In conjunction, these data supported the occurrence of paternal UPD for chromosome 1 as the source of simultaneous homozygous mutations in ABCA4 and USH2A. Various instances of recessive diseases associated with paternally derived UPD for chromosome 1 have been demonstrated, including infantile hypophosphatasia (ALPl gene) (Watanabe et al., 2014), neuronal ceroid lipofuscinosis-1 (PPT1) (Nilda et al., 2016; Travaglini et al., 2017), and atypical Hutchinson–Gilford progeria syndrome (ZMPSTE24) (Cassini et al., 2018) among others (Zeng et al., 2006; Miura et al., 2000; Manoli et al., 2010). Here, PPT1 is linked to hypophosphatasia.