LOCALIZATION OF THE GENE (OR GENES) FOR A SYNDROME WITH X-LINKED MENTAL-RETARDATION, ATAXIA, WEAKNESS, HEARING IMPAIRMENT, LOSS OF VISION AND A FATAL COURSE IN EARLY-CHILDHOOD

Linkage analysis is described in a family with X-linked mental retarda tion, ataxia, weakness, floppiness, delayed motor development, absence of deep tendon reflexes, hearing impairment and loss of vision (MIM n o. 301835). The disease has a fatal course due to the susceptibility o f the patients to infections, especially of the respiratory tract. Cli nical signs indicate impairment of the posterior columns, peripheral m otor and sensory neurons and the second and eighth cranial nerves and/ or their nuclei. The involvement of the posterior columns of the spina l cord is further suggested by the almost complete absence of myelinat ed fibers therein. We localized the responsible gene(s) to Xq21.33-q24 between DXS 1231 and DXS 1001 with a maximum lod score of 6.97. The p roteolipid protein gene, which codes for two myelin proteins of the ce ntral nervous system and is located in this region, was considered as a candidate gene for this disorder. However, no mutations were found i n the protein-coding part of this gene.