Several LSDs (mucolipidosis types IV, IIIA [pseudo-Hurler polydystrophy], and II [I-cell disease], late infantile neuronal ceroid lipifuscinosis [CLN2], mucopolysaccharidosis VI, and GM1 gangliosidosis) also display mitochondrial abnormalities, including replacement of the extended tubular mitochondrial network with high numbers of relatively rounded depolarized mitochondria1. Here, TPP1 is linked to mucopolysaccharidosis type 6.