Identification of a novel truncating variant in AHI1 gene and a brief review on mutations spectrum.

Joubert syndrome (JS) is a rare inherited neurodevelopmental condition characterized by hypotonia, ataxia, developmental delay, abnormal eye movements, neonatal respiratory disturbance and unique midbrain-hindbrain malformation, known as the molar tooth sign. JS is a genetically heterogeneous disorder with nearly 35 ciliary genes are implicated in its pathogenesis. AHI1 gene is one of the most frequently mutated gene in JS patients which is accounted for 8-11% of cases, particularly in Arab population. AHI1 encodes a cilium-localized protein with a significant role in mediating vesicle trafficking, ciliogenesis and cell polarity. Here, we report a novel pathogenic variant in AHI1 gene and review previously published mutations in AHI1 gene briefly. Whole exome sequencing was employed to determine the causative mutation in an Iranian Arab family with JS from southwestern Iran. Segregation analysis of the candidate variant in the family members was performed using PCR-Sanger sequencing. This approach found a novel homozygous nonsense variant c.832C > T (p.Gln278Ter) in AHI1. Segregation analysis was consistent with individual's phenotype and an autosomal recessive pattern in the family. The variant residing in a relatively highly conserved region and fulfilled the criteria required to be classified as a pathogenic variant based on American College of Medical Genetics and Genomics guidelines. This study confirms the diagnosis of JS in this family and highlights the efficiency of next-generation sequencing-based technique to identify the genetic causes of hereditary disorders with locus heterogeneity.