Mental retardation (MR) involves a complex collection of clinically and genetically diverse disorders. Diagnosis of MR is typically based on three main criteria: onset of symptoms before the age of 18, intellectual abilities significantly lower than average, and reduced adaptive skills. Individuals with MR tend to struggle in areas including communication, health, interpersonal/social skills, leisure, safety, self-guidance and care, school performance, and work.
 
X-linked mental retardation (XLMR) is associated with more than 200 conditions linked to >90 genes on the X chromosome. XLMR affects approximately 1/600-1/1000 males, as well as a significant number of females.   Mutations in these genes have been shown to be an underlying cause of mental retardation, which may or may not be associated with other congenital anomalies, developmental delay, autism, dysmorphism, and numerous genetic syndromes.  One of the XLMR-associated genes is PQBP1.

The polyglutamine binding protein 1 gene (PQBP1) encodes a putative transcriptional regulator that is expressed predominantly in the central nervous system during development. However, its specific biologic functions are yet to be determined. The PQBP1 gene is located at Xp11.23 and contains 7 exons. Missense mutations, small and gross deletions, as well as small insertions, have been reported in PQBP1. The major clinical features of patients with mutations in PQBP1 include mental retardation, microcephaly, and short stature (Cossée M et al. Eur J Hum Genet. 2006;14:418-425).