The phenotype in Norwegian patients with Bardet-Biedl syndrome with mutations in the BBS4 gene.

Objective: To describe the phenotype of the Bardet-Biedl syndrome in patients with mutations in the BBS4 gene.

Methods: We examined 3 pairs of siblings with Bardet-Biedl syndrome in whom 3 different mutations in the BBS4 gene were detected, 2 of which were homozygous for the mutation.

Results: All patients had an increased body mass index. The obesity varied between families from moderate to severe. All of the males had hypogenitalism. All had brachydactyly and similar dental anomalies. Polydactyly was present in 5 of the 6 patients. The number and location of the extra digits varied even between siblings. The intelligence varied between families and was within the normal range in 4 individuals. One male had spinal stenosis with paraparesis of his legs. Four patients had increased blood pressure, but only 1 had impaired renal function. Severe retinitis pigmentosa with onset in early childhood was present in all patients. There were few abnormal retinal pigmentary deposits even at advanced stages.

Conclusions: The phenotype of patients with BBS4 mutations consists of severe retinitis pigmentosa, variable obesity, brachydactyly with variable polydactyly, small or missing teeth, genital hypoplasia, and cardiovascular disease. The combinations of clinical signs are mostly independent of the individual BBS4 mutation and can vary even within pairs of siblings. It is possible that there is a characteristic appearance of the ocular fundus in patients with BBS4 mutations.