In this issue of the Journal, Rio et all describe a new syndromic form of X-linked mental retardation (XLMR). The phenotype seems to be quite distinct, characterized by mild mental delay, peculiar facial traits, short stature and hypergonado-trophic hypogonadism. It is caused by a small Xq27.3-Xq28 duplication of 5.1 Mb, encompassing 28 genes, including FMR1 but not MECP2. Obligate carrier mothers were of normal intelligence, but presented with short stature and early menopause. One of them had a completely skewed inactivation of . the duplicated X chromosome. Altogether, three out of five carriers had a completely skewed X inactivation. This new condition represents an important addition to the still-growing list of XLMR syndromes.
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