Screening of calpain-3 autolytic activity in LGMD muscle: a functional map of CAPN3 gene mutations.
BACKGROUND
The diagnosis of calpainopathy is obtained by identifying calpain-3 protein deficiency or CAPN3 gene mutations. However, in many patients with limb girdle muscular dystrophy type 2A (LGMD2A), the calpain-3 protein quantity is normal because loss-of-function mutations cause its enzymatic inactivation. The identification of such patients is difficult unless a functional test suggests pursuing a search for mutations.


METHODS
A functional in vitro assay, which was able to test calpain-3 autolytic function, was used to screen a large series of muscle biopsy specimens from patients with unclassified LGMD/hyperCKaemia who have previously shown normal calpain-3 protein quantity.


RESULTS
Of 148 muscle biopsy specimens tested,17 samples (11%) had lost normal autolytic function. CAPN3 gene mutations were identified in 15 of 17 patients (88%), who account for about 20% of the total patients with LGMD2A diagnosed in our series.


CONCLUSIONS
The loss of calpain-3 autolytic activity is highly predictive of primary calpainopathy, and the use of this test as part of calpainopathy diagnosis would improve the rate of disease detection markedly. This study provides the first evidence of the pathogenetic effect of specific CAPN3 gene mutations on the corresponding protein function in LGMD2A muscle and offers new insights into the structural-functional relationship of the gene and protein regions that are crucial for the autolytic activity of calpain-3.
Fanin
M
M
Department of Neurosciences, University of Padova, Venetian Institute of Molecular Medicine, Padova, Italy. marina.fanin@unipd.it
Nascimbeni
A C
AC
Angelini
C
C
D017668:Age of Onset; D019943:Amino Acid Substitution; D001483:Base Sequence; D001706:Biopsy; D002154:Calpain / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D005091:Exons; D006801:Humans; D008958:Models, Molecular; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000473:pathology; D049288:Muscular Dystrophies, Limb-Girdle / Q000175:diagnosis* / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D020125:Mutation, Missense; D018807:Polymorphism, Single-Stranded Conformational; D017434:Protein Structure, Tertiary; D012189:Retrospective Studies
D009124:Muscle Proteins; C105884:CAPN3 protein, human; D002154:Calpain