BGN and Meester-Loeys syndrome: Specific hemizygous missense variants in the X-linked BGN gene, encoding the extracellular matrix protein biglycan, cause spondyloepimetaphyseal dysplasia (SEMD, biglycan type) (Cho et al., 2016), while loss-of-function pathogenic variants in this gene have been linked to an aortopathy syndrome called Meester-Loeys Syndrome (Meester et al., 2017).