Intellectual functioning in individuals with Bardet-Biedl syndrome

Objective: This study investigated intellectual functioning in individuals with Bardet-Biedl Syndrome (BBS). Method: 96 participants whose retrospective data from intellectual and adaptive skills assessments (Wechsler intelligence scales and Adaptive Behavior Assessment System [ABAS]) included in the Clinical Registry Investigating Bardet-Biedl Syndrome (CRIBBS) were analyzed. To obtain a more accurate estimate of intellectual function in the context of vision loss, participants with self-reported legal blindness at the time of assessment and those over the age of 15 were excluded from analyses of visual-spatial skills. Results: For participants for whom a Full-Scale IQ (FSIQ) could be obtained, mean FSIQ was 73.5, 38.3% had a FSIQ of 70 or less. Females had significantly higher FSIQ and visual intellectual skills compared to males. Nearly 60% of participants had verbal intellectual skills in the low average range and above (standard score 80+). Individuals with BBS1 had significantly stronger verbal intellectual skills compared to individuals with BBS10. However, composite adaptive functioning score did not differ between participants with BBS1 and BBS10. Conclusions: While intellectual functioning deficits are relatively common in individuals with BBS, there is a wide range of skill level. The absence of intellectual/cognitive impairment does not preclude a diagnosis of BBS. The lower FSIQ appears to be largely driven by non-verbal skills that rely on vision, which could be contributing to performances even in cases with less severe visual impairment. Individuals with BBS10 are more likely to have lower verbal intellectual functioning but general adaptive skills were equivalent between the two main BBS subtypes.