Core-like structures, with or without additional nemaline rods, have been reported in association with dominant mutations in the ACTA1 gene [73,74], and there is recent evidence that recessive mutations in the RYR1 gene may give rise to the appearance of centronuclear myopathy with or without additional cores on muscle biopsy [6]. The gene discussed is ACTA1; the disease is autosomal dominant centronuclear myopathy.