BBS cognitive study shows wide range of intellectual abilities across ages
Findings may help guide school supports and accommodations
Written by |
A study of people with BBS found a wide range of intellectual abilities, with some test scores potentially affected by vision-related demands (Photo by iStock)
People with Bardet-Biedl syndrome (BBS) show a wide range of cognitive skills, but verbal skills do not seem to represent a particular weakness compared with other intellectual skills, according to a study based on standard intelligence quotient (IQ) tests.
Lower scores on nonverbal tasks may be partly explained by the fact that these IQ test tasks often rely on vision, which is commonly impaired in people with BBS, the researchers noted.
In addition, people with BBS due to mutations in the BBS10 gene had lower verbal skill scores than those carrying mutations in the BBS1 gene.
BBS study may help guide school supports
“The findings can serve as a tentative guide or a starting point for educators during development of educational interventions and accommodations,” the researchers wrote. “For example, findings would suggest that children with BBS may benefit from extra time to complete tasks, particularly those that involve visual stimuli.”
The study, “Intellectual functioning in individuals with Bardet–Biedl syndrome,” was published in The Clinical Neuropsychologist.
BBS affects many parts of the body, causing a wide range of symptoms that vary from person to person. In addition to obesity, BBS often causes gradual loss of vision. Some patients may also experience learning challenges or cognitive impairment.
To understand how BBS affects cognitive skills, the researchers analyzed retrospective assessment data from 96 patients, ages 4 to 49, in the Clinical Registry Investigating Bardet-Biedl Syndrome (CRIBBS), an ongoing patient registry (NCT02329210). Most patients were female (58.3%).
The largest proportions of patients carried mutations in the BBS1 gene (35.4%) and the BBS10 gene (33.3%), two of the most common BBS-associated genes.
The records included the Wechsler Intelligence scales and the Adaptive Behavior Assessment System, a measure of daily living and social skills. For analyses involving tests with significant visual demands, the researchers limited the group to patients ages 4 to 15 and excluded younger patients with self-reported legal blindness. Some of these tests assess visual-spatial skills, which are needed to perceive and process visual information and spatial relationships, such as telling where objects are in space.
Among the 54 patients in the subgroup analyzed for visually demanding tasks, 47 had available full-scale IQ scores. Their mean score was 73.5, which is below average. In the general population, the average score is 100. Eighteen of those 47 patients (38.3%) scored below 70, which is often used as a guideline when considering intellectual disability.
IQ scores varied widely across participants
However, full-scale IQ scores ranged widely, from as low as 40 to 108, and girls in the visually demanding task subgroup scored higher than boys, with mean scores of 78 vs. 68. Some patients had scores within or above the average range, the team noted, adding that testing within average should not rule out a diagnosis of BBS.
Many tasks in intelligence testing depend on seeing patterns, shapes, or visual details. Because BBS often causes vision loss, it may lower some test scores even when cognitive skills are stronger than they appear.
For this reason, the researchers looked separately at language skills using the Verbal Comprehension Index (VCI), which measures language understanding, reasoning, and verbal knowledge.
The average VCI score was 83.5, which falls in the low average range. As with the full-scale IQ, language skills varied widely, with VCI ranging from 45 to 127. “In 37% of participants, verbal intellectual skills were in the average range and above (90 [plus]),” the researchers wrote.
On average, patients with BBS1 mutations had higher verbal skill scores than those with BBS10 mutations (VCI 86.8 vs. 79.4).
The researchers looked at working memory using the Working Memory Index (WMI). Working memory refers to the ability to hold and use information in the mind for short periods, such as remembering instructions or doing mental calculations. The average WMI score was 80.4, at the low end of the low average range, although scores ranged from severely impaired to above average.
Visual-spatial skills were measured with the Visual Spatial Index, and the average score was 78.3, which is below average. Processing speed, measured by the Processing Speed Index (PSI), was also below average, with an average score of 73.5. Processing speed reflects how quickly a person can complete simple mental tasks accurately.
Verbal skills were not a main weakness
“While previous research has identified that early language skills appear to be the most common developmental delay in children with BBS, verbal intellectual skills … do not appear to represent a particular weakness for people with BBS compared to other intellectual skills,” the researchers wrote.
The researchers also looked at adaptive skills, which include daily tasks and social skills. These were measured using the General Adaptive Composite (GAC) score. Better cognitive skills were linked to better adaptive functioning overall. Although patients with BBS10 mutations tended to have lower cognitive scores, adaptive functioning in this subset did not significantly differ between the BBS1 and BBS10 groups.
“The results suggest that some aspects of intellectual functioning are weaker for individuals with BBS10 compared to BBS1,” the team wrote.
“Increased knowledge regarding characteristics of individuals with BBS will result in improved clinical care, such as more accurate and earlier diagnosis, prognosis, access to early intervention services, academic and employment opportunities, and support services in daily life,” the researchers wrote.
They noted that “there is a substantial number of individuals with BBS who have average and above average intellectual skills and their opportunities should not be artificially limited by inaccurate estimates of cognitive function or a presumption of cognitive dysfunction.”