Minicore Disease (Multicore Disease)

This is a relatively rare congenital myopathy with muscle biopsies showing multiple small randomly distributed areas in the muscle, with focal decrease in mitochondrial oxidative enzyme activity and focal myofibrillar degenerative change.

Clinically, patients present with hypotonia, delays in gross motor development, and nonprogressive sym­metric weakness of the trunk and proximal limb mus­culature. There may be mild facial weakness, ptosis, and ophthalmoplegia. There is also associated dia­phragmatic weakness, placing patients at risk for noc­turnal hypoventilation. Subtle ultrastructural changes allow this condition to be distinguished from central core disease. The cores are smaller in size (minicores) and not confined to the center of the fiber. Inheritance is usually autosomal-recessive, and two genes—the ryanodine receptor gene (RYR1), linked to chromo­some 19q13.1, and the selenoprotein N, 1 (SEPN1) gene, linked chromosome 1p35-p36, account for 50% of cases.