An emerging phenotype of Xq22 microdeletions in females with severe intellectual disability, hypotonia and behavioral abnormalities.

The majority of Xq22 duplications seen in patients with Pelizaeus-Merzbacher disease (PMD) include proteolipid protein 1 (PLP1), the gene responsible for PMD, and neighboring genes. Some cases result from larger duplications up to 7 Mb in size. In comparison, the deletions including PLP1 seen in PMD patients are small. In this study, we present the genetic and clinical information for five female patients with deletions involving the Xq22 region, and review the correlation between the genotype and phenotype. Three of the five patients show similar large deletions (>3 Mb) ranging from Xq22.1 to Xq22.3 and all manifest severe intellectual disability, hypotonia and behavioral abnormalities. The most striking similarity among them are the behavioral problems, including poor eye contact and sleep disturbance. We propose that this represents an emerging distinctive microdeletion syndrome encompassing PLP1 in female patients. The possible candidate region responsible for such distinctive features has been narrowed down to the neighboring region for PLP1, including the interleukin 1 receptor accessory protein-like 2 (IL1RAPL2) gene and the clustered brain expressed X-linked (BEX) genes. The gene(s) responsible for severe neurological features in the patients in this study would be located in the regions proximate to PLP1; thus, males with the deletions involving the gene(s) would be lethal, and finally, the sizes of the deletions in PMD patients would be smaller than those of the duplications.