Gene replacement therapy for muscular dystrophy

Disclosed is a method for treating a patient suffering from the disease sarcoglycan-deficient limb-girdle muscular dystrophy by gene replacement therapy. Sarcoglycan gene replacement therapy produces extensive long-term expression of the sarcoglycan species which restores the entire sarcoglycan complex, results in the stable association of alphα-dystroglycan with the sarcolemma, and eliminates the morphological markers of limb-girdle muscular dystrophy. In another aspect, the invention relates to a method for determining a specific defective sarcoglycan species in the tissue of a patient. The method involves culture of muscle cells obtained from the patient, and the independent introduction of expression vectors encoding each of the sarcoglycan species, α, β, γ, and δ, into the cultured cells with subsequent assaying for restoration of the dystrophin-glycoprotein complex. In another aspect, the invention relates to a mouse, and cells derived therefrom, homozygous for a disrupted α-sarcoglycan gene. The disruption prevents the synthesis of functional α-sarcoglycan in cells of the mouse and results in the mutant mouse having no detectable sarcospan, β-, γ-, δ-sarcoglycan, and reduced α-dystroglycan in the sarcolemma of skeletal and cardiac muscles, and a reduction of dystrophin in skeletal muscle, when compared to tissue of a mouse lacking a disrupted α-sarcoglycan gene. In another aspect, the invention relates to methods for screening for therapeutic agents useful in the treatment of sarcoglycan-deficient limb-girdle muscular dystrophy. The methods involve administering a candidate therapeutic agent to a mouse, or cells derived therefrom, and assaying for therapeutic effects on the mouse or cells, with the determination of therapeutic effects being a reduction or reversal in disease progression, or a restoration of the dystroglycan complex.