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B3GALT6
beta-1,3-galactosyltransferase 6
B3GALT6 is located on the short (p) arm of chromosome 1, at band 1p36.33. Arm ratio per GRCh38 - banding schematic.
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Overview
The B3GALT6 gene encodes beta-1,3-galactosyltransferase 6, an enzyme that plays a fundamental role in proteoglycan biosynthesis. Proteoglycans are large molecules consisting of a core protein with one or more glycosaminoglycan (GAG) chains attached. These structures provide mechanical support, regulate cell signalling, and maintain tissue architecture in connective tissues, cartilage, and bone. B3GALT6 catalyses the first committed step in assembling the GAG-protein linkage region, transferring galactose to a specific sugar acceptor. Without functional B3GALT6, proteoglycans cannot be properly assembled, leading to structural abnormalities in tissues that depend on these molecules for strength and flexibility.
What the gene does
Beta-1,3-galactosyltransferase 6 functions as a glycosyltransferase enzyme, catalysing the transfer of galactose from UDP-galactose to a xylose residue on serine residues of core proteins. This reaction represents the initial step in forming the tetrasaccharide linker region that connects glycosaminoglycan chains to proteoglycan core proteins. The enzyme is particularly important for the biosynthesis of heparan sulphate and chondroitin sulphate, two major types of GAG chains found abundantly in cartilage, bone, skin, and blood vessels. By establishing the linkage region, B3GALT6 enables subsequent enzymatic steps that elongate and modify GAG chains. The protein localises to the Golgi apparatus, where most glycosylation reactions occur. Proper B3GALT6 activity is essential for producing proteoglycans such as decorin, biglycan, and aggrecan, which contribute to the biomechanical properties of the extracellular matrix and regulate growth factor signalling during development and tissue repair.
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Chromosome location
The B3GALT6 gene is located on chromosome 1 at band p36.33, near the tip of the short arm. This chromosomal region contains numerous genes involved in early development and metabolic processes. The gene encodes a protein of 329 amino acids.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The beta-1,3-galactosyltransferase 6 protein contains a catalytic region typical of glycosyltransferase family members, with structural features that enable UDP-galactose binding and substrate recognition. The enzyme includes transmembrane segments that anchor it within the Golgi membrane, positioning the catalytic domain appropriately for interaction with acceptor substrates during proteoglycan assembly.
Key variants
Pathogenic variants in B3GALT6 are inherited in an autosomal recessive pattern, meaning affected individuals carry alterations in both gene copies. Loss-of-function variants that severely reduce or eliminate enzyme activity result in deficient proteoglycan synthesis. Missense variants affecting the catalytic region can impair galactose transfer efficiency, whilst nonsense and frameshift variants typically lead to absent or truncated proteins. The severity of clinical features often correlates with residual enzyme activity.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1A>G | p.Met1Val | Pathogenic/Likely pathogenic | ★★☆☆ | Spondyloepimetaphyseal dysplasia with joint laxity |
c.235A>G | p.Thr79Ala | Pathogenic | ★★☆☆ | Al-Gazali syndrome |
c.2T>C | p.Met1Thr | Pathogenic/Likely pathogenic | ★★☆☆ | B3GALT6-congenital disorder of glycosylation |
c.513_520del | p.Glu174fs | Pathogenic/Likely pathogenic | ★★☆☆ | Spondyloepimetaphyseal dysplasia with joint laxity |
c.556T>C | p.Phe186Leu | Pathogenic | ★★☆☆ | Spondyloepimetaphyseal dysplasia with joint laxity, type 1, with or without fractures |
c.766C>T | p.Arg256Trp | Pathogenic/Likely pathogenic | ★★☆☆ | Ehlers-Danlos syndrome, spondylodysplastic type, 2 |
c.925T>A | p.Ser309Thr | Pathogenic/Likely pathogenic | ★★☆☆ | Spondyloepimetaphyseal dysplasia with joint laxity |
g.(?_1167616)_(1170422_?)del | - | Pathogenic | ★☆☆☆ | Spondyloepimetaphyseal dysplasia with joint laxity, type 1, with or without fractures |
c.197_253del | p.Ala66_Arg84del | Pathogenic | ★☆☆☆ | Ehlers-Danlos syndrome, spondylodysplastic type, 2 |
c.1A>T | p.Met1Leu | Pathogenic | ★☆☆☆ | Fetal anomalies with a likely genetic cause |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Biallelic pathogenic variants in B3GALT6 cause Ehlers-Danlos syndrome (spondylodysplastic), a rare connective tissue disorder characterised by joint hypermobility, skin hyperextensibility, skeletal abnormalities, and short stature. Individuals with this condition typically present with progressive spinal deformities, osteopaenia, and joint dislocations due to deficient proteoglycan content in cartilage and bone. The disorder represents a congenital disorder of glycosylation affecting proteoglycan assembly. Clinical features vary in severity depending on the specific variants inherited and the degree of residual enzyme function.
Inheritance pattern
Conditions caused by pathogenic B3GALT6 variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
B3GALT6 appears on multiple NHS Genomic Medicine Service testing panels with green (high confidence) classification. These include the Congenital disorders of glycosylation panel, DDG2P, Ehlers Danlos syndrome with a likely monogenic cause (R101), Fetal anomalies (R21), Likely inborn error of metabolism (R98), Osteogenesis imperfecta (R102), Skeletal dysplasia (R104), and Undiagnosed metabolic disorders panels. Green classification indicates strong evidence supporting the gene-disease relationship, enabling its use in clinical diagnostic testing for individuals with relevant clinical presentations. Inclusion across skeletal and metabolic panels reflects the gene's role in both connective tissue integrity and glycosylation pathways.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What does the B3GALT6 gene do?
B3GALT6 provides instructions for making an enzyme that attaches galactose sugar molecules to proteins during proteoglycan synthesis. This process is essential for building the extracellular matrix that gives connective tissues their structural properties.
How are B3GALT6 variants inherited?
B3GALT6-related conditions follow an autosomal recessive inheritance pattern. This means an individual must inherit a pathogenic variant from both parents to develop the associated condition. Carriers with one variant typically do not show symptoms.
Can B3GALT6 variants be detected through carrier screening?
Yes, carrier screening can identify individuals who carry one pathogenic B3GALT6 variant. This information is particularly relevant for family planning, as two carriers have a 25% chance with each pregnancy of having a child affected by spondylodysplastic Ehlers-Danlos syndrome.