In 2000, a pathogenic TNNT1 founder variant characterized by a stop codon in exon 11 was identified in the North American Amish community, associated with a form of congenital myopathy named nemaline myopathy (NM) type 5 (NEM5, MIM 605355) on muscle biopsy (Johnston et al., 2000). Here, TNNT1 is linked to congenital myopathy with cores.