Recurrence risks for Bardet-Biedl syndrome: Implications of locus heterogeneity

The characterization and comorbidities of heterozygous Bardet-Biedl syndrome carriers

Introduction: Bardet-Biedl syndrome (BBS) is a rare autosomal recessive disorder with clinical features of retinal dystrophy, obesity, postaxial polydactyly, renal anomalies, learning disabilities, hypogonadism, and genitourinary abnormalities. Nevertheless, previous studies on the phenotypic traits of BBS heterozygous carriers have generated inconclusive results. The aim of our study was to investigate the impact of BBS heterozygosity on carriers when compared to non-carriers within the Taiwanese population. Materials and Methods: This study follows a hospital-based case-control design. We employed the Taiwan Biobank version 2 (TWBv2) array to identify three specific loci associated with BBS (rs773862084, rs567573386, and rs199910690). In total, 716 patients were included in the case group, and they were compared to a control group of 2,864 patients who lacked BBS alleles. The control group was selected through gender and age matching at a ratio of 1:4. The association between BBS-related loci and comorbidity was assessed using logistic regression models. Results: We found that BBS heterozygous carriers exhibited a significant association with elevated BMI levels, especially the variant rs199910690 in MKS1 (p=0.0037). The prevalence of comorbidities in the carriers' group was not higher than that in the non-carriers' group. Besides, the average values of the biochemistry data showed no significant differences, except for creatinine level. Furthermore, we conducted a BMI-based analysis to identify specific risk factors for chronic kidney disease (CKD). Our findings revealed that individuals carrying the CA/AA genotype of the BBS2 rs773862084 variant or the CT/TT genotype of the MKS1 rs199910690 variant showed a reduced risk of developing CKD, irrespective of their BMI levels. When stratified by BMI level, obese males with the MKS1 rs199910690 variant and obese females with the BBS2 rs773862084 variant exhibited a negative association with CKD development. Conclusion: We found that aside from the association with overweight and obesity, heterozygous BBS mutations did not appear to increase the predisposition of individuals to comorbidities and metabolic diseases. To gain a more comprehensive understanding of the genetic susceptibility associated with Bardet-Biedl Syndrome (BBS), further research is warranted.

Prevalence of genetic causes of obesity in clinical practice

Background

While obesity is common in the United States, monogenic obesity is rare, accounting for approximately 5% of individuals with obesity. New targeted therapies for genetic forms of obesity are available but there is limited guidance on who requires testing. The aims of this study were to evaluate the prevalence of potentially clinically significant variants among individuals in Pediatric Endocrinology or Medical Weight Center clinics at a single center and to identify clinical characteristics that may make genetic obesity more likely.

Methods

Children and adults who had a genetic test for obesity, Uncovering Rare Obesity Gene panel, ordered during routine clinic visits from December 2019 to March 2021 were identified.

Results

Of the 139 patients with testing ordered, 117 had available results and clinical data. Over 40% (52/117, 44%) had at least one positive result (variant) with a variant that is considered pathogenic, likely pathogenic, or a variant of uncertain significance. No association was detected between age, sex, race, and body mass index (BMI) or BMI z-score with a variant. Twenty-six individuals (22%) had one or more variants in genes associated with Bardet Biedl Syndrome, and 8 (6.8%) of them had pathogenic variants, higher than expected.

Conclusion

Overall, clinical suspicion for genetic obesity is important in determining who requires genetic testing but no clinical factors were found to predict results. While obesity is multifactorial, novel medications for genetic forms of obesity indicate the need for evidence-based guidelines for who requires genetic testing for obesity.

Testing for rare genetic causes of obesity: findings and experiences from a pediatric weight management program

BACKGROUND

Genetic screening for youth with obesity in the absence of syndromic findings has not been part of obesity management. For children with early onset obesity, genetic screening is recommended for those having clinical features of genetic obesity syndromes (including hyperphagia).

OBJECTIVES

The overarching goal of this work is to report the findings and experiences from one pediatric weight management program that implemented targeted sequencing analysis for genes known to cause rare genetic disorders of obesity.

SUBJECTS/METHODS

This exploratory study evaluated youth tested over an 18-month period using a panel of 40-genes in the melanocortin 4 receptor pathway. Medical records were reviewed for demographic and visit information, including body mass index (BMI) percent of 95th percentile (%BMIp95) and two eating behaviors.

RESULTS

Of 117 subjects: 51.3% were male; 53.8% Hispanic; mean age 10.2 years (SD 3.8); mean %BMIp95 157% (SD 29%). Most subjects were self- or caregiver-reported to have overeating to excess or binge eating (80.3%) and sneaking food or eating in secret (59.0%). Among analyzed genes, 72 subjects (61.5%) had at least one variant reported; 50 (42.7%) had a single variant reported; 22 (18.8%) had 2-4 variants reported; most variants were rare (<0.05% minor allele frequency [MAF]), and of uncertain significance; all variants were heterozygous. Nine subjects (7.7%) had a variant reported as PSCK1 "risk" or MC4R "likely pathogenic"; 39 (33.3%) had a Bardet-Biedl Syndrome (BBS) gene variant (4 with "pathogenic" or "likely pathogenic" variants). Therefore, 9 youth (7.7%) had gene variants previously identified as increasing risk for obesity and 4 youth (3.4%) had BBS carrier status.

CONCLUSIONS

Panel testing identified rare variants of uncertain significance in most youth tested, and infrequently identified variants previously reported to increase the risk for obesity. Further research in larger cohorts is needed to understand how genetic variants influence the expression of non-syndromic obesity.

Laurence-Moon-Bardet-Biedl Syndrome with Coexisting Abdominal Distension and Positive Fluid Thrill: A Rare Manifestation Reported in Karachi, Pakistan

Laurence-Moon-Bardet-Biedl syndrome (LMBBS) is a rare autosomal recessive (AR) disorder. It is characterized predominantly by hypogonadism, polydactyly, retinitis pigmentosa, obesity, and mental retardation. Herein, we present a classic case of LMBBS with generalized body edema, abdominal distension, and positive fluid thrill in a 32-year-old male. LMBBS patients are friendly with a happy predisposition, proper management, and regular examinations should be done in order to maintain healthy organ function and to avoid an early death. Renal failure is the most common cause of mortality in LMBBS patients.

Identification of A Novel Compound Heterozygous Mutation in BBS12 in An Iranian Family with Bardet-Biedl Syndrome Using Targeted Next Generation Sequencing

Bardet-Biedl syndrome (BBS) is a pleiotropic and multisystemic disorder characterized by rod-cone dystrophy, polydactyly, learning difficulties, renal abnormalities, obesity and hypogonadism. This disorder is genetically heterogeneous. Until now, a total of nineteen genes have been identified for BBS whose mutations explain more than 80% of diagnosed cases. Recently, the development of next generation sequencing (NGS) technology has accelerated mutation screening of target genes, resulting in lower cost and less time consumption. Here, we screened the most common BBS genes (BBS1-BBS13) using NGS in an Iranian family of a proposita displaying symptoms of BBS. Among the 18 mutations identified in the proposita, one (BBS12 c.56T>G and BBS12 c.1156C>T) was novel. This compound heterozygosity was confirmed by Sanger sequencing in the proposita and her parents. Although our data were presented as a case report, however, we suggest a new probable genetic mechanism other than the conventional autosomal recessive inheritance of BBS. Additionally, given that in some Iranian provinces, like Khuzestan, consanguineous marriages are common, designing mutational panels for genetic diseases is strongly recommended, especially for those with an autosomal recessive inheritance pattern.

Bardet-Biedl syndrome with vulva carcinoma presented with acute renal failure: a case report

BACKGROUND

Bardet-Biedl syndrome is a rare disorder characterized by retinal dystrophy, obesity, kidney dysfunction, polydactyly, hypogonadism and cognitive impairment. It can be accompanied by systemic findings such as malignancy, hypertension, diabetes mellitus, constitutional and functional disorders of urogenital system and liver fibrosis.

CASE REPORT

A 35-year-old woman with Bardet-Biedl syndrome was referred to our outpatient nephrology clinic with dysuria, acute renal failure, and urinary tract infection. A sized 2 x 1 cm mass between labia major and minor was noted, while CT scan showed a lesion that encompassed uterus and extended to the posterior side of the bladder in the left adnexal region and a 3 cm lesion in the liver. Excisional biopsy of the mass revealed a well-differentiated, squamous cell carcinoma. Dysuria resolved with insertion of urinary catheter after bougie dilatation and the patient was referred for radiotherapy.

CONCLUSION

It should be kept in the mind that renal failure may develop due to constitutional urogenital anomalies such as vulva carcinoma. This can be an important cause of morbidity and mortality in patients with Bardet-Biedl syndrome.Hippokratia 2015; 19 (2):176-178.

Cognitive, sensory, and psychosocial characteristics in patients with Bardet-Biedl syndrome

Forty-two patients with a clinical diagnosis of Bardet-Biedl syndrome ages 2-61 years were given a neuropsychological test battery to evaluate cognitive, sensory, and behavioral functioning. These tests included the Wechsler scales of intelligence, Rey Auditory Verbal Learning Test, Boston Naming Test, D-KEFS Verbal Fluency Test, D-KEFS Color-Word Interference Test, D-KEFS Sorting Test, Wide Range Achievement Test: Math and Reading Subtests, Purdue Pegboard, The University of Pennsylvania Smell Identification Test, Social Communication Questionnaire, Social Responsiveness Scale, and Behavior Assessment System for Children, Second Edition, Parent Rating Scale. On the age appropriate Wechsler scale, the mean Verbal Comprehension was 81 (n = 36), Working Memory was 81 (n = 36), Perceptual Reasoning was 78 (n = 24) and Full Scale IQ was 75 (n = 26). Memory for a word list (Rey Auditory Verbal Learning Test) was in the average range with a mean of 89 (n = 19). Fine motor speed was slow on the Purdue with mean scores 3-4 standard deviations below norms. All subjects were microsmic on the University of Pennsylvania Smell Identification Test. Of these 42 patients, only 6 were able to complete all auditory and visual tests; 52% were unable to complete the visual tests due to impaired vision. A wide range of behavioral issues were endorsed on questionnaires given to parents. Most had social skill deficits but no pattern of either externalizing or internalizing problems. We identify a characteristic neuro-behavioral profile in our cohort comprised of reduced IQ, impaired fine-motor function, and decreased olfaction.

Taurodontism: A minor diagnostic criterion in Laurence-Moon/Bardet-Biedl syndromes

OBJECTIVE

The objective of the study was to present the prevalence of taurodontism in the permanent dentition in individuals with Laurence-Moon/Bardet-Biedl syndromes (LM/BBS).

METHODS AND PARTICIPANTS

Thirty-nine individuals were studied, which comprises the whole population of known LM/BBS patients in Norway. Data were collected retrospectively. Panoramic radiographs (OPG) were evaluated to document taurodontism.

RESULTS

Taurodontism was found in 82.9% of the individuals with LM/BBS. The second mandibular molars had the highest (72.3%) prevalence of taurodontism and the first mandibular molars the lowest (58.2%).

CONCLUSION

This study suggests that taurodontism should be included as a minor diagnostic criterion for the Laurence-Moon/Bardet-Biedl syndromes (LM/BBS).

Molecular analysis of Bardet-Biedl syndrome families: report of 21 novel mutations in 10 genes

PURPOSE

Bardet-Biedl syndrome (BBS) is genetically heterogeneous with 15 BBS genes currently identified, accounting for approximately 70% of cases. The aim of our study was to define further the spectrum of BBS mutations in a cohort of 44 European-derived American, 8 Tunisian, 1 Arabic, and 2 Pakistani families (55 families in total) with BBS.

METHODS

A total of 142 exons of the first 12 BBS-causing genes were screened by dideoxy sequencing. Cases in which no mutations were found were then screened for BBS13, BBS14, BBS15, RPGRIP1L, CC2D2A, NPHP3, TMEM67, and INPP5E.

RESULTS

Forty-three mutations, including 8 frameshift mutations, 10 nonsense mutations, 4 splice site mutations, 1 deletion, and 20 potentially or probably pathogenic missense variations, were identified in 46 of the 55 families studied (84%). Of these, 21 (2 frameshift mutations, 4 nonsense mutations, 4 splice site mutations, 1 deletion, and 10 missense variations) were novel. The molecular genetic findings raised the possibility of triallelic inheritance in 7 Caucasian families, 1 Arabian family, and 1 Tunisian patient. No mutations were detected for BBS4, BBS11, BBS13, BBS14, BBS15, RPGRIP1L, CC2D2A, NPHP3, TMEM67, or INPP5E.

CONCLUSIONS

This mutational analysis extends the spectrum of known BBS mutations. Identification of 21 novel mutations highlights the genetic heterogeneity of this disorder. Differences in European and Tunisian patients, including the high frequency of the M390R mutation in Europeans, emphasize the population specificity of BBS mutations with potential diagnostic implications. The existence of some BBS cases without mutations in any currently identified BBS genes suggests further genetic heterogeneity.