Bardet-Biedl syndrome (BBS) occurs with a prevalence of about 1:25,000. It is a ciliopathy in which retinitis pigmentosa, renal dysfunction and polydactyly are observed in combination with obesity, hypogonadism and behavioral abnormalities. The genetic causes are usually autosomal recessive, although triallelic inheritance has also been described. More than two mutations in more than one gene locus may be causative, so that a recessive inheritance of two variants in one gene may be accompanied by another variant in another BBS gene as a modifier of the clinical expression of the disease. More than 20 different BBS genes as well as other modifier genes have been described. In about 60-80% of clinically diagnosed cases, changes in the previously known BBS genes are detected, with the genes BBS1 and BBS10 being most frequently affected in Europeans (23% and 20% of cases, respectively).
Alström syndrome is a rare disease that shows phenotypic similarities to BBS and is caused by autosomal recessive genetic changes in the ALMS1 gene. The symptoms of Alström syndrome include retinitis pigmentosa, obesity, kidney and liver dysfunction, insulin resistance and hyperinsulinemia, and dilated cardiomyopathy.
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