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LAMB3
laminin subunit beta 3
The LAMB3 gene provides instructions for the beta-3 subunit of laminin 332, a critical protein for maintaining the structural integrity and adhesion of skin and other tissues. LAMB3 encodes a component of laminin 332, a vital protein in the basement membrane of the skin.
LAMB3 is located on the long (q) arm of chromosome 1, at band 1q32.2. Arm ratio per GRCh38 - banding schematic.
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Overview
The LAMB3 gene, or laminin subunit beta 3, plays a key role in producing a specific subunit of laminin 332. This protein is fundamental to the formation and function of basement membranes, which are thin, supportive layers found in many tissues. Laminin 332 is particularly important in the skin, where it helps anchor the epidermis to underlying layers, contributing to its resilience and protective barrier function. Alterations in LAMB3 can compromise this essential structural support, leading to various inherited conditions.
What the gene does
The LAMB3 gene provides the genetic blueprint for the beta subunit of laminin 332, a heterotrimeric protein composed of alpha, beta, and gamma subunits. Laminins are a family of proteins that are integral to cell regulation, influencing cell growth, movement, and adhesion. They are also crucial for the assembly and organisation of basement membranes, which are specialised extracellular matrices separating different tissue layers. In the skin, laminin 332 is a major constituent of anchoring filaments, structures that connect the epidermal and dermal layers of the basement membrane, thereby securing the skin's integrity. Beyond its structural role, laminin 332 is implicated in wound healing processes, and research indicates potential functions in the cornea of the eye and in the development of tooth enamel.
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Chromosome location
The LAMB3 gene is situated on chromosome 1 at position 1q32.2. This specific genomic location indicates its address within the human genome, where it resides on the long arm of chromosome 1. The precise positioning of this gene is essential for understanding its genetic context and how variations within this region might impact its function.
Protein structure
The LAMB3 gene codes for a protein that is 1172 amino acids long (UniProt: Q13751). This protein exhibits a complex domain architecture, featuring several distinct regions. These include a Laminin N-terminal domain spanning amino acids 22-249, followed by multiple Laminin EGF-like domains: Laminin EGF-like 1 (amino acids 250-315), Laminin EGF-like 2 (amino acids 316-378), Laminin EGF-like 3 (amino acids 379-430), Laminin EGF-like 4 (amino acids 431-480), Laminin EGF-like 5 (amino acids 481-533), and Laminin EGF-like 6 (amino acids 534-580). Further domains include Domain II (amino acids 579-785), Domain alpha (amino acids 786-816), and Domain I (amino acids 817-1170). The protein also contains three coiled coil regions: one within Domain II (amino acids 723-757) and two within Domain I (amino acids 831-884 and 948-1133).
Key variants
Variants within the LAMB3 gene can affect the production or function of the beta-3 subunit of laminin 332. These genetic changes can range from single nucleotide alterations to larger deletions or insertions, and their impact depends on their location and effect on protein synthesis or structure. Pathogenic variants can disrupt the protein's ability to integrate into basement membranes, leading to compromised tissue integrity and function.
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.1357del | p.Cys453fs | Pathogenic/Likely pathogenic | ★★☆☆ | Junctional epidermolysis bullosa gravis of Herlitz |
c.1628dup | p.Cys546fs | Pathogenic | ★★☆☆ | Junctional epidermolysis bullosa, non-Herlitz type |
c.1696dup | p.Gln566fs | Pathogenic/Likely pathogenic | ★★☆☆ | Junctional epidermolysis bullosa |
c.1829G>A | p.Trp610Ter | Pathogenic | ★★☆☆ | Junctional epidermolysis bullosa |
c.2116del | p.Lys705_Ile706insTer | Pathogenic | ★★☆☆ | Junctional epidermolysis bullosa gravis of Herlitz |
c.2242G>T | p.Glu748Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Amelogenesis imperfecta type 1A |
c.2269G>T | p.Gly757Ter | Pathogenic | ★★☆☆ | Junctional epidermolysis bullosa |
c.2495del | p.Ala832fs | Pathogenic/Likely pathogenic | ★★☆☆ | Amelogenesis imperfecta type 1A |
c.2911_2938del | - | Pathogenic/Likely pathogenic | ★★☆☆ | Junctional epidermolysis bullosa gravis of Herlitz |
c.2983C>T | p.Gln995Ter | Pathogenic | ★★☆☆ | Junctional epidermolysis bullosa |
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
Pathogenic variants in the LAMB3 gene are associated with inherited conditions primarily affecting the skin. One such condition is Epidermolysis bullosa (junctional), which is an autosomal recessive disorder characterised by extreme skin fragility and blistering. More severe forms of this condition often arise from variants that prevent the production of functional laminin 332. LAMB3 variants are also linked to Amelogenesis imperfecta, a condition affecting the development of tooth enamel.
Inheritance pattern
Conditions caused by pathogenic LAMB3 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
The LAMB3 gene is part of several genetic testing panels within the UK's NHS Genomic Medicine Service. It is included in the green-rated PanelApp entries for Amelogenesis imperfecta (R340), Epidermolysis bullosa, and Epidermolysis bullosa and congenital skin fragility (R164). A 'green' rating signifies that there is strong evidence for the gene's association with these conditions, indicating its clinical utility in diagnosis.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the primary function of the LAMB3 gene?
The LAMB3 gene provides instructions for creating the beta-3 subunit of laminin 332. This protein is essential for forming basement membranes, particularly in the skin, where it helps anchor cells and provides structural support for tissue integrity and elasticity.
Which conditions are associated with LAMB3 gene variants?
Variants in the LAMB3 gene are primarily associated with inherited conditions like Epidermolysis bullosa (junctional), which causes severe skin blistering and fragility. They are also linked to Amelogenesis imperfecta, affecting tooth enamel development.
How is LAMB3 related to skin integrity?
LAMB3 encodes a crucial component of laminin 332, a protein found in the basement membrane beneath the skin's surface. Laminin 332 acts like an anchor, connecting the outer layer of skin (epidermis) to the underlying layers, giving skin its strength and resilience.
References
- Schneider H, Mühle C, Pacho F. Biological function of laminin-5 and pathogenic impact of its deficiency. European journal of cell biology. 2007. PMID: 17000025
- Hartwig B, Borm B, Schneider H. Laminin-5-deficient human keratinocytes: defective adhesion results in a saltatory and inefficient mode of migration. Experimental cell research. 2007. PMID: 17335805
- Varki R, Sadowski S, Pfendner E. Epidermolysis bullosa. I. Molecular genetics of the junctional and hemidesmosomal variants. Journal of medical genetics. 2006. PMID: 16473856
- Mühle C, Jiang QJ, Charlesworth A. Novel and recurrent mutations in the laminin-5 genes causing lethal junctional epidermolysis bullosa: molecular basis and clinical course of Herlitz disease. Human genetics. 2005. PMID: 15538630
- Aumailley M, Bruckner-Tuderman L, Carter WG. A simplified laminin nomenclature. Matrix biology : journal of the International Society for Matrix Biology. 2005. PMID: 15979864
- Nakano A, Chao SC, Pulkkinen L. Laminin 5 mutations in junctional epidermolysis bullosa: molecular basis of Herlitz vs. non-Herlitz phenotypes. Human genetics. 2002. PMID: 11810295
- Nakano A, Pfendner E, Hashimoto I. Herlitz junctional epidermolysis bullosa: novel and recurrent mutations in the LAMB3 gene and the population carrier frequency. The Journal of investigative dermatology. 2000. PMID: 11023379
- Pulkkinen L, Uitto J. Mutation analysis and molecular genetics of epidermolysis bullosa. Matrix biology : journal of the International Society for Matrix Biology. 1999. PMID: 10367729
- Pulkkinen L, Gerecke DR, Christiano AM. Cloning of the beta 3 chain gene (LAMB3) of human laminin 5, a candidate gene in junctional epidermolysis bullosa. Genomics. 1995. PMID: 7774918