Multi-minicore disease--searching for boundaries: phenotype analysis of 38 cases

Multi-minicore disease (MmD) is a congenital myopathy morphologically defined by the presence of multiple small zones of sarcomeric disorganization and lack of oxidative activity ("minicores") in muscle fibers. The dinical expression of MmD is considered to be greatly variable, and the morphological lesions are nonspecific; therefore, its boundaries are poorly defined, and its molecular bases are not known. To better define the phenotypic characteristics of MmD, we analyzed a large series of 38 patients with multiple minicores in muscle fibers in the absence of any other potential cause. According to clinical features, 4 subgroups were identified. Most patients (30 cases) shared a common highly consistent phenotype marked by the axial predominance of muscle weakness and a high occurrence of severe respiratory insufficiency and scoliosis ("classical" form). Other forms were characterized by pharyngolaryngeal involvement and total lack of head control (2 cases), antenatal onset with arthrogryposis (3 cases), and slowly progressive weakness with marked hand amyotrophy (3 cases). Type 1 fiber predominance and hypotrophy as well as centrally located nuclei were found in every subgroup. MmD is thus phenotypically heterogeneous, but a typical recognizable phenotype does exist. This phenotype classification should be helpful when undertaking research into the molecular defects that cause MmD.