Dysferlin is the
protein product of the DYSF gene mapped at 2p31, which mutations cause
limb-girdle muscular dystrophy type 2B (
LGMD2B) and
Miyoshi myopathy. To date, nine autosomal recessive forms (AR-LGMD) have been identified: four genes, which code for the
sarcoglycan glycoproteins, are associated with both mild and severe forms, the
sarcoglycanopathies (
LGMD2C, 2D, 2E and 2F). The other five forms, usually causing a milder phenotype are
LGMD2A (
calpain 3),
LGMD2B (
dysferlin),
LGMD2G (telethonin),
LGMD2H (9q31-11), and LGMD21 (19q13.3). We studied
dysferlin expression in a total of 176 patients, from 166 LGMD families: 12
LGMD2B patients, 70 with other known forms of
muscular dystrophies (
LGMD2A,
sarcoglycanopathies,
LGMD2G), in an attempt to assess the effect of the primary gene-product deficiency on
dysferlin. In addition, 94 still unclassified LGMD families were screened for
dysferlin deficiency. In eight
LGMD2B patients from five families, no
dysferlin was observed in muscle biopsies, both through immunofluorescence (IF) and Western blot methodologies, while in two families, a very faint band was detected. Both patterns, negative or very faint bands, were concordant in patients belonging to the same families, suggesting that
dysferlin deficiency is specific to
LGMD2B. Myoferlin, the newly identified homologue of
dysferlin was studied for the first time in
LGMD2B patients. Since no difference was observed between patients mildly and severely affected, this
protein do not seem to modify the phenotype in the present
dysferlin-deficient patients.
Dystrophin,
sarcoglycans, and telethonin were normal in all
LGMD2B patients, while patients with
sarcoglycanopathies (2C, 2D, and 2E),
LGMD2A,
LGMD2G, and DMD showed the presence of a normal
dysferlin band by Western blot and a positive pattern on IF. These data suggest that there is no interaction between
dysferlin and these
proteins. However,
calpain analysis showed a weaker band in four patients from two families with intra-familial concordance. Therefore, this secondary deficiency of
calpain in
LGMD2B families, may indicate an interaction between
dysferlin and
calpain in muscle.
Dysferlin was also present in cultured myotubes, in chorionic villus, and in the skin.
Dysferlin deficiency was found in 24 out of a total of 166 Brazilian AR-LGMD families screened for
muscle proteins (approximately 14%), thus representing the second most frequent known LGMD form, after
calpainopathy, in our population.