A novel variant of C12orf4 linked to autosomal recessive intellectual disability type 66 with phenotype expansion

Background: Intellectual disability (ID) is a hallmark of many rare disorders that are highly heterogeneous and complex. A large number of specific genes are involved in development of this heterogeneity, and each of these genes is only found in a small number of patients. This weakens the definition of the predominant genotype and the phenotypic characteristics associated with that gene. Autosomal recessive ID type 66 (OMIM #618221) is one of these very rare diseases created by defects in the C12orf4 gene.

Methods: The present study included two patients from an Iranian family with initial diagnosis of non-syndromic ID, aiming to identify the possible genetic cause(s), and whole-exome sequencing (WES) was performed for the proband. The obtained variant was confirmed by Sanger sequencing and co-segregated in the family.

Results: The patients carried a novel pathogenic splicing variant called c.1441-1G>A in exon 12 of the C12orf4 gene (NM_001304811). They predominantly manifested ID, behavioral problems, speech impairment and dysmorphic facial features, some of which had not been reported in previous studies.

Conclusions: A novel pathogenic splicing variant was identified named c.1441-1G>A in the C12orf4 gene. To date, only seven families have been reported with defects in this gene. Previous studies have not highlighted the exact clinical manifestations of these patients; thus, the present study could contribute to a better delineation of the genotype-phenotype correlation and interpretation of very rare variants of the gene.