The HEXB gene (Hexosaminidase Subunit Beta) is located on chromosome 5q13.3 and encodes the beta subunit of β-hexosaminidase, a lysosomal hydrolase essential for catabolism of GM2 ganglioside and other N-acetylhexosamine-containing compounds. Mutations in HEXB cause Sandhoff disease, a severe lysosomal storage disorder similar to Tay-Sachs but with additional accumulation of globotriaosylceramide (Gb3)[1].
| Property | Value |
|---|---|
| Gene Symbol | HEXB |
| Full Name | Hexosaminidase Subunit Beta |
| Chromosomal Location | 5q13.3 |
| NCBI Gene ID | 3074 |
| OMIM ID | 272800 |
| Ensembl ID | ENSG00000213626 |
| UniProt ID | P07604 |
| Protein Length | 529 amino acids |
| Molecular Weight | 58.8 kDa |
| Protein Class | Lysosomal hydrolase, glycosidase |
The HEXB gene encodes the beta subunit of β-hexosaminidase, a lysosomal hydrolase critical for degrading glycolipids, glycoproteins, and glycosaminoglycans. The beta subunit partners with the alpha subunit (from HEXA) to form hexosaminidase A (Hex A), or pairs with another beta subunit to form hexosaminidase B (Hex B)[2]:
| Enzyme | Subunits | Substrate Specificity | Clinical Relevance |
|---|---|---|---|
| Hex A | α + β | GM2 ganglioside, GAGs, glycoproteins | Critical for CNS |
| Hex B | β + β | Glycolipids, GAGs (not GM2) | Sandhoff disease |
| Hex S | α + α | Usually inactive | Rare variant |
HEXB produces the beta subunit which:
HEXB is expressed in most tissues with highest activity in:
| Tissue | Expression Level | Notes |
|---|---|---|
| Brain | High | Neurons, glia essential for function |
| Liver | High | Hepatocytes, sinusoidal cells |
| Kidney | High | Proximal tubules |
| Spleen | Moderate | Immune cells |
| Fibroblasts | Moderate | Cultured cells for diagnosis |
| Region | Expression | Significance |
|---|---|---|
| Cerebellum | High | Purkinje cells vulnerable |
| Cortex | Moderate-High | Pyramidal neurons |
| Hippocampus | Moderate | CA regions |
| Basal ganglia | Moderate | Motor control |
| White matter | Moderate | Oligodendrocytes |
Sandhoff disease is an autosomal recessive neurodegenerative disorder caused by HEXB mutations resulting in deficient Hex A AND Hex B activity. Unlike Tay-Sachs (HEXA), HEXB deficiency affects both enzymes[3]:
| Form | Onset | Progression | Life Expectancy |
|---|---|---|---|
| Infantile | 3-6 months | Rapid | 2-4 years |
| Juvenile | 2-5 years | Slower | 10-15 years |
| Adult (LADB) | Adolescence/adulthood | Very slow | Variable |
| Feature | Description |
|---|---|
| Neurodegeneration | Progressive motor/cognitive decline |
| Cherry-red macula | Classic ophthalmologic finding |
| Hepatosplenomegaly | More prominent than Tay-Sachs |
| Hypotonia | Early motor weakness |
| Seizures | Common in infantile form |
| Startle response | Hyperacoustic |
HEXB variants have been implicated in Parkinson's disease[4]:
| Association | Evidence |
|---|---|
| Lysosomal dysfunction | HEXB variants affect autophagy |
| Alpha-synuclein | GBA/HEXB interactions studied |
| GWAS signals | Some association studies |
| LRRK2 interaction | Possible mechanistic link |
While not a primary cause, HEXB may play a role in AD[5]:
| Mutation Type | Common Variants | Effect |
|---|---|---|
| Missense | R505H, G476R | Reduced activity |
| Nonsense | W474X, Q80X | Truncated protein |
| Splice site | IVS5+1G>A | Exon skipping |
| Large deletion | Exon 5-8 del | Null allele |
| Genotype | Phenotype |
|---|---|
| Two null alleles | Severe infantile |
| One null + one missense | Juvenile form |
| Two missense (residual activity) | Adult form |
| Approach | Strategy | Status | Challenges |
|---|---|---|---|
| Gene therapy | AAV-HEXB to CNS | Preclinical | Delivery, expression |
| Enzyme replacement | Recombinant Hex A/B | Experimental | BBB penetration |
| Substrate reduction | Reduce ganglioside synthesis | Research | Efficacy |
| Chaperone therapy | Enhance residual activity | Research | Specificity |
| Agent | Mechanism | Status |
|---|---|---|
| Migalastat derivatives | Pharmacological chaperone | Research |
| Lucerastat | Oral substrate reduction | Clinical trials |
| Eliglustat | GCS inhibitor | Investigational |
| Method | Application |
|---|---|
| Enzyme assay | Plasma, leukocytes, fibroblasts |
| Genetic testing | Mutation analysis |
| Prenatal testing | Chorionic villus, amniocentesis |
| Newborn screening | Pilot programs in some states |
| Model | Description | Research Use |
|---|---|---|
| Hexb−/− mice | Knockout, Sandhoff phenotype | Disease mechanism |
| Hexb−/− cats | Naturally occurring | Therapy testing |
| Hexb−/− dogs | Naturally occurring | Preclinical |
HEXB encodes the beta subunit of β-hexosaminidase, an essential lysosomal enzyme for catabolizing GM2 ganglioside. Mutations cause Sandhoff disease, a severe neurodegenerative disorder characterized by GM2 accumulation in neurons. Beyond this rare disease, HEXB variants may contribute to Parkinson's disease risk through lysosomal dysfunction mechanisms. Therapeutic approaches including gene therapy, substrate reduction, and enzyme enhancement are under active development.
HEXB (Beta-Hexosaminidase B) expression patterns in the human brain:
HEXB is expressed in:
| Region | Expression Level | Data Source |
|---|---|---|
| Substantia Nigra | Moderate | Human MTG |
| Cerebral Cortex | Moderate-High | Allen Human Brain Atlas |
| Hippocampus | Moderate-High | Allen Human Brain Atlas |
| Striatum | Moderate | Human MTG |
HEXB is essential for GM2 ganglioside degradation. Mutations cause Sandhoff disease, a lysosomal storage disorder with neurodegenerative phenotype.
Neote K, et al. Structure and function of the HEXB gene encoding the beta-subunit of human beta-hexosaminidase B. Journal of Biological Chemistry. 1988. ↩︎
Sandhoff K, et al. The GM2 gangliosidoses and their gene defects. Annals of the New York Academy of Sciences. 1998. ↩︎
Strømme P, et al. Sandhoff disease: identification of the disease-causing mutation and prenatal diagnosis. Journal of Inherited Metabolic Disease. 1992. ↩︎
Solovyeva N, et al. HEXB variants in Parkinson's disease. Mov Disord. 2018. ↩︎
Beyer BA, et al. Hexosaminidase activity as a biomarker in neurodegenerative disease. Nat Rev Neurol. 2022. ↩︎
Cachón-González MB, et al. Effective gene therapy in an authentic model of Tay-Sachs-related diseases. Proceedings of the National Academy of Sciences. 2006. ↩︎
Ma L, et al. GM2 gangliosidosis: mechanism and therapies. J Clin Invest. 2020. ↩︎