Sequence variants in different genes underlying Bardet-Biedl syndrome in four consanguineous families

BACKGROUND

Bardet-Biedl Syndrome (BBS) is a rare (1:13,500-1-160,000) heterogeneous congenital disorder, characterized by postaxial polydactyly, obesity, hypogonadism, rod-cone dystrophy, cognitive impairment, and renal abnormalities (renal cystic dysplasia, anatomical malformation). To date about twenty-five genes have been identified to cause BBS, which accounts for about 80% of BBS diagnosis.

METHODS

In the current study, we have performed mutational screening of four Pakistani consanguineous families (A-D) with clinical manifestation of BBS by microsatellite-based genotyping and whole exome sequencing.

RESULTS

Analysis of the data revealed four variants, including a novel/unique inheritance pattern of compound heterozygous variants, p.(Ser40*) and p.(Thr259Leufs*21), in MKKS gene, novel homozygous variant, p.(Gly251Val)] in BBS7 gene and two previously reported p.(Thr259Leufs*21) in MKKS and p.(Met1Lys) in BBS5 gene. The variants were found segregated with the disorder within the families.

CONCLUSION

The study not only expanded mutations spectrum in the BBS genes, but this will facilitate diagnosis and genetic counselling of families carrying BBS related phenotypes in Pakistani population.

Novel Mutations in the MKKS, BBS7, and ALMS1 Genes in Iranian Children with Clinically Suspected Bardet–Biedl Syndrome

Bardet–Biedl syndrome is a rare autosomal recessive form of syndromic obesity which is characterized by retinal degeneration, obesity, polydactyly, cognitive impairment, and renal and urogenital anomalies. In this study, we used whole-exome sequencing (WES) to investigate the underlying mutations in four Iranian children from consanguineous families with a clinical diagnosis of Bardet–Biedl syndrome (BBS). In three out of four children, we identified one previously reported frameshifting variant in the BBS12 gene (c.265-266delTT, p.L89fs) and two novel nonsense variants in MKKS (c.1196T>G, p.L399X) and BBS7 genes (c.1636C>T, p.Q546X). In the other child, no mutations were detected in known genes for BBS. However, we identified a novel variant in the ALMS1 gene (c.10996delC, p.Q3666fs) indicative of Alström syndrome. All variants were interpreted as pathogenic according to American College of Medical Genetics and Genomics (ACMG) guidelines and confirmed through Sanger sequencing. In conclusion, our results not only expand the spectrum of mutations in BBS and ALMS1 genes but also accentuate the importance of genetic testing for differentiating BBS from Alström syndrome.