Developmental delays are a widely recognized feature of Bardet-Biedl syndrome (BBS); however, there is little research on the challenges faced by people with BBS.
People with Bardet-Biedl syndrome (BBS) appear to encounter delays in acquiring adaptive skills and expressive language, Ekaterina Keifer, PhD, and colleagues report in a study published in American Journal of Medical Genetics.
“Results revealed wide-ranging delays in adaptive skills, particularly in the domain of Self-Care,” Dr. Keifer and colleagues wrote. “With regard to developmental milestones, expressive language delays were found most frequently in children with BBS compared to motor and social/communication milestones.”
A Rare Disease With Wide-Ranging Developmental Challenges
BBS is an autosomal recessive disorder that affects multiple body systems. Researchers estimate BBS to be around 1:100,000 in North America and Europe. The features of this rare ciliopathy include retinal degeneration resulting in progressive visual impairment, abnormal electroretinogram, nystagmus, hearing impairment, polydactyly, syndactyly, obesity, short stature, renal and genital abnormalities, hypertension, skeletal muscle atrophy, and developmental and cognitive delays. Symptoms can begin at any age.
Of the 27 BBS genes that have been identified, most cases involve BBS1 or BBS10. Cilia dysfunction appears to affect brain development, but the mechanisms involved are not fully understood.
Developmental Delays Are Prominent
Developmental delays are widely recognized as a feature of BBS, but little is known about the challenges faced by people with BBS.
The authors had two goals in, to their knowledge, the first study to specifically examine early development up to the age of 6: 1.) to investigate the achievement of ten developmental milestones in children with BBS, and 2.) to investigate adaptive functioning in children with BBS.
To assess the achievement of the developmental milestones, the researchers analyzed data from retrospective responses of 652 people with BBS who were enrolled in the ongoing Clinical Registry Investigating Bardet-Biedl syndrome (CRIBBS). At the time they or their caregivers were surveyed annually by phone with yes-or-no questions about developmental milestones, participants ranged in age from 3 months to 68 years age and averaged 15.9 years.
“When we compared developmental milestones in subsets of participants divided by BBS genotype (BBS1 and BBS10), a lower percentage of participants with BBS10 was rated to achieve independent head holding by 4 months [P=0.031], unsupported walking by 18 months [P= 0.070], self-feeding with a spoon by 18 months [P= 0.024], and running by 2 [P=0.011]. There was no significant difference between the two genotypes on speech milestones,” Keifer and colleagues explain.
To assess early adaptive skills, the study team surveyed the caregivers of 101 children aged between 0 and 5 years who had available data in the Adaptive Behavior Assessment System (ABAS-II 0–5) Of these, 95 children were also in the CRIBBS registry. Among the areas assessed annually by the ABAS-II questionnaire were Communication (e.g., “looks at others’ faces when they are talking”), Functional Pre-Academics (e.g., “points to pictures in books when asked, for example, points to a horse or a cow”), and Self-Care (e.g., “swallows liquids with no difficulty”).
The researchers found a wide range of delays in adaptive skills, especially regarding self-care. Expressive language appeared to be the most frequently delayed developmental milestone. Children with the BBS10 gene tended to have lower early developmental and adaptive skills when compared with those with the BBS1 gene; and as they aged, their adaptive skills scores tended to lag farther behind (Table).
“Knowing which clinical conditions are more likely to be linked with certain genotypes could help clarify prognosis, direct more careful personalized care, and provide targeted intervention,” the authors note.
Keifer and colleagues acknowledge that limitations to the study include its retrospective design that relied on recall of past developmental milestones; selection bias; and confounding variables such as age at diagnosis, enrollment in the registry, and access to interventions and resources; and BBS genetic subtype.
This research “highlights the importance of early and baseline assessment of developmental, adaptive, and behavioral features using standardized assessment methods in all children diagnosed with BBS,” they conclude. “This would help track developmental trajectories in a more consistent and systematic manner, allowing for targeted intervention and evaluation of progress/improvement in both clinical and research settings.”
