A novel missense mutation of RYR1 in familial idiopathic hyper CK-emia

Area of Science:

• Genetics
• Molecular Biology
• Biochemistry

Background:

• Idiopathic hyper creatine kinase (IHCK) is defined by persistently elevated serum creatine kinase (CK) levels without apparent symptoms.
• Familial forms of IHCK suggest a genetic basis, necessitating the identification of causative genes.

Purpose of the Study:

• To investigate the genetic underpinnings of familial idiopathic hyper creatine kinase (IHCK) in a Japanese pedigree.
• To identify specific genetic variants associated with IHCK and elucidate their functional impact.

Main Methods:

• Conducted a four-generation pedigree analysis using multipoint linkage analysis.
• Performed exome sequencing to identify genetic variants, followed by filtering processes.
• Validated the identified variant's association with IHCK through cosegregation analysis and in silico predictions (Mutation Taster, PolyPhen-2, PANTHER).
• Assessed RYR1 gene and protein expression levels in patient biopsy samples using immunohistochemistry, Western blotting, and real-time RT-PCR.

Main Results:

• Identified a novel heterozygous nonsynonymous single nucleotide variant (SNV), c.7034G>C, p.S2345T, in the RYR1 gene that cosegregated with IHCK in the pedigree.
• In silico analyses predicted the SNV as disease-causing and damaging.
• Confirmed the SNV's absence in 511 healthy Japanese individuals, ruling out a common polymorphism.
• Demonstrated significantly reduced RYR1 protein and mRNA expression levels in patients carrying the variant.

Conclusions:

• The novel RYR1 SNV (c.7034G>C, p.S2345T) is strongly associated with idiopathic hyper creatine kinase (IHCK).
• The identified variant likely contributes to IHCK pathogenesis through a dominant negative effect, leading to reduced RYR1 expression.
• This study identifies RYR1 as a gene responsible for certain forms of IHCK.