Evolution of ocular clinical and electrophysiological findings in pediatric Bardet-Biedl syndrome

Retinitis pigmentosa in Laurence-Moon-Bardet-Biedl syndrome in India: Electronic medical records driven big data analytics: Report II

Purpose:

To describe the clinical presentation and demographic distribution of retinitis pigmentosa (RP) in Laurence–Moon–Bardet–Biedl (LMBB) syndrome patients.

Methods:

This is a cross-sectional observational hospital-based study wherein 244 patients with RP in LMBB syndrome presenting to our hospital network between March 2012 and October 2020 were included. An electronic medical record database was used for data retrieval.

Results:

There were 244 patients in total, with a hospital-based prevalence rate of 0.010% or 1000/100,000 population. The mean and median age of patients was 15.22 ± 7.56 and 14 (IQR: 10–18.5) years, respectively, with the majority being in the age group of 11–20 years (133/244 patients; 54.50%). Males were more commonly affected (164 patients; 67.21%), and the majority (182 patients; 74.59%) were students. All 244 patients (100%) complained of defective central vision at presentation. More than one-fourth of the patients had severe visual impairment to blindness at presentation. Prominent retinal feature at presentation was diffuse or widespread retinal pigment epithelial degeneration in all patients.

Conclusion:

Patients with RP in LMBB syndrome present mainly in the first to second decade of life with severe visual acuity impairment to blindness early in life. It is important to rule out LMBB syndrome in early-onset RP with central visual acuity impairment. On the contrary, all patients diagnosed or suspected with LMBB syndrome systemic features at physician clinic should also be referred for ophthalmic evaluation, low vision assessment, rehabilitation, and vice versa.

Characteristics of genotype and phenotype in Chinese patients with Bardet-Biedl syndrome

PURPOSE

To investigate complex and different phenotypes in seven Chinese patients diagnosed with Bardet-Biedl syndrome (BBS) and carrying pathogenic mutations.

METHODS

Seven unrelated BBS patients were enrolled. Their medical and ophthalmic histories were reviewed, and comprehensive clinical examinations, such as fundus photography, optical coherence tomography, and medical imaging, were performed. A specific hereditary eye disease enrichment panel based on exome-capture technology was used to collect and amplify the protein-coding regions of 441 targeted hereditary eye disease genes, followed by high-throughput sequencing using the Illumina HiSeq platform.

RESULTS

All patients exhibited the primary clinical phenotype of BBS. Seven BBS mutations were found in five patients (BBS7 in two patients, BBS10 in two patients, BBS12 in one patient), for a detection rate of 71% (5/7). The ratio of novel to known BBS mutations was 5:2.

CONCLUSIONS

This study showed the phenotypic and genotypic spectrum of BBS patients from China, and the findings underscore the importance of obtaining comprehensive clinical observations and molecular analyses for ciliopathies.

Predominantly Cone-System Dysfunction as Rare Form of Retinal Degeneration in Patients With Molecularly Confirmed Bardet-Biedl Syndrome

PURPOSE

To describe a series of patients with Bardet-Biedl syndrome (BBS) and predominantly retinal cone dysfunction, a previously only rarely reported association.

DESIGN

Retrospective observational case series.

METHODS

Seven patients with clinically proven Bardet-Biedl syndrome had undergone detailed ocular phenotyping, which included fundus examination, Goldmann visual fields, fundus autofluorescence imaging (FAF), optical coherence tomography (OCT), and electroretinography (ERG). Mutational screening in the BBS genes was performed either by direct Sanger sequencing or targeted next-generation sequencing.

RESULTS

All 7 patients had proven BBS mutations; 1 had a cone dystrophy phenotype on ERG and 6 had a cone-rod pattern of dysfunction. Macular atrophy was present in all patients, usually with central hypofluorescence surrounded by a continuous hyperfluorescent ring on fundus autofluorescence imaging. OCT confirmed loss of outer retinal structure within the atrophic areas. No clear genotype-phenotype relationship was evident.

CONCLUSIONS

Patients with Bardet-Biedl syndrome usually develop early-onset retinitis pigmentosa. In contrast, the patients described herein, with molecularly confirmed Bardet-Biedl syndrome, developed early cone dysfunction, including the first reported case of a cone dystrophy phenotype associated with the disorder. The findings significantly expand the phenotype associated with Bardet-Biedl syndrome.

In search of triallelism in Bardet-Biedl syndrome

Bardet-Biedl syndrome (BBS) is a model disease for ciliopathy in humans. The remarkable genetic heterogeneity that characterizes this disease is consistent with accumulating data on the interaction between the proteins encoded by the 14 BBS genes identified to date. Previous reports suggested that such interaction may also extend to instances of oligogenic inheritance in the form of triallelism which defies the long held view of BBS as an autosomal recessive disease. In order to investigate the magnitude of triallelism in BBS, we conducted a comprehensive analysis of all 14 BBS genes as well as the CCDC28B-modifier gene in a cohort of 29 BBS families, most of which are multiplex. Two in trans mutations in a BBS gene were identified in each of these families for a total of 20 mutations including 12 that are novel. In no instance did we observe two mutations in unaffected members of a given family, or observe the presence of a third allele that convincingly acted as a modifier of penetrance and supported the triallelic model of BBS. In addition to presenting a comprehensive genotype/phenotype overview of a large set of BBS mutations, including the occurrence of nonsyndromic retinitis pigmentosa in a family with a novel BBS9 mutation, our study argues in favor of straightforward autosomal recessive BBS in most cases.

Visual acuity and retinal function in patients with Bardet-Biedl syndrome

OBJECTIVE

Bardet-Biedl syndrome is a genetic, multisystem disorder that causes severe visual impairment. This condition is characterized by retinal dystrophy, obesity, digit anomalies, renal disease, and hypogonadism. The purpose of this study was to analyze visual acuity and full-field electroretinogram findings in patients with the Bardet-Biedl syndrome phenotype.

METHODS

The visual acuity of a group of 23 patients (15 males) with ages ranging from 6-36 years (mean = 15.8 ± 6.4; median = 14.7) was assessed. Retinal function was evaluated by full-field electroretinography, and dark-adapted thresholds were assessed.

RESULTS

Visual acuity in the better-seeing eye was 20/40 or better in 5 patients (21.7%), 20/50-20/150 in 13 (56.5%) patients, 20/200-20/400 in 2 (8.7%) patients and worse than 20/400 in one (4.3%) patient. The mean acuity in the better-seeing eye was 0.7 ± 0.6 logMAR (20/100, Snellen equivalent). Scotopic rod and maximal responses were nondetectable in 21 (91.3%) patients, and cone responses were non-detectable in 15 (65.2%) patients. Elevated dark-adapted visual thresholds were observed in all 19 patients who were able to be assessed, with 10 (52.6%) patients having thresholds greater than 30 dB.

CONCLUSIONS

In a relatively young cohort of patients with Bardet-Biedl syndrome, only 21% had 20/40 or better vision. ERG scotopic responses were absent in the majority of cases, with cone responses being observed in less than half of cases. These findings showed the early deleterious effects in retinal function and visual acuity caused by this condition.

Impaired photoreceptor protein transport and synaptic transmission in a mouse model of Bardet-Biedl syndrome

Bardet-Biedl syndrome (BBS) is an oligogenic syndrome whose manifestations include retinal degeneration, renal abnormalities, obesity and polydactylia. Evidence suggests that the main etiopathophysiology of this syndrome is impaired intraflagellar transport (IFT). In this study, we study the Bbs4-null mouse and investigate photoreceptor structure and function after loss of this gene. We find that Bbs4-null mice have defects in the transport of phototransduction proteins from the inner segments to the outer segments, before signs of cell death. Additionally, we show defects in synaptic transmission from the photoreceptors to secondary neurons of the visual system, demonstrating multiple functions for BBS4 in photoreceptors.

[Update on Bardet-Biedl syndrome]

Until recently, Bardet-Biedl syndrome was considered as a classic autosomal recessive condition. The disorder is defined by the association of the following clinical features: retinitis pigmentosa, polydactyly, obesity, hypogonadism, and possible mental retardation. This syndrome leads to multiple handicaps (visual impairment, complications of obesity, kidney failure, endocrine dysfunction). This condition, apparently clearly defined from a clinical point of view, appears to be genetically heterogenous. To date, six different genes have been identified: BBS1, BBS2, BBS4, BBS6, BBS7 and BBS8. Interestingly, this condition has recently been linked to a failure of cellular ciliogenesis. Moreover, this disorder is characterized by an additional degree of complexity, as it is the first example of triallelic inheritance described in human beings. However, this new finding appears to be less frequent than expected in this syndrome.