Marked phenotypic variable expression among brothers with duplication of Xq27.1 involving the SOX3 gene.

We describe four phenotypically different brothers who share the same microduplication of Xq27.1, which contains the SOX3 gene. SOX3 mutations have been associated with growth hormone deficiency, variable degrees of additional pituitary hormone deficiencies, and mental retardation. SOX3 also appears to play an important role in pharyngeal arch segmentation that gives rise to craniofacial structures. While these four brothers have inherited the same mutation, they manifest a spectrum of phenotypes, ranging from complete, multiple pituitary hormone deficiencies to no apparent pituitary hormone deficiency with or without craniopharyngeal/facial dysmorphisms. We look to the literature to provide putative explanations for the variable expression of the brothers' shared SOX3 mutation.