Objectives
To examine the expression of laminin 2 subunits in skeletal muscle in patients with LGMD and to define the clinical features of patients with LGMD who have abnormal expression of laminin 2 subunits.

Methods
We studied muscle biopsy specimens from 18 patients with LGMD using immunofluorescence with antibodies against dystrophin C-terminus, β-dystroglycan, -sarcoglycan, -sarcoglycan, and the laminin subunits merosin, β₁, and ₁. Of the 18 biopsy specimens, 9 were available for electron microscopic examination of the muscle basement membrane. The clinical features associated with abnormal laminin β₁ chain immunoreactivity were further described.

Results
Laminin β₁ chain was either barely detectable or severely reduced in 3 cases of patients with LGMD in which the biopsy specimens showed normal staining with the other antibodies. Patients in all 3 cases had common clinical features consistent with a slowly progressive, adultonset LGMD. Specimens from 2 of the 3 cases that were available for ultrastructural examination showed significant abnormalities of the muscle fiber basement membrane.

Conclusions
Abnormal expression of laminin β₁ chain without concomitant deficiency of -sarcoglycan in skeletal muscle has not been previously described in LGMD. Reduced laminin β₁ chain immunoreactivity may potentially serve as a marker for defining subsets of individuals with LGMD, in particular those with slowly progressive, adult-onset pelvifemoral presentation. The abnormality of muscle fiber basement membranes in specimens from cases that were available for ultrastructural study suggests that defects in the extracellular matrix may play a role in the pathogenesis of this subset of LGMD.