Second case of Bardet-Biedl syndrome caused by biallelic variants in IFT74.

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive disorder of the cilia, often resulting in a phenotype of obesity, rod-cone dystrophy, a variable degree of intellectual disability, polydactyly, renal problems, and/or hypogonadism in males or genital abnormalities in females. We here report the case of an 11-year-old girl who presented with postaxial polydactyly, retinal dystrophy, and childhood obesity, suggesting Bardet-Biedl syndrome. She had no renal problems, developmental delay, or intellectual disability. Genetic testing revealed compound heterozygous variants in the IFT74 gene (c.371_372del p.Gln124Argfs*9 and c.16850-1G>T p.?). We here report the second patient with Bardet-Biedl syndrome due to biallelic IFT74 variants. Both patients have obesity, polydactyly, retinal dystrophy, and no renal abnormalities. The present case however, has normal intellect, whereas the other patient has intellectual disability. We hereby confirm IFT74 as a BBS gene and encourage diagnostic genetic testing laboratories to add IFT74 to their BBS gene panels.