Clinical and genetic aspects of Bardet-Biedl syndrome in adults in Norway.

Abstract

Background: Bardet-Biedl syndrome (BBS) is a rare nonmotile ciliopathy characterized by retinal dystrophy, polydactyly, obesity, genital anomalies, renal dysfunction, and learning difficulties. The objectives were to describe the retinal, oral, and metabolic characteristics relevant to adults with BBS as well as the prevalence of genetic variants.

Methods: A cross-sectional study of 30 adults with BBS (15 males, 15 females, mean age 39.8 ± 13.6 years) was recruited from a single centre for rare disorders in Norway. Participants attended a one day hospital visit including medical (blood pressure, body mass index), ophthalmological and oral examinations. Blood samples were collected and genetic analyses were performed.

Results: Age at diagnosis varied from one year to 30 years. The incidence of overweight/obesity, hypertension, kidney disease, and diabetes mellitus was 82%, 67%, 27%, and 23%, respectively. All had retinitis pigmentosa. Prior to the study, 14 participants (47%) had confirmed extinguished electroretinography. Eleven participants were examined with electroretinography during the study period, and all had extinguished electroretinography. 50% perceived light, 23% saw hand motion, and one participant did not perceive light. Oral anomalies were identified in 77% of the participants, including abnormal palates (58%), crowded teeth (50%), and small teeth (60%). A genetic cause was identified in all participants, most commonly in BBS1 (n = 11) and BBS10 (n = 9). Other variants were found in BBS5, BBS7, BBS9, and MKKS. In addition to exon-located variants, a novel deep intronic variant causing mis-splicing was identified in BBS7.

Conclusions: A multidisciplinary examination is important for proper management of BBS. The genotype and phenotype of this sample were heterogeneous, including kidney failure, genital anomalies and obesity. Genome sequencing increased the likelihood of identifying the genetic cause. In BBS populations, the patients will benefit from testing or reanalysis, preferably with genome sequencing, including searching for deep intronic variants.