Cystathionine β‐synthase (CBS) Deficiency: Genetics


Cystathionine β‐synthase (CBS) is an enzyme that catalyses condensation of homocysteine and serine to cystathionine. CBS deficiency, an autosomal recessive trait with estimated population frequency of around 1:10 000–1:20 000, resembles in the most severe forms Marfan syndrome with thromboembolism and neurological impairment, whereas milder forms may manifest with only thromboembolism or may remain asymptomatic. Laboratory findings include grossly elevated plasma total homocysteine and in part of patients also elevated blood methionine; the latter feature is utilised in neonatal screening. CBS binds three cofactors: pyridoxal 5′‐phosphate, an allosteric activator S‐adenosylmethionine and haem with as yet unresolved function. In the CBS gene, more than 150 different mutations have been described to date, almost 90% of them are missense variants. Although some of the mutations affect ribonucleic acid processing and its stability, the majority of mutations lead to enzyme misfolding and misassembly, which may be in part rescued by chemical or molecular chaperones.

Key Concepts:

  • Cystathionine β‐synthase catalyses the first step in homocysteine trans‐sulfuration.

  • Cystathionine β‐synthase is a modular enzyme composed of a haem‐binding N‐terminal domain, the catalytically active core and the C‐terminal autoinhibitory domain.

  • More than 150 different pathogenic mutations have been described in the CBS gene, almost 90% of all mutant CBS alleles carry missense mutations.

  • Misfolding and misassembly of mutant CBS subunits is a common pathogenic mechanism leading to CBS deficiency.

  • Mutation topology predicts in part the behaviour of mutant CBS enzymes, solvent accessible mutations have less severe effect than those buried in the enzyme globule.

  • Deficient CBS activity leads to gross elevation of plasma total homocysteine and often to elevated blood methionine levels.

  • Phenotypic consequences of mutations in the CBS gene include thromboembolism and vascular occlusion, which is accompanied in some patients by lens dislocation, marfanoid features and varying degree of neurological involvement.

  • Population frequency of clinically ascertained patients with CBS deficiency is one to two orders of magnitude lower than the frequency calculated from the prevalence of heterozygotes for pathogenic mutations; this observation indicates an ascertainment bias or lack of symptoms in many CBS‐deficient individuals.

  • Murine models of CBS deficiency recapitulate in part the pathophysiology and organ involvement observed in human patients.

Keywords: homocysteine; homocystinuria; inborn errors of metabolism; cystathionine β‐synthase; mutations; pathogenesis; misfolding; chaperones; mouse models

Figure 1.

Metabolism of sulfur amino acids. A typical Western diet contains approximately 1–3 g of methionine (Met). Met reacts with adenosine triphosphate (ATP) to yield S‐adenosylmethionine (AdoMet), a reaction catalyzed by two methionine adenosyltransferases. AdoMet is utilised in numerous transmethylation reactions yielding S‐adenosylhomocysteine (AdoHcy). The latter compound is broken down by S‐adenosylhomocysteine hydrolase into adenosine and homocysteine (Hcy). Approximately half of the Hcy molecules are remethylated to methionine by betaine:homocysteine methyltransferase or by methionine synthase, which utilises methyltetrahydrofolate (CH3‐FH4) as the source of the methyl group. The other half of the Hcy moieties are converted to cysteine in the trans‐sulfuration pathway. The first step is the condensation of Hcy with serine (Ser) catalysed by cystathionine β‐synthase. Further steps of this pathway produce cysteine (Cys), glutathione (GSH) and taurine.

Figure 2.

Modular structure of the CBS enzyme. Each CBS subunit contains the N‐terminal haem‐binding domain, the conserved catalytic core with PLP‐binding lysine 119 and the autoinhibitory C‐terminal portion, which contains two so‐called CBS domains and which binds S‐adenosylmethionine. Reproduced, with permission, from Miles and Kraus (2004).

Figure 3.

Mutant CBS alleles: variability of mutations and ethnic distribution. An updated database of mutations in the CBS gene is maintained at the Krauslab Homepage (see Websites). The proportion and ethnic origin of ∼750 independent alleles were taken from this source.

Figure 4.

Expression of mutant CBS enzymes in Escherichia coli. (a) The series of 27 mutants was expressed in E. coli and further analysed for the presence of CBS antigen in nonparticulate water‐soluble fractions of bacterial extracts (Sup, supernatant) as well as in the sodium dodecyl sulfate (SDS)‐soluble particulate fraction (Pel, pellet) obtained by centrifugation using SDS‐polyacrylamide gel electrophoresis (PAGE) and Western blotting. The CBS antigen is present in all fractions of all mutants. (b) The quaternary structure of CBS mutants was assessed in the water‐soluble nonparticulate fraction of bacterial extracts by electrophoresis under native conditions followed by Western blotting; sharply demarcated fractions are tetramers and higher oligomers. These fractions are missing in some of the mutants indicating that they misfold and aggregate. (a) Mutant proteins expressed at 37°C. (b) Results of expression of mutant proteins at 18°C demonstrating increased formation of tetramers for several mutants. Solvent‐exposed mutations are mutations with accessible surface area larger than 40 Å2 and with relative accessible surface larger than 9%; buried mutations are the remaining mutations. pKK 388.1, extracts of bacteria transformed with the empty pKK 388.1 plasmid lacking any CBS; WT, bacterial extracts containing wild‐type CBS. Reproduced, with permission, from Kožich et al..

Figure 5.

Solvent exposure and misassembly of mutants. The individual data points show the correspondence between the amount of tetramer and activity of the mutants, which are both normalised to the amount and activity of wild‐type CBS that has been expressed in each series. Data are here combined separately for all solvent‐exposed (see panel a) and all buried mutations (see panel b); ○ and ▵ indicate data for expression at 37°C and 18°C, respectively. Linear regression analysis shows much stronger correlation between activity and the amount of tetramers for solvent‐exposed mutations than for the buried ones. Reproduced, with permission, from Kožich et al..



Akahoshi N, Kobayashi C, Ishizaki Y et al. (2008) Genetic background conversion ameliorates semi‐lethality and permits behavioral analyses in cystathionine beta‐synthase‐deficient mice, an animal model for hyperhomocysteinemia. Human Molecular Genetics 17(13): 1994–2005.

Bateman A (1997) The structure of a domain common to archaebacteria and the homocystinuria disease protein. Trends in Biochemical Sciences 22(1): 12–13.

Bruno S, Schiaretti F, Burkhard P et al. (2001) Functional properties of the active core of human cystathionine beta‐synthase crystals. Journal of Biological Chemistry 276(1): 16–19.

Chen X, Wang L, Fazlieva R and Kruger WD (2006) Contrasting behaviors of mutant cystathionine beta‐synthase enzymes associated with pyridoxine response. Human Mutation 27(5): 474–482.

Gan‐Schreier H, Kebbewar M, Fang‐Hoffmann J et al. (2010) Newborn population screening for classic homocystinuria by determination of total homocysteine from guthrie cards. Journal of Pediatrics 156(3): 427–432.

Gaustadnes M, Ingerslev J and Rutiger N (1999) Prevalence of congenital homocystinuria in Denmark. New England Journal of Medicine 340(19): 1513.

Gaustadnes M, Rudiger N, Rasmussen K and Ingerslev J (2000) Familial thrombophilia associated with homozygosity for the cystathionine beta‐synthase 833T→C mutation. Arteriosclerosis, Thrombosis, and Vascular Biology 20(5): 1392–1395.

Ge Y, Matherly LH and Taub JW (2001) Transcriptional regulation of cell‐specific expression of the human cystathionine beta‐synthase gene by differential binding of Sp1/Sp3 to the ‐1b promoter. Journal of Biological Chemistry 276(47): 43570–43579.

Gupta S, Kuhnisch J, Mustafa A et al. (2009) Mouse models of cystathionine beta‐synthase deficiency reveal significant threshold effects of hyperhomocysteinemia. FASEB Journal 23(3): 883–893.

Janosik M, Kery V, Gaustadnes M, Maclean KN and Kraus JP (2001a) Regulation of human cystathionine beta‐synthase by S‐adenosyl‐L‐methionine: evidence for two catalytically active conformations involving an autoinhibitory domain in the C‐terminal region. Biochemistry 40(35): 10625–10633.

Janosik M, Oliveriusova J, Janosikova B et al. (2001b) Impaired heme binding and aggregation of mutant cystathionine beta‐synthase subunits in homocystinuria. American Journal of Human Genetics 68(6): 1506–1513.

Janosik M, Sokolova J, Janosikova B et al. (2009) Birth prevalence of homocystinuria in Central Europe: frequency and pathogenicity of mutation c.1105C>T (p.R369C) in the cystathionine beta‐synthase gene. Journal of Pediatrics 154(3): 431–437.

Jhee KH, McPhie P and Miles EW (2000) Yeast cystathionine beta‐synthase is a pyridoxal phosphate enzyme but, unlike the human enzyme, is not a heme protein. Journal of Biological Chemistry 275(16): 11541–11544.

Jhee KH, Niks D, McPhie P, Dunn MF and Miles EW (2001) The reaction of yeast cystathionine beta‐synthase is rate‐limited by the conversion of aminoacrylate to cystathionine. Biochemistry 40(36): 10873–10880.

Kery V, Poneleit L, Meyer JD, Manning MC and Kraus JP (1999) Binding of pyridoxal 5′‐phosphate to the heme protein human cystathionine beta‐synthase. Biochemistry 38(9): 2716–2724.

Kopecka J, Krijt J, Rakova K and Kožich V (in press) Restoring assembly and activity of cystathionine beta‐synthase mutants by ligands and chemical chaperones. Journal of Inherited Metabolic Disease.

Kožich V and Kraus JP (1992) Screening for mutations by expressing patient cDNA segments in E. coli: homocystinuria due to cystathionine beta‐synthase deficiency. Human Mutation 1(2): 113–123.

Kožich V, Sokolova J, Klatovska V et al. (2010) Cystathionine beta‐synthase mutations: effect of mutation topology on folding and activity. Human Mutation 31(7): 809–819.

Maclean KN, Janosik M, Oliveriusova J, Kery V and Kraus JP (2000) Transsulfuration in Saccharomyces cerevisiae is not dependent on heme: purification and characterization of recombinant yeast cystathionine beta‐synthase. Journal of Inorganic Biochemistry 81(3): 161–171.

Maclean KN, Kraus E and Kraus JP (2004) The dominant role of Sp1 in regulating the cystathionine beta‐synthase ‐1a and ‐1b promoters facilitates potential tissue‐specific regulation by Kruppel‐like factors. Journal of Biological Chemistry 279(10): 8558–8566.

Maclean KN, Sikora J, Kožich V et al. (2010a) Cystathionine beta‐synthase null homocystinuric mice fail to exhibit altered hemostasis or lowering of plasma homocysteine in response to betaine treatment. Molecular Genetics and Metabolism 101(2–3): 163–171.

Maclean KN, Sikora J, Kožich V et al. (2010b) A novel transgenic mouse model of CBS‐deficient homocystinuria does not incur hepatic steatosis or fibrosis and exhibits a hypercoagulative phenotype that is ameliorated by betaine treatment. Molecular Genetics and Metabolism 101(2–3): 153–162.

Magner M, Krupkova L, Honzik T et al. (in press) Vascular presentation of cystathionine beta‐synthase deficiency in adulthood. Journal of Inherited Metabolic Disease.

Majors AK and Pyeritz RE (2000) A deficiency of cysteine impairs fibrillin‐1 deposition: implications for the pathogenesis of cystathionine beta‐synthase deficiency. Molecular Genetics and Metabolism 70(4): 252–260.

Majtan T, Liu L, Carpenter JF and Kraus JP (2010) Rescue of cystathionine beta‐synthase (CBS) mutants with chemical chaperones: purification and characterization of eight CBS mutant enzymes. Journal of Biological Chemistry 285(21): 15866–15873.

Majtan T, Singh LR, Wang L, Kruger WD and Kraus JP (2008) Active cystathionine beta‐synthase can be expressed in heme‐free systems in the presence of metal‐substituted porphyrins or a chemical chaperone. Journal of Biological Chemistry 283(50): 34588–34595.

Meier M, Janosik M, Kery V, Kraus JP and Burkhard P (2001) Structure of human cystathionine beta‐synthase: a unique pyridoxal 5′‐phosphate‐dependent heme protein. EMBO Journal 20(15): 3910–3916.

Mudd SH, Levy HL and Kraus JP (2001) Disorders of transsulfuration. In: Scriver CR, Beaudet AL, Sly WS and Valle D (eds) The Metabolic and Molecular Bases of Inherited Disease, 8th edn. vol. 2, pp. 2007–2056. New York: McGraw‐Hill.

Naughten ER, Yap S and Mayne PD (1998) Newborn screening for homocystinuria: Irish and world experience. European Journal of Pediatrics 157(suppl. 2): S84–S87.

Oliveriusova J, Kery V, Maclean KN and Kraus JP (2002) Deletion mutagenesis of human cystathionine beta‐synthase. Impact on activity, oligomeric status, and S‐adenosylmethionine regulation. Journal of Biological Chemistry 277(50): 48386–48394.

Pazicni S, Cherney MM, Lukat‐Rodgers GS et al. (2005) The heme of cystathionine beta‐synthase likely undergoes a thermally induced redox‐mediated ligand switch. Biochemistry 44(51): 16785–16795.

Ratnam S, Maclean KN, Jacobs RL et al. (2002) Hormonal regulation of cystathionine beta‐synthase expression in liver. Journal of Biological Chemistry 277(45): 42912–42918.

Refsum H, Fredriksen A, Meyer K, Ueland PM and Kase BF (2004) Birth prevalence of homocystinuria. Journal of Pediatrics 144(6): 830–832.

Robert K, Maurin N, Vayssettes C, Siauve N and Janel N (2005a) Cystathionine beta synthase deficiency affects mouse endochondral ossification. Anatomical Record. Part A, Discoveries in Molecular, Cellular, and Evolutionary Biology 282(1): 1–7.

Robert K, Nehme J, Bourdon E et al. (2005b) Cystathionine beta synthase deficiency promotes oxidative stress, fibrosis, and steatosis in mice liver. Gastroenterology 128(5): 1405–1415.

Scott JW, Hawley SA, Green KA et al. (2004) CBS domains form energy‐sensing modules whose binding of adenosine ligands is disrupted by disease mutations. Journal of Clinical Investigation 113(2): 274–284.

Selhub J and Miller JW (1992) The pathogenesis of homocysteinemia – interruption of the coordinate regulation by S‐adenosylmethionine of the remethylation and transsulfuration of homocysteine. American Journal of Clinical Nutrition 55(1): 131–138.

Shan X, Dunbrack RL Jr, Christopher SA and Kruger WD (2001) Mutations in the regulatory domain of cystathionine beta synthase can functionally suppress patient‐derived mutations in cis. Human Molecular Genetics 10(6): 635–643.

Shan X and Kruger WD (1998) Correction of disease‐causing CBS mutations in yeast. Nature Genetics 19: 91–93.

Singh LR, Chen X, Kožich V and Kruger WD (2007) Chemical chaperone rescue of mutant human cystathionine beta‐synthase. Molecular Genetics and Metabolism 91(4): 335–342.

Singh LR, Gupta S, Honig NH, Kraus JP and Kruger WD (2010) Activation of mutant enzyme function in vivo by proteasome inhibitors and treatments that induce Hsp70. PLoS Genetics 6(1): e1000807.

Skovby F, Gaustadnes M and Mudd SH (2010) A revisit to the natural history of homocystinuria due to cystathionine beta‐synthase deficiency. Molecular Genetics and Metabolism 99(1): 1–3.

Stabler SP, Steegborn C, Wahl MC et al. (2002) Elevated plasma total homocysteine in severe methionine adenosyltransferase I/III deficiency. Metabolism 51(8): 981–988.

Vadon‐Le Goff S, Delaforge M, Boucher JL et al. (2001) Coordination chemistry of the heme in cystathionine beta‐synthase: formation of iron(II)‐isonitrile complexes. Biochemical and Biophysical Research Communications 283(2): 487–492.

Vyletal P, Sokolova J, Cooper DN et al. (2007) Diversity of cystathionine beta‐synthase haplotypes bearing the most common homocystinuria mutation c.833T>C: a possible role for gene conversion. Human Mutation 28(3): 255–264.

Wang L, Chen X, Tang B et al. (2005) Expression of mutant human cystathionine beta‐synthase rescues neonatal lethality but not homocystinuria in a mouse model. Human Molecular Genetics 14(15): 2201–2208.

Wang L, Jhee KH, Hua X et al. (2004) Modulation of cystathionine beta‐synthase level regulates total serum homocysteine in mice. Circulation Research 94(10): 1318–1324.

Watanabe M, Osada J, Aratani Y et al. (1995) Mice deficient in cystathionine beta‐synthase: animal models for mild and severe homocyst(e)inemia. Proceedings of the National Academy of Sciences of the USA 92(5): 1585–1589.

Yap S, Boers GH, Wilcken B et al. (2001) Vascular outcome in patients with homocystinuria due to cystathionine beta‐synthase deficiency treated chronically: a multicenter observational study. Arteriosclerosis, Thrombosis, and Vascular Biology 21(12): 2080–2085.

Further Reading

Banerjee R and Zou CG (2005) Redox regulation and reaction mechanism of human cystathionine‐beta‐synthase: a PLP‐dependent hemesensor protein. Archives of Biochemistry and Biophysics 433(1): 144–156.

Carmel R and Jacobsen DW (2001) Homocysteine in Health and Disease. Cambridge, UK; New York: Cambridge University Press.

Kraus JP, Janosik M, Kožich V et al. (1999) Cystathionine beta‐synthase mutations in homocystinuria. Human Mutation 13(5): 362–375.

Kraus JP, Oliveriusova J, Sokalova J et al. (1998) The human cystathionine beta‐synthase (CBS) gene: complete sequence, alternative splicing, and polymorphisms. Genomics 52(3): 312–324.

Miles EW and Kraus JP (2004) Cystathionine beta‐synthase: structure, function, regulation, and location of homocystinuria‐causing mutations. Journal of Biological Chemistry 279(29): 29871–29874.

Mudd SH, Skovby F, Levy HL et al. (1985) The natural‐history of homocystinuria due to cystathionine beta‐synthase deficiency. American Journal of Human Genetics 37(1): 1–31.

Watson MS, Mann MY, Lloyd‐Puryear MA, Rinaldo P and Howell RR (2006) Newborn screening: toward a uniform screening panel and system. Genetics in Medicine 8(suppl. 1): 1S–252S.


CBS gene map

Coenzymes and catalysis

Cystathionine‐beta‐synthase (CBS); Locus ID: 875 LocusLink:

Homocystinuria due to cystathionine beta‐synthase deficiency; MIM number: 236200 OMIM:

Krauslab Homepage–University of Colorado Health Sciences Center

Map of all CBS mutations

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Kožich, Viktor, Kruger, Warren D, and Kraus, Jan Peter(Dec 2010) Cystathionine β‐synthase (CBS) Deficiency: Genetics. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0005935.pub2]