The LBR gene provides instructions for making a protein called the lamin B receptor. Different regions (domains) of this protein give it two distinct functions.
One region of the protein, called the sterol reductase domain, gives the protein sterol reductase function (specifically Δ14-sterol reductase function). This function of the lamin B receptor plays an important role in the production (synthesis) of cholesterol. Cholesterol is a lipid (fat) that is obtained from foods that come from animals: eggs, meat, fish, and dairy products. The body also makes (synthesizes) its own cholesterol. During cholesterol synthesis, the sterol reductase function of the lamin B receptor allows the protein to perform one of several chemical reactions that convert a molecule called lanosterol to cholesterol.
The body needs cholesterol to develop and function normally. Before birth, cholesterol interacts with signaling proteins that control early development of the brain, limbs, genitals, and other structures. It is also an important component of cell membranes and myelin, the fatty covering that insulates nerve cells. Additionally, cholesterol is used to make certain hormones and is important for the production of acids used in digestion (bile acids).
Another region of the lamin B receptor, called the DNA-binding domain, attaches (binds) to chromatin, the complex of DNA and proteins that packages DNA into chromosomes. The lamin B receptor can be found in the membrane that surrounds the nucleus (the nuclear envelope). The protein's interaction with chromatin attaches it to the nuclear envelope and helps maintain the chromatin's structure. Proper interaction of chromatin with the nuclear envelope may play a role in several important cellular functions such as making new copies of DNA (replication), controlling the activity of genes, and regulating programmed cell death (apoptosis). The DNA-binding domain of the protein also plays a role in the formation of the nucleus within cells.
Health Conditions Related to Genetic Changes
Several mutations in the LBR gene have been found to cause Greenberg dysplasia. This severe condition is characterized by abnormal bone formation and is fatal before birth. Research suggests that this condition is caused by the loss of the sterol reductase function of the lamin B receptor. Some LBR gene mutations that cause Greenberg dysplasia change single protein building blocks (amino acids) in the sterol reductase domain of the lamin B receptor, which leads to the loss of sterol reductase activity. Other mutations lead to an abnormally short protein that is likely nonfunctional.
Loss of the sterol reductase function of the lamin B receptor disrupts the normal synthesis of cholesterol within cells. Absence of this function may also allow potentially toxic byproducts of cholesterol synthesis to build up in the body's tissues. Researchers suspect that low cholesterol levels or an accumulation of other substances disrupts the growth and development of many parts of the body. It is not known, however, how a disturbance of cholesterol synthesis leads to the specific features of Greenberg dysplasia.More About This Health Condition
Mutations in the LBR gene can also cause Pelger-Huët anomaly, a condition that affects the shape of the nucleus and the structure of chromatin in certain cells but causes no outward signs or symptoms. The nuclei of blood cells called granulocytes normally have multiple segments (or lobes). In contrast, the nuclei of granulocytes in people with Pelger-Huët anomaly have fewer segments than normal (they are hypolobulated). In addition, the chromatin in affected cells appears coarser than usual when viewed under a microscope.
Mutations that cause Pelger-Huët anomaly usually lead to an abnormally short lamin B receptor and reduce the amount of functional protein. It is thought that impairment of the receptor's DNA-binding domain leads to this condition.
Other Names for This Gene
- integral nuclear envelope inner membrane protein
- lamin-B receptor
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
- Clayton P, Fischer B, Mann A, Mansour S, Rossier E, Veen M, Lang C, Baasanjav S, Kieslich M, Brossuleit K, Gravemann S, Schnipper N, Karbasyian M, Demuth I, Zwerger M, Vaya A, Utermann G, Mundlos S, Stricker S, Sperling K, Hoffmann K. Mutations causing Greenberg dysplasia but not Pelger anomaly uncouple enzymatic from structural functions of a nuclear membrane protein. Nucleus. 2010 Jul-Aug;1(4):354-66. doi: 10.4161/nucl.1.4.12435. Epub 2010 May 21. Citation on PubMed or Free article on PubMed Central
- Duband-Goulet I, Courvalin JC. Inner nuclear membrane protein LBR preferentially interacts with DNA secondary structures and nucleosomal linker. Biochemistry. 2000 May 30;39(21):6483-8. Citation on PubMed
- Hoffmann K, Dreger CK, Olins AL, Olins DE, Shultz LD, Lucke B, Karl H, Kaps R, Müller D, Vayá A, Aznar J, Ware RE, Sotelo Cruz N, Lindner TH, Herrmann H, Reis A, Sperling K. Mutations in the gene encoding the lamin B receptor produce an altered nuclear morphology in granulocytes (Pelger-Huët anomaly). Nat Genet. 2002 Aug;31(4):410-4. Epub 2002 Jul 15. Citation on PubMed
- Oosterwijk JC, Mansour S, van Noort G, Waterham HR, Hall CM, Hennekam RC. Congenital abnormalities reported in Pelger-Huët homozygosity as compared to Greenberg/HEM dysplasia: highly variable expression of allelic phenotypes. J Med Genet. 2003 Dec;40(12):937-41. Review. Citation on PubMed or Free article on PubMed Central
- Silve S, Dupuy PH, Ferrara P, Loison G. Human lamin B receptor exhibits sterol C14-reductase activity in Saccharomyces cerevisiae. Biochim Biophys Acta. 1998 Jun 15;1392(2-3):233-44. Citation on PubMed
- Tseng LC, Chen RH. Temporal control of nuclear envelope assembly by phosphorylation of lamin B receptor. Mol Biol Cell. 2011 Sep;22(18):3306-17. doi: 10.1091/mbc.E11-03-0199. Epub 2011 Jul 27. Citation on PubMed or Free article on PubMed Central
- Waterham HR, Koster J, Mooyer P, Noort Gv Gv, Kelley RI, Wilcox WR, Wanders RJ, Hennekam RC, Oosterwijk JC. Autosomal recessive HEM/Greenberg skeletal dysplasia is caused by 3 beta-hydroxysterol delta 14-reductase deficiency due to mutations in the lamin B receptor gene. Am J Hum Genet. 2003 Apr;72(4):1013-7. Epub 2003 Feb 28. Citation on PubMed or Free article on PubMed Central