Cystathionine β-synthase (CBS) deficiency (classical homocystinuria) has a wide range of severity. Mildly affected patients typically present as adults with thromboembolism and respond to treatment with pyridoxine. Severely affected patients usually present during childhood with learning difficulties, ectopia lentis and skeletal abnormalities; they are pyridoxine non-responders (NR) or partial responders (PR) and require treatment with a low-methionine diet and/or betaine. The European network and registry for Homocystinurias and methylation Defects (E-HOD) has published management guidelines for CBS deficiency and recommended keeping plasma total homocysteine (tHcy) concentrations below 100 μmol/L. We have now analysed data from 311 patients in the registry to see how closely treatment follows the guidelines. Pyridoxine-responsive patients generally achieved tHcy concentrations below 50 μmol/L, but many NRs and PRs had a mean tHcy considerably above 100 μmol/L. Most NRs were managed with betaine and a special diet. This usually involved severe protein restriction and a methionine-free amino acid mixture, but some patients had a natural protein intake substantially above the WHO safe minimum. Work is needed on the methionine content of dietary protein as estimates vary widely. Contrary to the guidelines, most NRs were on pyridoxine, sometimes at dangerously high doses. tHcy concentrations were similar in groups prescribed high or low betaine doses and natural protein intakes. High tHcy levels were probably often due to poor compliance. Comparing time-to-event graphs for NR patients detected by newborn screening and those ascertained clinically showed that treatment could prevent thromboembolism (risk ratio 0.073) and lens dislocation (risk ratio 0.069).

• Keywords
• betaine, homocystinuria, methionine, newborn screening, protein restriction, pyridoxine,
• MeSH
• Betaine therapeutic use   MeSH
• Cystathionine beta-Synthase * deficiency   genetics   MeSH
• Child MeSH
• Adult MeSH
• Homocysteine blood   MeSH
• Homocystinuria * diet therapy   drug therapy   diagnosis   blood   MeSH
• Infant MeSH
• Humans MeSH
• Methionine MeSH
• Adolescent MeSH
• Young Adult MeSH
• Infant, Newborn MeSH
• Child, Preschool MeSH
• Pyridoxine * therapeutic use   MeSH
• Registries MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Infant MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Infant, Newborn MeSH
• Child, Preschool MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Betaine MeSH
• Cystathionine beta-Synthase * MeSH
• Homocysteine MeSH
• Methionine MeSH
• Pyridoxine * MeSH

Cystathionine beta-synthase (CBS)-deficient homocystinuria (HCU) is the most common inborn error of sulfur amino acid metabolism. The pyridoxine non-responsive form of the disease manifests itself by massively increasing plasma and tissue concentrations of homocysteine, a toxic intermediate of methionine metabolism that is thought to be the major cause of clinical complications including skeletal deformities, connective tissue defects, thromboembolism and cognitive impairment. The current standard of care involves significant dietary interventions that, despite being effective, often adversely affect quality of life of HCU patients, leading to poor adherence to therapy and inadequate biochemical control with clinical complications. In recent years, the unmet need for better therapeutic options has resulted in development of novel enzyme and gene therapies and exploration of pharmacological approaches to rescue CBS folding defects caused by missense pathogenic mutations. Here, we review scientific evidence and current state of affairs in development of recent approaches to treat HCU.

• Keywords
• chaperones, cystathionine beta-synthase, enzyme therapy, gene therapy, homocystinuria, pegtibatinase, proteasome inhibitors,
• MeSH
• Cystathionine beta-Synthase genetics   metabolism   MeSH
• Homocystinuria * drug therapy   genetics   metabolism   MeSH
• Quality of Life MeSH
• Humans MeSH
• Mutation, Missense MeSH
• Thromboembolism * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Cystathionine beta-Synthase MeSH