Autosomal Dominant Limb-Girdle Muscular Dystrophies

Abstract

The autosomal dominant limb-girdle muscular dystrophies (LGMD-D) are a genetically heterogeneous group of myopathies presenting with progressive proximal weakness. LGMD-D1 is caused by variants in DNAJB6 and may represent an under-recognized disorder with significant clinical variability, including early onset and distal-predominant weakness. LGMD-D2 is much rarer and is caused by variants in TNPO3. Both LGMD-D1 and LGMD-D2 can show features of myofibrillar myopathy on muscle biopsy. LGMD-D3 is characterized by the distinctive clinical feature of finger flexor involvement. The disease is caused by variants in HNRNPDL and shares histological and pathophysiological features with vacuolar myopathies and multisystem proteinopathies caused by variants in other heterogeneous nuclear ribonucleoproteins. LGMD-D4 is a recently recognized dominant calpainopathy, which features later onset and milder symptoms than its recessive counterpart. The recent recognition of this disorder brings additional complexity to the evaluation of patients with single variants in CAPN3. The last of the currently recognized dominant LGMDs is LGMD-D5, caused by variants in the collagen VI genes. Collagenopathies can present with a broad spectrum of phenotype severity and feature cutaneous findings, contractures, and hyperlaxity. This chapter also discusses caveolinopathy (formerly LGMD1C), a dominantly inherited muscular dystrophy caused by variants in CAV3. Defects in caveolin-3 lead to a range of muscular phenotypes: proximal myopathy, distal myopathy, rippling muscle disease, rhabdomyolysis and asymptomatic hyperCKemia.