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

Area of Science:

• Genetics
• Molecular Biology
• Clinical Diagnostics

Background:

• Martin-Probst syndrome (MPS) is an X-linked disorder characterized by deafness and intellectual disability.
• The RAB40AL gene was previously suggested as the locus for MPS based on limited family segregation and in vitro studies of a specific missense variant (p.D59G).

Purpose of the Study:

• To investigate the role of the RAB40AL gene, specifically the p.D59G variant, in the etiology of Martin-Probst syndrome.
• To assess the prevalence of the p.D59G variant in a general population to determine if it represents a disease-causing mutation or a common polymorphism.

Main Methods:

• Whole-exome sequencing was performed on two patients with suspected MPS.
• The p.D59G variant was screened in 810 DNA samples from a general Polish population using allele-specific PCR and direct DNA sequencing for verification.

Main Results:

• The p.D59G variant was identified in two patients, but MPS was excluded in both cases.
• Screening revealed the p.D59G variant in 2.47% of the general Polish population (8/405 males, 12/405 females), indicating high prevalence.
• The observed frequency of the p.D59G variant is consistent with a common genetic variation in asymptomatic individuals.

Conclusions:

• The findings challenge the role of RAB40AL mutations, particularly the p.D59G variant, as the cause of Martin-Probst syndrome.
• The high prevalence of the p.D59G variant in the general population suggests it is not pathogenic for MPS.
• This study has significant diagnostic implications given the increasing use of next-generation sequencing in clinical practice.