Two novel B9D1 variants causing Joubert syndrome: Utility of mRNA and splicing studies

The primary cilium is an organelle which plays an important role in the transduction of signals in the Wnt and Sonic hedgehog pathways. Abnormal or absent primary cilia result in various neurodevelopmental, retinal, renal, hepatic and musculoskeletal abnormalities. Joubert syndrome (JS) is a ciliopathy with a prevalence estimated to be between 1:80 000 and 1:100 000. JS occurs due to bi-allelic mutations in one of the 34 identified genes, all of which encode for protein components of the primary cilia. The presentation of JS is highly variable, however a clinical diagnosis can be established by the presence of the molar tooth sign on axial brain MRI, hypotonia in infancy, and developmental delay. JS is less severe than Meckel syndrome (MKS), which is another recessive, and often lethal, ciliopathy. This report outlines an interesting case of JS, in which two novel mutations in B9D1 were identified. This gene is not commonly associated with JS, and is often implicated in MKS. Functional mRNA study was helpful in delineating the pathogenic role of novel variants in this case.     

Expanding the phenotype of males with OFD1 pathogenic variants-a case report and literature review

Pathogenic variants in the OFD1 gene have been classically associated with the Orofaciodigital syndrome type 1 in females, a condition previously considered to be X-linked dominant with male embryonic lethality. However, an increasing number of males with pathogenic OFD1 variants who survived beyond the neonatal period have now been reported in the literature. Although each new report has added to the ever-broadening spectrum of clinical findings seen in males, many questions about genotype-phenotype correlations and disease mechanism remain. Herein, we describe a 9-year-old male child with a novel hemizygous pathogenic OFD1 variant identified by exome sequencing and a unique combination of findings, not previously reported, including presence of both a hypothalamic hamartoma and the molar tooth sign. His clinical features overlap multiple ciliopathy phenotypes, blurring the boundaries of distinct ciliopathy gene-disease relationships. This case provides further evidence for the consideration of a broad OFD1-relateddisorder spectrum in affected males rather than multiple distinct phenotypes. Additionally, a review of previously published cases of the disorder in males support the inclusion of the OFD1 gene in the differential diagnosis and work up for all individuals who present with primary ciliopathy-type features, regardless of their gender. We also highlight current information about OFD1 variant types and pathogenesis and explore how these could mechanistically drive some of the observed phenotypic differences.     

Novel Mutations Including Deletions of the Entire OFD1 Gene in 30 Families with Type 1 Orofaciodigital Syndrome: A Study of the Extensive Clinical Variability

OFD1, now recognized as a ciliopathy, is characterized by malformations of the face, oral cavity and digits, and is transmitted as an X‐linked condition with lethality in males. Mutations in OFD1 also cause X‐linked Joubert syndrome (JBTS10) and Simpson–Golabi–Behmel syndrome type 2 (SGBS2). We have studied 55 sporadic and six familial cases of suspected OFD1. Comprehensive mutation analysis in OFD1 revealed mutations in 37 female patients from 30 families; 22 mutations have not been previously described including two heterozygous deletions spanning OFD1 and neighbouring genes. Analysis of clinical findings in patients with mutations revealed that oral features are the most reliable diagnostic criteria. A first, detailed evaluation of brain MRIs from seven patients with cognitive defects illustrated extensive variability with the complete brain phenotype consisting of complete agenesis of the corpus callosum, large single or multiple interhemispheric cysts, striking cortical infolding of gyri, ventriculomegaly, mild molar tooth malformation and moderate to severe cerebellar vermis hypoplasia. Although the OFD1 gene apparently escapes X‐inactivation, skewed inactivation was observed in seven of 14 patients. The direction of skewing did not correlate with disease severity, reinforcing the hypothesis that additional factors contribute to the extensive intrafamilial variability.     

BAZ1B is a candidate gene responsible for hypothyroidism in Williams syndrome

Williams syndrome (WS) is a rare neurodevelopmental disorder associated to a hemizygous deletion of 28 genes located on chromosome 7q11.23. WS affected subjects frequently suffer from several endocrine abnormalities including hypothyroidism due to defects in thyroid morphology. To date, several genes involved in thyroid dysgenesis have been identified, nonetheless, none of them is located in the 7q11.23 region. Thus, the hypothyroidism-linked molecular features in WS are not yet known. In this study we focused on one of the WS deleted gene, BAZ1B, demonstrating that its downregulation in thyroid cells leads to cell viability and survival decrement. Taking together, our results show that BAZ1B could be the mainly responsible for thyroid defects observed in some of WS patients and that these alterations are activated by PTEN-mediated mechanisms.     

Alström Syndrome: Mutation Spectrum of ALMS1

Alström Syndrome (ALMS), a recessive, monogenic ciliopathy caused by mutations in ALMS1, is typically characterized by multisystem involvement including early cone‐rod retinal dystrophy and blindness, hearing loss, childhood obesity, type 2 diabetes mellitus, cardiomyopathy, fibrosis, and multiple organ failure. The precise function of ALMS1 remains elusive, but roles in endosomal and ciliary transport and cell cycle regulation have been shown. The aim of our study was to further define the spectrum of ALMS1 mutations in patients with clinical features of ALMS. Mutational analysis in a world‐wide cohort of 204 families identified 109 novel mutations, extending the number of known ALMS1 mutations to 239 and highlighting the allelic heterogeneity of this disorder. This study represents the most comprehensive mutation analysis in patients with ALMS, identifying the largest number of novel mutations in a single study worldwide. Here, we also provide an overview of all ALMS1 mutations identified to date.     

Aberrant splicing is a common mutational mechanism in MKS1, a key player in Meckel-Gruber syndrome

Meckel-Gruber syndrome (MKS) is an autosomal recessive, usually lethal multisystemic disorder characterized by early developmental anomalies of the central nervous system, cystic kidney dysplasia, hepatobiliary ductal plate malformation, and postaxial polydactyly. Three MKS loci have been mapped and recently, two genes were identified: MKS1 on 17q22 in Caucasian kindreds and MKS3 on 8q22 in Omani and Pakistani families, putting MKS on the growing list of ciliary disorders ("ciliopathies"). We performed linkage analysis for MKS1-3 in 14 consanguineous and/or multiplex families of different ethnic origins with histologic diagnosis and at least three classic MKS manifestations in each kindred. Unexpectedly, only five families were linked to any of the known MKS loci, clearly indicating further locus heterogeneity. All five families showed homozygosity for MKS1 and, intriguingly, were of non-Caucasian origin. MKS1 sequencing revealed no mutation in two of these pedigrees, whereas different, novel splicing defects were identified in the three other families and an additional sporadic German patient. Given that all of our mutations and two of the in total four known MKS1 changes cause aberrant splicing (while the other two known mutations were frameshift mutations), we hypothesize that splicing defects are a crucial mutational mechanism in MKS1 which apparently is one of the main loci and key players in MKS. Our results indicate that MKS1 mutations are not restricted to the Caucasian gene pool and suggest further genetic heterogeneity for MKS. Overall, our data have immediate implications for genetic counselling and testing approaches in MKS.     

AHI1 mutations cause both retinal dystrophy and renal cystic disease in Joubert syndrome

Background

Joubert syndrome (JS) is an autosomal recessive disorder characterised by hypotonia, ataxia, mental retardation, altered respiratory pattern, abnormal eye movements, and a brain malformation known as the molar tooth sign (MTS) on cranial MRI. Four genetic loci have been mapped, with two genes identified (AHI1 and NPHP1).

Methods

We screened a cohort of 117 JS subjects for AHI1 mutations by a combination of haplotype analysis and sequencing of the gene, and for the homozygous NPHP1 deletion by sequencing and marker analysis.

Results

We identified a total of 15 novel AHI1 mutations in 13 families, including nonsense, missense, splice site, and insertion mutations, with some clustering in the WD40 domains. Eight families were consanguineous, but no single founder mutation was apparent. In addition to the MTS, retinal dystrophy was present in 11 of 12 informative families; however, no subjects exhibited variable features of JS such as polydactyly, encephalocele, colobomas, or liver fibrosis. In contrast to previous reports, we identified two families with affected siblings who developed renal disease consistent with nephronophthisis (NPH) in their 20s. In addition, two individuals with classic NPH were found to have homozygous NPHP1 deletions.

Conclusions

Overall, 11% of subjects had AHI1 mutations, while ∼2% had the NPHP1 deletion, representing a total of less than 15% in a large JS cohort. Some preliminary genotype‐phenotype correlations are possible, notably the association of renal impairment, specifically NPH, in those with NPHP1 deletions. Subjects with AHI1 mutations may be at risk of developing both retinal dystrophy and progressive kidney disease.     

重型乙型肝炎患者TNF和IL－1的检测及意义

检测３０例重型乙型病毒性肝炎（重型肝炎）患者血清和外周血单个核细胞（ＰＢＭＣ）培养上清中肿瘤坏死因子（ＴＮＦ）水平及ＰＢＭＣ诱生的白细胞介素１（ＩＬ－１）活性，结果：重型肝炎患者ＴＮＰ和ＩＬ－１水平均增高，且二者呈正相关。提示ＴＮＦ和ＩＬ－１在重型肝炎的发病机制中起重要作用。     

A novel HYLS1 homozygous mutation in living siblings with Joubert syndrome

The p.Asp211Gly homozygous HYLS1 mutation is so far known to cause only hydrolethalus syndrome, a lethal malformation syndrome. We report living sibling patients with a homozygous no‐stop mutation in exon 4 of HYLS1, NM_145014.2:c.900A>C (p.Ter300TyrextTer11) in the second decade of life. The proband has Joubert syndrome (JS). The younger brother also has JS and an enlarged posterior fossa that was initially diagnosed as Dandy–Walker malformation. The present mutation is unique as it affects the stop codon. The product protein HYLS1 plays an essential role in the formation of the primary cilium. This report provides insight into the spectrum of disorders involving midline brain defects closely related to cilium dysfunction or ciliopathy.     

A novel pathogenic variant in OFD1 results in X‐linked Joubert syndrome with orofaciodigital features and pituitary aplasia

Orofaciodigital syndrome type I and X‐linked recessive Joubert syndrome are known ciliopathic disorders that are caused by pathogenic variants in OFD1 gene. Endocrine system involvement with these conditions is not well described. We present the first report of a newborn male with a novel hemizygous variant in OFD1 gene c.515T>C, (p.Leu172Pro) resulting in X‐linked Joubert syndrome and orofaciodigital features with complete pituitary gland aplasia and subsequent severe hypoplasia of peripheral endocrine glands. This clinical report expands the phenotypic spectrum of endocrine system involvement in OFD1‐related disorders and suggests that OFD1 gene may be related to pituitary gland development.     

微管相关蛋白1B在FMR1基因敲除小鼠睾丸间质细胞中的表达

目的对不同周龄的Fmr1基因敲除和野生型雄性小鼠睾丸组织微管相关蛋白1B的表达进行分析比较,探讨Fmr1基因敲除小鼠的睾丸间质细胞微管相关蛋白1B表达的差异。方法采用不同周龄(4、6、8、10周)的FMR1基因敲除型(KO)和野生型(WT)各6只,先采用聚合酶链式反应(PCR)技术对KO小鼠和WT小鼠进行基因型鉴定,之后所有小鼠麻醉取睾丸组织、石蜡包埋切片进行HE染色对比观察Fmr1小鼠睾丸组织的形态,最后用免疫组织化学染色技术对KO小鼠和WT小鼠睾丸微管相关蛋白1B的表达进行检测并作对比分析。结果微管相关蛋白1B在4～10周小鼠睾丸间质细胞阳性表达,8、10周为强阳性表达,且KO小鼠在睾丸的阳性表达均高于WT小鼠。结论微管相关蛋白1B在同周龄FMR1基因敲除小鼠睾丸间质细胞的表达均显著高于WT小鼠,提示微管相关蛋白1B可能参与脆性X综合征巨睾症的发病过程。     

Homozygous missense and nonsense mutations in BMPR1B cause acromesomelic chondrodysplasia-type Grebe

Acromesomelic chondrodysplasias (ACDs) are characterized by disproportionate shortening of the appendicular skeleton, predominantly affecting the middle (forearms and forelegs) and distal segments (hands and feet). Here, we present two consanguineous families with missense (c.157T>C, p.(C53R)) or nonsense (c.657G>A, p.(W219*)) mutations in BMPR1B. Homozygous affected individuals show clinical and radiographic findings consistent with ACD-type Grebe. Functional analysis of the missense mutation C53R revealed that the mutated receptor was partially located at the cell membrane. In contrast to the wild-type receptor, C53R mutation hindered the activation of the receptor by its ligand GDF5, as shown by reporter gene assay. Further, overexpression of the C53R mutation in an in vitro chondrogenesis assay showed no effect on cell differentiation, indicating a loss of function. The nonsense mutation (c.657G>A, p.(W219*)) introduces a premature stop codon, which is predicted to be subject to nonsense-mediated mRNA decay, causing reduced protein translation of the mutant allele. A loss-of-function effect of both mutations causing recessive ACD-type Grebe is further supported by the mild brachydactyly or even non-penetrance of these mutations observed in the heterozygous parents. In contrast, dominant-negative BMPR1B mutations described previously are associated with autosomal-dominant brachydactyly-type A2.