In mammals, there are three members in Phosphatidic acid preferring phospholipase A1 family all of which possess the DDHD domain: PA-PLA1/DDHD1, KIAA072p/DDHD2 and p125/Sec23ip; mutations in DDHD2 have been found in patients with the neurodegenerative disease Hereditary Spastic Paraplegia (Pensato et al., 2014; Nicita et al., 2019) and those in DDHD1 with Spastic Paraplegia 28 (SPG28) (Tesson et al., 2012). The gene discussed is SEC23IP; the disease is neurodegenerative disease.