To assess the relevance of these findings to patients with AP-4 deficiency syndrome, we examined the distribution of ATG9A in skin fibroblasts from one control individual and two patients with homozygous, inactivating mutations in the AP4M1 gene encoding the μ4 subunit of AP-4 [7] (Fig 4). The gene discussed is AP4M1; the disease is alkaline phosphatase measurement.