Biallelic loss-of-function mutations in MYPN have recently been identified in patients with nemaline myopathy (Miyatake et al., 2017), cap myopathy (Lornage et al., 2017), and congenital myopathy with hanging big toe (Merlini et al., 2019), some of which had mild cardiac involvement. Here, MYPN is linked to cap myopathy.