XYLT2 and osteoporosis: The 2023 Nosology distinguished between syndromes of OI (intrinsic bone fragility) and a large group of disorders with bone fragility resulting from heritable types of osteoporosis, singly or as a feature of a multi-trait heritable syndrome e.g. Spondylo-ocular syndrome resulting from genomic variants in XYLT2, On-Line Mendelian Inheritance in Man (OMIM): 605822 [4].