Possible explanations include the selective expression of a DNAJB6 client protein in skeletal muscle, the interaction of DNAJB6 with the CASA system particularly with BAG3 (already known to cause a myofibrillar myopathy), or a functional redundancy of DNAJ family members in all tissues except skeletal muscle. The gene discussed is CSN1S1; the disease is myofibrillar myopathy.