Insights in the etiopathology of galactosyltransferase {II} (GalT-II) deficiency from transcriptome-wide expression profiling of skin fibroblasts of two sisters with compound heterozygosity for two novel {B3GALT6} mutations

摘要

Abstract Mutations in B3GALT6, encoding the galactosyltransferase {II} (GalT-II) involved in the synthesis of the glycosaminoglycan (GAG) linkage region of proteoglycans (PGs), have recently been associated with a spectrum of connective tissue disorders, including spondyloepimetaphyseal dysplasia with joint laxity type 1 (SEMDJL1) and Ehlers–Danlos-like syndrome. Here, we report on two sisters compound heterozygous for two novel {B3GALT6} mutations that presented with severe short stature and progressive kyphoscoliosis, joint hypermobility and laxity, hyperextensible skin, platyspondyly, short ilia, and elbow malalignment. Microarray-based transcriptome analysis revealed the differential expression of several genes encoding extracellular matrix (ECM) structural components, including COMP, SPP1, COL5A1, and COL15A1, enzymes involved in {GAG} synthesis and in {ECM} remodeling, such as CSGALNACT1, CHPF, LOXL3, and STEAP4, signaling transduction molecules of the TGFβ/BMP pathway, i.e., GDF6, GDF15, and BMPER, and transcription factors of the {HOX} and {LIM} families implicated in skeletal and limb development. Immunofluorescence analyses confirmed the down-regulated expression of some of these genes, in particular of the cartilage oligomeric matrix protein and osteopontin, encoded by {COMP} and SPP1, respectively, and showed the predominant reduction and disassembly of the heparan sulfate specific GAGs, as well as of the {PG} perlecan and type {III} and V collagens. The key role of GalT-II in {GAG} synthesis and the crucial biological functions of {PGs} are consistent with the perturbation of many physiological functions that are critical for the correct architecture and homeostasis of various connective tissues, including skin, bone, cartilage, tendons, and ligaments, and generates the wide phenotypic spectrum of GalT-II-deficient patients.