De Novo Mutations of CCNK Cause a Syndromic Neurodevelopmental Disorder with Distinctive Facial Dysmorphism.

Neurodevelopment is a transcriptionally orchestrated process. Cyclin K, a regulator of transcription encoded by CCNK, is thought to play a critical role in the RNA polymerase II-mediated activities. However, dysfunction of CCNK has not been linked to genetic disorders. In this study, we identified three unrelated individuals harboring de novo heterozygous copy number loss of CCNK in an overlapping 14q32.3 region and one individual harboring a de novo nonsynonymous variant c.331A>G (p.Lys111Glu) in CCNK. These four individuals, though from different ethnic backgrounds, shared a common phenotype of developmental delay and intellectual disability (DD/ID), language defects, and distinctive facial dysmorphism including high hairline, hypertelorism, thin eyebrows, dysmorphic ears, broad nasal bridge and tip, and narrow jaw. Functional assay in zebrafish larvae showed that Ccnk knockdown resulted in defective brain development, small eyes, and curly spinal cord. These defects were partially rescued by wild-type mRNA coding CCNK but not the mRNA with the identified likely pathogenic variant c.331A>G, supporting a causal role of CCNK variants in neurodevelopmental disorders. Taken together, we reported a syndromic neurodevelopmental disorder with DD/ID and facial characteristics caused by CCNK variations, possibly through a mechanism of haploinsufficiency.

PMP22-Related neuropathies and other clinical manifestations in Chinese han patients with charcot-marie-tooth disease type 1.

INTRODUCTION: Most cases of Charcot-Marie-Tooth (CMT) disease are caused by mutations in the peripheral myelin protein 22 gene (PMP22), including heterozygous duplications (CMT1A), deletions (HNPP), and point mutations (CMT1E). METHODS: Single-nucleotide polymorphism (SNP) arrays were used to study PMP22 mutations based on the results of multiplex ligation-dependent probe amplification (MLPA) and polymerase chain reaction-restriction fragment length polymorphism methods in 77 Chinese Han families with CMT1. PMP22 sequencing was performed in MLPA-negative probands. Clinical characteristics were collected for all CMT1A/HNPP probands and their family members. RESULTS: Twenty-one of 77 CMT1 probands (27.3%) carried duplication/deletion (dup/del) copynumber variants. No point mutations were detected. SNP array and MLPA seem to have similar sensitivity. Fifty-seven patients from 19 CMT1A families had the classical CMT phenotype, except for 1 with concomitant CIDP. Two HNPP probands presented with acute ulnar nerve palsy or recurrent sural nerve palsy, respectively. CONCLUSIONS: The SNP array has wide coverage, high sensitivity, and high resolution and can be used as a screening tool to detect PMP22 dup/del as shown in this Chinese Han population.

A novel GJB1 mutation associated with X-linked Charcot-Marie-Tooth disease in a large Chinese family pedigree.

BACKGROUND: Charcot-Marie-Tooth (CMT) disease is a group of hereditary neuropathies with high phenotypic and genetic heterogeneity. In this study, we report a large family with X-linked CMT (CMTX) caused by a novel GJB1 mutation. METHODS: A family with the clinical diagnosis of CMTX was investigated. For mutation analysis, the coding region of GJB1 was sequenced using DNA from 15 family members. The identified GJB1 mutation was investigated by DHPLC in 120 normal controls. Mutation reanalysis was performed based on whole-exome sequencing (WES). Cell transfection studies were performed to characterize the function of the novel mutation. RESULTS: A missense mutation (c.605T>A) in GJB1 was detected in five patients and eight female carriers but not in two unaffected members of the family. The mutation was not found in 120 healthy controls and has not been previously reported. WES excluded other pathogenic mutations in the family. The pathogenicity of the mutation was confirmed by disrupting the membrane localization of the encoded proteins. CONCLUSION: Our findings demonstrate that a novel mutation (c.605T>A) in GJB1 is associated with CMTX and adds to the repertoire of GJB1 mutations related to CMTX.

A novel MSX1 intronic mutation associated with autosomal dominant non-syndromic oligodontia in a large Chinese family pedigree.

BACKGROUND: Tooth agenesis is a common developmental dental anomaly. The aim of the study was to identify the causal genetic mutation in a four-generation Chinese family affected with non-syndromic autosomal dominant tooth agenesis. METHODS: Genome-wide scanning was performed using the Illumina Linkage-12 array. Genotyping of short tandem repeat markers was used to finely map the causative locus. Haplotype analysis and Sanger sequencing was performed to precisely locate the position and nature of the gene defect. RESULTS: Clinical examination of the available 23 family members showed variable tooth agenesis in 10 subjects, ranging from oligodontia to mild hypodontia. Genome-wide scanning and haplotype analyses identified the 4p16.1-p16.3 region with a maximum multi-point LOD score of 3.50, which overlapped with the MSX1 gene. A single heterozygous point mutation IVS1-5 G>A in the MSX1 gene was exclusively detected in the 10 family members affected with tooth agenesis. Sequencing of MSX1 cDNA revealed that the intronic mutation did not affect the normal splicing pattern of the pre-mRNA. However, real-time qPCR analysis of lymphocyte RNA showed that the level of MSX1 mRNA was significantly decreased in individuals heterozygous for the mutation. CONCLUSIONS: We identified and characterized a novel intronic mutation in the MSX1 gene in a large Chinese pedigree, adding to the small repertoire of MSX1 mutations associated with autosomal dominant tooth agenesis. We hypothesize that the variable degree of tooth agenesis observed in each affected individual may be due to sub-optimal levels of MSX1 expression during critical stages tooth development.

Novel de novo nonsense mutation of the PHEX gene (p.Lys50Ter) in a Chinese patient with hypophosphatemic rickets.

X-linked hypophosphatemic rickets (XLHR), the most common form of inherited rickets, is a dominant disorder characterized by hypophosphatemia, abnormal bone mineralization, and short stature. Mutations in the PHEX gene are major causes of XLHR. Herein, we clinically characterized four unrelated families with hypophosphatemia, bone abnormalities, short stature, and dentin malformation. Mutational analysis of the PHEX gene using Sanger sequencing revealed three recurrent mutations (c.2197T>C, c.1646G>C, and c.2198G>A) and a de novo nonsense mutation (c.148A>T). The novel mutation was not found in any of the unaffected family members or in the 100 healthy controls and was predicted to produce a truncated protein (p.K50X), a truncated form of the PHEX protein caused by nonsense mutations has been frequently detected in XLHR individuals. Thus, our work indicated that the c.148A>T (p.K50X) mutation was the likely pathogenic mutation in individual III-2 in family 2, and that PHEX gene mutations were responsible for XLHR in these Chinese families. These findings expand the mutation spectrum of PHEX and may help us to understand the molecular basis of XLHR in order to facilitate genetic counseling.