sex−specific modifying effect