Whole-exome sequencing identified compound heterozygous variants in MMKS in a Chinese pedigree with Bardet-Biedl syndrome

Molecular and phenotypic characteristics of Bardet-Biedl syndrome in Chinese patients

BACKGROUND

Bardet-Biedl syndrome (BBS) is a type of non-motile ciliopathy. To date, 26 genes have been reported to be associated with BBS. However, BBS is genetically heterogeneous, with significant clinical overlap with other ciliopathies, which complicates diagnosis. Disability and mortality rates are high in BBS patients; therefore, it is urgent to improve our understanding of BBS. Thus, our study aimed to describe the genotypic and phenotypic spectra of BBS in China and to elucidate genotype-phenotype correlations.

METHODS

Twenty Chinese patients diagnosed with BBS were enrolled in this study. We compared the phenotypes of Chinese BBS patients in this study with those from other countries to analyze the phenotypic differences across patients worldwide. In addition, genotype-phenotype correlations were described for our cohort. We also summarized all previously reported cases of BBS in Chinese patients (71 patients) and identified common and specific genetic variants in the Chinese population.

RESULTS

Twenty-eight variants, of which 10 are novel, in 5 different BBS-associated genes were identified in 20 Chinese BBS patients. By comparing the phenotypes of BBSome-coding genes (BBS2,7,9) with those of chaperonin-coding genes (BBS10,12), we found that patients with mutations in BBS10 and 12 had an earlier age of onset (1.10 Vs. 2.20, p < 0.01) and diagnosis (4.64 Vs. 13.17, p < 0.01), whereas patients with mutations in BBS2, 7, and 9 had a higher body mass index (28.35 Vs. 24.21, p < 0.05) and more vision problems (p < 0.05). Furthermore, in 91 Chinese BBS patients, mutations were predominant in BBS2 (28.89%) and BBS7 (15.56%), and the most frequent variants were in BBS2: c.534 + 1G > T (10/182 alleles) and BBS7: c.1002delT (7/182 alleles), marking a difference from the genotypic spectra of BBS reported abroad.

CONCLUSIONS

We recruited 20 Chinese patients with BBS for genetic and phenotypic analyses, and identified common clinical manifestations, pathogenic genes, and variants. We also described the phenotypic differences across patients worldwide and among different BBS-associated genes. This study involved the largest cohort of Chinese patients with BBS, and provides new insights into the distinctive clinical features of specific pathogenic variants.

Review of the phenotypes and genotypes of Bardet-Biedl syndrome from China

Objective: To analyze the phenotypes, genotypes, and the relationship of phenotypes and genotypes for Chinese patients with Bardet-Biedl syndrome (BBS). Methods: The Chinese Wanfang and Weipu data, and PubMed were searched up to December 2022. Patients with detailed clinical feature data were involved in the analysis. Results: A total of 153 Chinese patients, including 87 males, 53 females, and 12 unknown, were enrolled. Their ages ranged from 1.2 to 44 years old with a mean of 16.70 ± 9.90 years old. Among these patients, 80 (52.29%) were reported by ophthalmologists, and only 24 (15.68%) reported by pediatricians. Most patients (132/137, 96.35%) had visual problems; 131/153 (85.62%) had polydactyly; 124/132 (93.93%) were overweight or obese; 63/114 (55.26%) had renal abnormalities; kidney dysfunction was found in 33 (21.57%); 83/104 (79.81%) had hypogonadism and/or genital hypoplasia; and 111/136 (81.62%) had mental retardation. In this series, genetic analysis was performed in 90 (58.82%) patients, including 22 BBS7 (24.71%), 20 BBS2 (22.73%), and 10 BBS10 (11.24%) patients. Moreover, 11 fetuses were diagnosed prenatally in the last 4 years except for one patient in 2004 year. It was noted that BBS7 had higher penetrance. BBS2 had higher hearing impairment and lower renal abnormality penetrance. BBS10 also had lower renal abnormality penetrance as well. Conclusion: Misdiagnosis or miss diagnosis of BBS may be common in China. In patients with polydactyly, visual impairment, obesity, renal abnormalities, hypogonadism, and mental retardation, or in fetuses with polydactyly and/or renal abnormalities, BBS should be considered in the differential diagnosis. Other deformities should be evaluated carefully and genetic analysis should be performed as early as possible.

Novel mutations in BBS genes and clinical characterization of Chinese families with Bardet-Biedl syndrome

PURPOSE

Bardet-Biedl syndrome (BBS) is a rare autosomal-recessive inherited disorder characterized by multisystem anomalies. The objective of this study was to detect and analyse pathogenic variants in four Chinese families with BBS.

METHODS

Comprehensive clinical examinations were performed to investigate and evaluate the phenotypes of the affected individuals from four families. Genomic DNA was extracted from peripheral blood. Next-generation sequencing (NGS) was performed for four families, and the presence of pathogenic variants was confirmed via Sanger sequencing.

RESULTS

There were two males and three females with a mean age of 16.00 years. All probands displayed the primary clinical features of BBS. Mutation screening demonstrated four novel mutations: c.613C>T; p.Q205* in the BBS5 gene, c.1391C>G; p.S464* in the BBS10 gene, and c.155delC; p.S52* and c.1584T>G; p.Y528* in the BBS12 gene. Two previously reported mutations were also identified, including c.534 + 1G>T in the BBS2 gene and c.539G>A; p.G180E in the BBS10 gene. The bioinformatic analysis revealed that all the detected mutations in BBS genes were disease causing.

CONCLUSIONS

This study identified four novel BBS gene mutations in these Chinese families and further expanded the genotypic spectrum of BBS, thus contributing to the literature and understanding of this multisystem disease.

A Novel BBS9 Mutation Identified via Whole-Exome Sequencing in a Chinese Family with Bardet-Biedl Syndrome

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder characterized by polydactyly, obesity, rod-cone dystrophy, and mental retardation. Twenty-one genes have been identified as causing BBS. This study collected a BBS pedigree from two patients and performed whole-exome sequencing on one patient. We identified a novel homozygous variant c.1114C>T (p.Q372X) in the BBS9 of the two siblings. This variant was confirmed and completely cosegregated with the disease of this family by Sanger sequencing. We report a novel homozygous variant c.1114C>T in the BBS9 gene in a Chinese family.

Ocular Characteristics of Patients With Bardet-Biedl Syndrome Caused by Pathogenic BBS Gene Variation in a Chinese Cohort

Bardet–Biedl syndrome (BBS; OMIM 209900) is a rare genetic disease causing damage to multiple organs and affecting patients’ quality of life in late adolescence or early adulthood. In this study, the ocular characteristics including morphology and function, were analyzed in 12 BBS patients from 10 Chinese families by molecular diagnostics. A total of five known and twelve novel variants in four BBS genes (BBS2, 58.33%; BBS4, 8.33%; BBS7, 16.67%; and BBS9, 16.67%) were identified in 10 Chinese families with BBS. All patients had typical phenotypes of retinitis pigmentosa with unrecordable or severely damaged cone and rod responses on full-field flash electroretinography (ffERG). Most of the patients showed unremarkable reactions in pattern visual evoked potential (PVEP) and multifocal electroretinography (mfERG), while their flash visual evoked potentials (FVEP) indicated display residual visual function. Changes in the fundus morphology, including color fundus photography and autofluorescence (AF) imaging, were heterogeneous and not consistent with the patients’ functional tests. Overall, our study expands the variation spectrum of the BBS gene, showing that the ocular characteristics of BBS patients are clinically highly heterogeneous, and demonstrates the usefulness of a combination of the ffERG and FVEP assessments of visual function in the advanced stage of retinopathy in BBS.

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.

eRAM: encyclopedia of rare disease annotations for precision medicine

Rare diseases affect over a hundred million people worldwide, most of these patients are not accurately diagnosed and effectively treated. The limited knowledge of rare diseases forms the biggest obstacle for improving their treatment. Detailed clinical phenotyping is considered as a keystone of deciphering genes and realizing the precision medicine for rare diseases. Here, we preset a standardized system for various types of rare diseases, called encyclopedia of Rare disease Annotations for Precision Medicine (eRAM). eRAM was built by text-mining nearly 10 million scientific publications and electronic medical records, and integrating various data in existing recognized databases (such as Unified Medical Language System (UMLS), Human Phenotype Ontology, Orphanet, OMIM, GWAS). eRAM systematically incorporates currently available data on clinical manifestations and molecular mechanisms of rare diseases and uncovers many novel associations among diseases. eRAM provides enriched annotations for 15 942 rare diseases, yielding 6147 human disease related phenotype terms, 31 661 mammalians phenotype terms, 10,202 symptoms from UMLS, 18 815 genes and 92 580 genotypes. eRAM can not only provide information about rare disease mechanism but also facilitate clinicians to make accurate diagnostic and therapeutic decisions towards rare diseases. eRAM can be freely accessed at http://www.unimd.org/eram/.

PedAM: a database for Pediatric Disease Annotation and Medicine

There is a significant number of children around the world suffering from the consequence of the misdiagnosis and ineffective treatment for various diseases. To facilitate the precision medicine in pediatrics, a database namely the Pediatric Disease Annotations & Medicines (PedAM) has been built to standardize and classify pediatric diseases. The PedAM integrates both biomedical resources and clinical data from Electronic Medical Records to support the development of computational tools, by which enables robust data analysis and integration. It also uses disease-manifestation (D-M) integrated from existing biomedical ontologies as prior knowledge to automatically recognize text-mined, D-M-specific syntactic patterns from 774 514 full-text articles and 8 848 796 abstracts in MEDLINE. Additionally, disease connections based on phenotypes or genes can be visualized on the web page of PedAM. Currently, the PedAM contains standardized 8528 pediatric disease terms (4542 unique disease concepts and 3986 synonyms) with eight annotation fields for each disease, including definition synonyms, gene, symptom, cross-reference (Xref), human phenotypes and its corresponding phenotypes in the mouse. The database PedAM is freely accessible at http://www.unimd.org/pedam/.

Meta-analysis of genotype-phenotype associations in Bardet-Biedl syndrome uncovers differences among causative genes

Bardet-Biedl syndrome (BBS) is a recessive genetic disease causing multiple organ anomalies. Most patients carry mutations in genes encoding for the subunits of the BBSome, an octameric ciliary transport complex, or accessory proteins involved in the BBSome assembly or function. BBS proteins have been extensively studied using in vitro, cellular, and animal models. However, the molecular functions of particular BBS proteins and the etiology of the BBS symptoms are still largely elusive. In this study, we applied a meta-analysis approach to study the genotype-phenotype association in humans using our database of all reported BBS patients. The analysis revealed that the identity of the causative gene and the character of the mutation partially predict the clinical outcome of the disease. Besides their potential use for clinical prognosis, our analysis revealed functional differences of particular BBS genes in humans. Core BBSome subunits BBS2, BBS7, and BBS9 manifest as more critical for the function and development of kidneys than peripheral subunits BBS1, BBS4, and BBS8/TTC8, suggesting that incomplete BBSome retains residual function at least in the kidney.

Whole-Genome Sequencing Identifies a Novel Variation of WAS Gene Coordinating With Heterozygous Germline Mutation of APC to Enhance Hepatoblastoma Oncogenesis

Hepatoblastoma (HB), a leading primary hepatic malignancy in children, originates from primitive hepatic stem cells. This study aimed to uncover the genetic variants that are responsible for HB oncogenesis. One family, which includes the healthy parents, and two brothers affected by HB, was recruited. Whole-genome sequencing (WGS) of germline DNA from all the family members identified two maternal variants, located within APC gene and X-linked WAS gene, which were harbored by the two brothers. The mutation of APC (rs137854573, c.C1606T, p.R536X) could result in HB carcinogenesis by activating Wnt signaling. The WAS variant (c.G3T, p.M1-P5del) could promote HB cell proliferation and inhibit T-cell-based immunity by activating PLK1 signaling and inactivating TCR signaling. Further analysis reflected that WAS deficiency might affect the antitumor activity of natural killer and dendritic cells. In summary, the obtained results imply that an APC mutant together with an X-linked WAS mutant, could lead to HB tumorigenesis by activating Wnt and PLK1 signaling, inhibiting TCR signaling, and reducing the antitumor activity of natural killer and dendritic cells.

RDAD: A Machine Learning System to Support Phenotype-Based Rare Disease Diagnosis

DNA sequencing has allowed for the discovery of the genetic cause for a considerable number of diseases, paving the way for new disease diagnostics. However, due to the lack of clinical samples and records, the molecular cause for rare diseases is always hard to identify, significantly limiting the number of rare Mendelian diseases diagnosed through sequencing technologies. Clinical phenotype information therefore becomes a major resource to diagnose rare diseases. In this article, we adopted both a phenotypic similarity method and a machine learning method to build four diagnostic models to support rare disease diagnosis. All the diagnostic models were validated using the real medical records from RAMEDIS. Each model provides a list of the top 10 candidate diseases as the prediction outcome and the results showed that all models had a high diagnostic precision (≥98%) with the highest recall reaching up to 95% while the models with machine learning methods showed the best performance. To promote effective diagnosis for rare disease in clinical application, we developed the phenotype-based Rare Disease Auxiliary Diagnosis system (RDAD) to assist clinicians in diagnosing rare diseases with the above four diagnostic models. The system is freely accessible through http://www.unimd.org/RDAD/.