Paroxysmal Kinesigenic Dyskinesia Caused by 16p11.2 Microdeletion and Related Clinical Features.

BACKGROUND AND OBJECTIVES: Isolated paroxysmal kinesigenic dyskinesia (PKD) is mainly caused by PRRT2 variants and TMEM151A variants. Patients with proximal 16p11.2 microdeletion (16p11.2MD) (including PRRT2) often have neurodevelopmental phenotypes, whereas a few patients have PKD. Here, we aimed to identify 16p11.2MD in patients with PKD and describe the related phenotypes. METHODS: Whole-exome sequencing and bioinformatics analysis of copy number variant (CNV) were performed in patients with PKD carrying neither PRRT2 nor TMEM151A variant. Quantitative PCR and low-coverage whole-genome sequencing verified the CNV. RESULTS: We identified 9 sporadic patients with PKD and 16p11.2MD (∼535 kb), accounting for 9.6% (9/94) of our patients. Together with 9 previously reported patients with PKD and 16p11.2MD, we found that 16p11.2MD was de novo in 11 of 12 tested patients and inherited from a parent in the other patient. And 80% (12/15) of these patients had a mild language delay, 64.3% (9/14) had compromised learning ability, 42.9% (6/14) had a mild motor delay, and 50% (6/12) had abnormal neuroimaging findings. No severe autism disorders were observed. DISCUSSION: Mild developmental problems may be overlooked. A detailed inquiry of developmental history and CNV testing are necessary to distinguish patients with 16p11.2MD from isolated PKD.

Functional study and pathogenicity classification of PRRT2 missense variants in PRRT2-related disorders.

AIMS: PRRT2 variants are associated with various paroxysmal disorders. To date, more than 90 PRRT2 variants have been reported in PRRT2-related disorders. Lack of functional study in majority of missense variants makes their pathogenicity uncertain. We aim to evaluate the clinical significance of PRRT2 missense variants by performing in vitro experiments. METHODS: We systematically reviewed PRRT2-related disorders and summarized reported PRRT2 missense variants. Protein expression and subcellular localization of mutant PRRT2 were investigated in mammal cells. American College of Medical Genetics and Genomics (ACMG) guidelines were used to analyze the pathogenicity of PRRT2 missense variants. RESULTS: A total of 29 PRRT2 missense variants were identified in PRRT2-related disorders. Ten variants were observed to affect both subcellular localization and protein level, three variants only affect membrane localization, and two variants only affect protein level. According to ACMG guidelines, 15 variants were finally classified as "likely pathogenic", three as "benign", three as "likely benign", and eight as "uncertain significance" variants. The likely pathogenic variants were concentrated in the C-terminal of PRRT2. CONCLUSIONS: The pathogenicity of eight uncertain significance variants needs further investigation. C-terminal of PRRT2 is crucial for its physiological function.

Clinical features of Chinese patients with Gerstmann-Sträussler-Scheinker identified by targeted next-generation sequencing.

Gerstmann-Sträussler-Scheinker (GSS) is an autosomal dominant neurodegenerative disease due to mutations within prion protein (PRNP) gene. Clinically, it is not easy to distinguish GSS from spinocerebellar ataxia (SCA), especially in the early stage of disease. We aimed to identify genetic mutations in 8 Chinese pedigrees with dominant ataxia but excluded dynamic mutations of SCA genes. Targeted next-generation sequencing was performed in the 8 probands. A customized panel was designed to capture 24 known causative genes, including 15 autosomal dominant SCA genes and 9 dementia-related genes. A 2-year follow-up was performed in these patients who harbored mutation. Of the 8 probands, 5 were identified to harbor the p.P102L mutation within PRNP. All these 5 cases had progressive ataxia with age at onset ranging from 48 to 52 years (49.5 ± 4.51). Remarkable phenotypic heterogeneity was observed in them. Cognitive decline was found in 4/5 probands. The average duration from initial symptoms to cognitive decline is 32.5 months, ranging from 22 to 48 months. In this study, we presented the detailed clinical features of 5 GSS pedigrees with PRNP p.P102L mutation. The variable phenotypes among these GSS patients indicated other genetic or environmental factors might be involved in the phenotypic heterogeneity of GSS. Our findings also support the proposal that screening of PRNP mutations should be performed for the patients with dominant ataxia if dynamic mutations of SCA genes were excluded.

Improving molecular diagnosis of Chinese patients with Charcot-Marie-Tooth by targeted next-generation sequencing and functional analysis.

Charcot-Marie-Tooth (CMT) disease is the most common hereditary peripheral neuropathy. More than 50 causative genes have been identified. The lack of genotype-phenotype correlations in many CMT patients make it difficult to decide which genes are affected. Recently, targeted next-generation sequencing (NGS) has been introduced as an alternative approach for diagnosis of genetic disorders. Here, we applied targeted NGS in combination with PMP22 duplication/deletion analysis to screen causative genes in 22 Chinese CMT families. The novel variants detected by targeted NGS were then further studied in cultured cells. Of the 22 unrelated patients, 8 had PMP22 duplication. The targeted NGS revealed 10 possible pathogenic variants in 11 patients, including 7 previously reported variants and 3 novel heterozygous variants (GJB1: p.Y157H; MFN2: p.G127S; YARS: p.V293M). Further classification of the novel variants according to American College of Medical Genetics and Genomics (ACMG) standards and guidelines and functional analysis in cultured cells indicated that p.Y157H in GJB1 was pathogenic, p.G127S in MFN2 was likely pathogenic, while p.V293M in YARS was likely benign. Our results suggest the potential for targeted NGS to make a more rapid and precise diagnosis in CMT patients. Moreover, the functional analysis is required when the novel variants are indistinct.

[Spatiotemporal expression pattern of E-cadherin and P-cadherin during mouse tooth development].

OBJECTIVE: To investigate the expression patterns of E-cadherin and P-cadherin in murine-tooth germs at early developmental stages. METHODS: Mandible samples of CD1 mice from embryonic day 12.5 to postnatal day 3.5 were collected. The expressions of E-cadherin and P-cadherin in murine mandibular first molar germs were detected by immunofluorescence and observed under confocal fluorescence microscope. HE staining was performed for tissue morphology. RESULTS: Both E-cadherin and P-cadherin were widely expressed in the epithelial tissues through early developmental stages. The E-cadherin expression was increased in polarizing pre-ameloblasts, whereas the P-cadherin expression declined. The expression of the P-cadherin could be detected in epithelial tissues before bud stage, and expressed in mature ameloblasts at secretory stage. CONCLUSION: The E-cadherin and P-cadherin expressed in different spatiotemporal expression patterns, indicating their individual functions during tooth development. P-cadherin might function in the secretion and mineralization of enamel.