Evidence against RAB40AL being the locus for Martin-Probst X-linked deafness-intellectual disability syndrome.

RAB40AL has been reported as the locus for Martin-Probst syndrome (MPS), an X-linked deafness-intellectual disability syndrome. The report was based on segregation of a missense change p.D59G with the disease in a single family and in vitro localization studies. We found the p.D59G variant by whole-exome sequencing in two patients; however, the diagnosis of MPS was excluded in both cases. Furthermore, screening of control DNA samples (n = 810) from a general Polish population, using allele-specific PCR and direct DNA sequencing for verification, identified p.D59G in 8/405 males and 12/405 females. High prevalence of the p.D59G variant (2.47%) is typical for a common genetic variation observed in asymptomatic individuals. Our data question the role of RAB40AL mutation as a disease-causing change and the involvement of RAB40AL in MPS. Considering an increasing use of next-generation sequencing in the clinical setting, our finding is of practical diagnostic importance.