First report of Klein-Waardenburg Syndrome in Iran and a novel pathogenic splice site variant in PAX3 gene.

Objectives: Waardenburg Syndrome (WS) as a congenital auditory-pigmentary syndrome is a clinically and genetically heterogeneous disorder. Based upon clinical manifestations, it can be classified into four types. Loss of function mutations in PAX3 gene cause WS1 and WS3 (Klein-Waardenburg syndrome). While WS2 and WS4 have locus heterogeneity with multiple causative genes. Here we report a novel splice site variant in a pedigree with multiple affected members. Based on diagnostic criteria, three of them are associated with WS3. The remained patients classified as type 1.

Methods: PCR amplification and Sanger sequencing were performed for all exons and all exon-intron boundaries of PAX3 (NM_181,459) gene of the proband. Then available symptomatic and asymptomatic members were screened for the detected variant. Interpretation and classification of the variant were done based on the current guidelines.

Results: We identified a novel heterozygous splice site variant (c.586+2T > C) in donor site of intron 4 of PAX3 gene in our proband. Moreover, this variant was co-segregated with the disease in other available five affected members. Also, the detected variant was not detected in any of the investigated asymptomatic members. This variant was classified as a pathogenic variant.

Conclusions: This study shows significant intra-familial clinical heterogeneity and absence of phenotype-genotype correlation in a pedigree with Waardenburg Syndrome. However, severity of phenotypes and additional symptoms in the patients can be related to alternative splicing and different levels of PAX3 gene expression. Detailed evaluation of more cases can shed light on this and case-reports are valuable traffic sign in the road. This article is the first report of Waardenburg syndrome type 3 in Iran.