CAPN3 c.1746-20C>G variant is hypomorphic for LGMD R1 calpain 3-related

Magdalena Mroczek, Inna Inashkina, Janis Stavusis, Pawel Zayakin, Andrey Khrunin, Ieva Micule, Victorija Kenina, Anna Zdanovica, Jana Zídková, Lenka Fajkusová, Svetlana Limborska, Anneke J. van der Kooi, Esther Brusse, Lea Leonardis, Ales Maver, Sander Pajusalu, Katrin Õunap, Sanna Puusepp, Paula Dobosz, Mateusz SypniewskiBirute Burnyte, Baiba Lace

Research output: Contribution to JournalArticleAcademicpeer-review


The investigated intronic CAPN3 variant NM_000070.3:c.1746-20C>G occurs in the Central and Eastern Europe with a frequency of >1% and there are conflicting interpretations on its pathogenicity. We collected data on 14 patients carrying the CAPN3 c.1746-20C>G variant in trans position with another CAPN3 pathogenic/likely pathogenic variant. The patients compound heterozygous for the CAPN3 c.1746-20C>G variant presented a phenotype consistent with calpainopathy of mild/medium severity. This variant is most frequent in the North/West regions of Russia and may originate from that area. Molecular studies revealed that different splicing isoforms are produced in the muscle. We hypothesize that c.1746-20C>G is a hypomorphic variant with a reduction of RNA and protein expression and only individuals having a higher ratio of abnormal isoforms are affected. Reclassification of the CAPN3 variant c.1746-20C>G from variant with a conflicting interpretation of pathogenicity to hypomorphic variant explains many unidentified cases of limb girdle muscular dystrophy R1 calpain 3-related in Eastern and Central Europe.
Original languageEnglish
JournalHuman mutation
Early online date2022
Publication statusE-pub ahead of print - 2022


  • CAPN3
  • LGMD
  • LGMD R1 calpain 3-related
  • calpainopathy
  • hypomorphic variant

Cite this