In this study, the HMDs found in the 119 enrolled patients included PMD, PMLD, HABC, GM1 and GM2 gangliosidosis, trichothiodystrophy, POL3R, HLD9, and 18q- syndrome (Table 2), of which POL3R and HLD9 were first diagnosed in China. The gene discussed is RARS1; the disease is Pelizeaus-Merzbacher spectrum disorder.