In contrast to the preponderance of affected males in families with X-linked mental retardation, Rett syndrome (RTT) is a neurological disorder occurring almost exclusively in females. The near complete absence of affected males in RTT families has been explained by the lethal effect of an X-linked gene mutation in hemizygous affected males. We report here on a novel mutation (A140V) in the MECP2 gene detected in one female with mild mental retardation. In a family study, the A140V mutation was found to segregate in the affected daughter and in four adult sons with severe mental retardation. These results indicate that MECP2 mutations are not necessarily lethal in males and that they can be causative of non-specific X-linked mental retardation. ß

weight, and apparatus dead volume for a solute on a given liquid phase. It is assumed that the isothermal temperature dependence of the retention index is negligible over a range of retention temperatures which might be obtained for different programs. This assumption is valid for the vast majority of solutes, as shown by the data of Kovats (8) and Wehrli and Kovats (IS), who introduced the use of the retention index for isothermal gas chromatography.Retention indices were obtained for some esters, alcohols, aldehydes, and ketones on each of the two columns used under the conditions of this study.

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