Is the T-G-CT-G SNRNP70 haplotype another proof that mixed connective tissue disease is distinct from systemic lupus erythematosus and systemic sclerosis? A novel gene variant in SNRNP70 gene.

Objectives: U1-70K, encoded by the SNRNP70 gene, is a key early immunogen in connective tissue disease. The aim of the study was the genetic analysis of the SNRNP70 gene in mixed connective tissue disease (MCTD), systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) patients.

Methods: SNRNP70 genetic variants were detected using 3730 DNA Analyzer. SNRNP70 rs560811128 G/A (c.476-252 G/A), rs78616533delCT (c.475+130_475+131delCT) and rs117167710 T/C (c.393+326 T/C) variants were genotyped using the technique of sequence-specific hybridisation probe binding assays. SNRNP70 393_47 G/A mutation was detected using TaqMan SNP genotyping assay.

Results: We found one novel c.393+47G>A and three, c.476-252 G/A, c.475+130_475+131delCT and c.393+326 T/C, previously recorded variants. The present study revealed that T-G-CT-G haplotype demonstrated significantly higher frequencies in MCTD patients than in SLE and SSc patients. In MCTD patients c.475+130_475+131delCT distribution of genotype was gender-dependent and showed association with thrombo-/leukocytopenia. Mutation at position c.476-252G>A was predicted to possibly have an impact on splicing of the SNRNP70 transcript and it was present only in one MCTD patient.

Conclusions: Our results demonstrated that the T-G-CT-G SNRNP70 haplotype is another proof that MCTD may be distinct from SLE and SSc. The novel c.476-252G>A mutation in SNRNP70 gene created a new acceptor splice site and may potentially alert of splicing of the SNRNP70 transcript.