FRAXE-associated intellectual disability: clinical and molecular insights into an underdiagnosed condition

Abstract

FRAXE-associated intellectual developmental disorder (FRAXE-ID) is a rare X-linked condition resulting from disruption of the AFF2 gene, usually through expansion of more than 200 CCG repeats and subsequent hypermethylation. Despite an estimated incidence of 1 in 50,000 to 100,000 males, it remains underdiagnosed due to its variable and non-specific phenotype. This report presents the clinical and molecular findings of three unrelated young male patients diagnosed with FRAXE-ID. All exhibited global developmental delay, mild to moderate intellectual disability, and subtle dysmorphic features. Molecular testing confirmed full mutations in the AFF2 gene in all cases, with one patient demonstrating size mosaicism. Southern blot confirmed hypermethylation of expanded alleles. The mothers of all three patients were premutation carriers. These findings emphasize the non-syndromic and often overlooked nature of FRAXE-ID. Accurate diagnosis relies on specific molecular techniques, underscoring the importance of clinical awareness and targeted testing to ensure appropriate diagnosis, management, and genetic counselling.