XYLT2 and spondylo-ocular syndrome: Homozygous mutations in XYLT2 cause spondyloocular syndrome that is characterized by retinal detachment, amblyopia, nystagmus, hearing loss, heart septal defects, bone fragility, and mild learning difficulties (Table 1; Munns et al., 2015; Taylan et al., 2016, 2017; Umair et al., 2018).