A Novel Homozygous Variant in Gene in a Patient with Developmental Deficits.

Background: Oral-facial-digital syndrome (OFDS) type 6 is a rare subtype of Joubert syndrome characterized by orofacial anomalies and polydactyly with neurological features of Joubert syndrome. This rare syndrome is divided into thirteen subtypes, all of which demonstrate autosomal recessive inheritance, except for OFDS type 1 which demonstrates X-linked dominant inheritance.

Case Presentation: A 19-year-old man with mild developmental delay was brought to a rural community clinic, as he had become irritable and angry, in the recent past. There was no history of prior medical conditions. In view of orofacial anomalies, and developmental deficits, a genetic analysis was requested. Karyotype analysis revealed a normal male karyotype (46,XY) in all 30 metaphase spreads analyzed. No numerical or structural chromosomal abnormalities were observed. Clinical exome sequencing and chromosomal microarray detected a variant of uncertain significance in exon 5 of gene c.365T>G (p.Val122Gly) leading to substitution of Glycine for Valine. This was confirmed by Sanger sequencing. Parents were heterozygous, and the unaffected sibling was homozygous for the wild-type allele. This variant has not been reported earlier in the mutation databases or gnomAD. Runs of homozygosity (ROH) analysis showed a 3.2 Mb ROH around the gene in the proband, which was absent in both parents and the unaffected sibling.

Conclusion: We find a novel homozygous mutation in the gene in a patient of non-consanguineous parentage with atypical orofacial features. This suggests that potentially deleterious, rare variants may occur in the heterozygous state in the population. Hence, sequencing of population samples might help understand the genetic epidemiology of rare syndromes.