We read with interest the article, published recently in this journal by Ronce et al. [1999] describing three generations of a French family segregating with a syndromal form of X-linked mental retardation (XLMR) characterized by hypotonia, intractable seizures, and severe mental deficiency. We wish to draw attention to four phenotypically similar families that were reported previously and described as an X-linked form of infantile spasms [Feinberg and Leahy, 1977;Rugtveit, 1986;Claes et al., 1997]. The affected males of these latter families [Ronce et al., 1999] presented with severe mental deficiency associated with early-onset intractable seizures typical of infantile spasms in most but not all cases.
We also have identified a large three-generation Canadian family with infantile spasms and mental retardation seen exclusively in male offspring from asymptomatic mothers, representing the fifth such family reported [Bruye `re et al., 1999]. Molecular studies using polymorphic microsatellite markers of chromosome X allowed us to determine the locus to be between marker DXS1226 and the adrenal hypoplasia locus in a 7-cM interval contained in the interval previously reported by Claes et al. [1997] and Ronce et al. [1999]. The marker DXS451, for which the two-point lod score with the XLMR gene was established to be 2.90 at a of 0.0, is contained between the two recombinations we de-scribed. Therefore, it is likely that the French family described by Ronce et al. [1999] represents a disorder allelic to, or perhaps even typical of, the disorder increasingly recognized as X-linked West syndrome.