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Mutations in genes on the X chromosome are believed to be responsible for the excess of males among individuals with mental retardation. Such genes are numerous, certainly >100, and cause both syndromal and nonsyndromal types of mental retardation. Clinical and molecular studies have been conducted on the Mennonite family with X-linked mental retardation (XLMR) reported, in 1962, by Renpenning et al. The clinical phenotype includes severe mental retardation, microcephaly, up-slanting palpebral fissures, small testes, and stature shorter than that of nonaffected males. Major malformations, neuromuscular abnormalities, and behavioral disturbances were not seen. Longevity is not impaired. Carrier females do not show heterozygote manifestations. The syndrome maps to Xp11.2-p11.4, with a maximum LOD score of 3.21 (recombination fraction 0) for markers between DXS1039 and DXS1068. Renpenning syndrome (also known as "MRXS8"; gene RENS1, MIM 309500) shares phenotypic manifestations with several other XLMR syndromes, notably the Sutherland-Haan syndrome. In none of these entities has the responsible gene been isolated; hence, the possibility that two or more of them may be allelic cannot be excluded at present.

Ten patients displaying a uniform Cerebro‐Oculo‐Facio‐Skeletal (COFS) syndrome are presented. The syndrome is characterized by microcephaly, hypotonia, microphthalmia, cataracts, blepharophimosis, large ear pinnae, prominent root of the nose, micrognathia, widely set nipples, camptodactyly, flexure contractures at the elbows and knees, generalized osteoporosis, dysplastic acetabula, coxa valga and vertical talus manifesting as rocker bottom feet. Marked failure to thrive and repeated lower respiratory infections led to death within the first three years of life. Evidence strongly suggestive of autosomal recessive inheritance is presented.