Identification of an unknown frameshift variant of NOG in a Han Chinese family with proximal symphalangism.

Proximal symphalangism (SYM1) is an autosomal dominant disorder manifested by ankylosis of the proximal interphalangeal joints of fingers, carpal and tarsal bone fusion, and conductive hearing loss in some cases. Herein, we clinically diagnosed a Chinese patient with fusions of the bilateral proximal interphalangeal joints in the 2-5 digits without conductive hearing loss. Family history investigation revealed that his mother and grandfather also suffered from SYM1. Whole exome sequencing was performed to detect the genetic lesion of the family. The candidate gene variants were validated by Sanger sequencing. By data filtering, co-segregation analysis and bioinformatics analysis, we highly suspected that an unknown heterozygous frameshift variant (c.635_636insG, p.Q213Pfs*57) in NOG was responsible for the SYM1 in the family. This variant was predicted to be deleterious and resulted in a prolonged protein. This finding broadened the spectrum of NOG mutations associated with SYM1 and contributed to genetic diagnosis and counseling of families with SYM1.

The Novel Compound Heterozygous Mutations of ECEL1 Identified in a Family with Distal Arthrogryposis Type 5D.

INTRODUCTION: Distal arthrogryposis type 5D (DA5D) is an autosomal recessive disease. The clinical symptoms include contractures of the joints of limbs, especially camptodactyly of the hands and/or feet, unilateral ptosis, a round-shaped face, arched eyebrows, and micrognathia, without ophthalmoplegia. ECEL1 is a DA5D causative gene that encodes a membrane-bound metalloprotease. ECEL1 plays important roles in the final axonal arborization of motor nerves in limb skeletal muscles and neuromuscular junction formation during prenatal development. METHODS: A DA5D family with webbing of the elbows and fingers was recruited. We performed whole-exome sequencing (WES) and filtered mutations by disease-causing genes of arthrogryposis multiplex congenita (AMC). Mutational analysis and cosegregation confirmation were then performed. RESULTS: We identified novel compound heterozygous mutations of ECEL1 (NM_004826: c.69C>A, p.C23∗ and c.1810G>A, p.G604R) in the proband. CONCLUSIONS: We detected causative mutations in a DA5D family, expanding the spectrum of known ECEL1 mutations and contributing to the clinical diagnosis of DA5D.

Compound heterozygous GNPTAB mutations cause mucolipidosis II or III alpha/beta in two Chinese families.

OBJECTIVE: Mucolipidosis II and III alpha/beta (ML II & ML III alpha/beta) are rare autosomal recessive lysosomal storage disorders. ML II is clinically evident from birth with a progressive course and fatal outcome in childhood. The typical phenotypes of ML II include limited statural growth, craniofacial abnormality, skeletal malformation, intelligence developmental deficiency and visceral organ abnormality. ML III is milder than ML II. Mutations in GNPTAB cause the ML II/III. METHODS: Two families with ML II/III (initially undiagnosed) were recruited. We applied whole-exome sequencing (WES) and filtered mutations by genes causing lysosomal storage diseases with skeletal involvement. Mutational analysis and co-segregation confirmation were then performed. RESULTS: We presented two families with ML II or ML III alpha/beta. By WES, the compound heterozygosity of GNPTAB (c.2404C>T, p.Q802* and c.2590dup, p.E864Gfs*4) is identified in a family with ML II, and c.1364C>T, p.A455V and c.2715+1G>A are detected in a family with ML III alpha/beta. CONCLUSION: We detected the causative mutations in two ML II/III families by WES and confirmed their diagnosis of the diseases. The present identification of mutations expands the spectrum of known GNPTAB mutations and it may contribute to novel approaches to genetic diagnosis and counseling for patients with ML II/III.