[Sibling cases of severe infantile form of nemaline myopathy with ACTA1-gene mutation]

Severe infantile form of nemaline myopathy is clinically characterized by marked muscle hypotonia and weakness with respiratory and feeding difficulties since infancy. Recently, mutations in the skeletal muscle alpha-actine gene (ACTA1) have been identified in many patients with the nemaline myopathy. We experienced two cases of severe infantile form of nemaline myopathy with ACTA1 mutation (missence heterozygous mutation;c.553C>T, p.R185C) in siblings presenting with different clinical symptoms and courses. The elder brother was a typical "floppy infant" at birth. Because he could not suck and swallow at all, he was fed completely through a nasogastric tube. At 2 months of age, he developed respiratory insufficiency and was placed on a respirator all day. He was diagnosed with having nemaline myopathy from his muscle biopsy, which revealed marked variation in muscle fiber size with large numbers of nemaline bodies on Gomori-trichrome stain. In contrast, the younger brother presented with mild muscular hypotonia and feeding difficulty during the neonatal stage;therefore, he was partly fed through a nasogastric tube. At 2 months of age, he was admitted to our hospital because of respiratory distress, and he required nasal continuous positive airway pressure with oxygen followed by noninvasive positive pressure ventilation intermittently, mainly at night. He was followed at his home by parents with no serious problems;however he unexpectedly died at the age of 15 months. Although most cases of severe infantile form of nemaline myopathy caused by ACTA1 mutations are sporadic and have no family history, we emphasize that clinical symptoms are variable in siblings with the same mutation.