SMPD1 and hyperinsulinemic hypoglycemia, familial, 4: Excess SM that occurs in SMPD1 (sphingomyelin phosphodiesterase 1, acid lysosomal)-deficiency (Niemann-Pick diseases) prevents autophagosome closure by defective regulation of ATG9 (autophagy related 9) cycling during autophagosome maturation [51].