Overview
Cystathionine beta-synthase (CBS) deficiency leads to hyperhomocysteinemia due to impaired metabolism of homocysteine, often associated with metabolic derangements including dyslipidemia and potential pyridoxine responsiveness 12.Diagnosis
Elevated plasma homocysteine levels are primary indicators 1.
Pyridoxine responsiveness testing via high-dose pyridoxine challenge may be necessary to identify mild cases 1.
Genetic testing for CBS mutations confirms diagnosis 13.
Lipid profile abnormalities, particularly elevated triglycerides and cholesterol, can be observed 2.Management
First-line treatment: Pyridoxine supplementation for pyridoxine-responsive cases; dosing should be weight-based and duration-limited to avoid toxicity 1.
Adjunctive therapies: Vitamin B complex and betaine may help manage hyperhomocysteinemia and dyslipidemia 2.
Chemical chaperones: Consider use of compounds like ethanol, dimethyl sulfoxide, or trimethylamine-N-oxide to enhance mutant CBS enzyme function 3.Special Populations
Pediatrics: Pyridoxine challenge must be carefully managed due to risk of toxicity in neonates 1.
Comorbidities: Patients with dyslipidemia may benefit from additional lipid-lowering agents alongside homocysteine-lowering strategies 2.Key Recommendations
Implement weight-based dosing and duration guidelines for pyridoxine challenge in neonates to prevent toxicity (Evidence: Moderate 1).
Consider adjunctive therapies such as vitamin B complex and betaine to manage hyperhomocysteinemia and dyslipidemia in CBS deficiency (Evidence: Moderate 2).
Utilize chemical chaperones to potentially restore function in CBS mutant enzymes (Evidence: Weak 3).References
1 Ames EG, Scott AJ, Pappas KB, Moloney SM, Conway RL, Ahmad A. A cautionary tale of pyridoxine toxicity in cystathionine beta-synthase deficiency detected by two-tier newborn screening highlights the need for clear pyridoxine dosing guidelines. American journal of medical genetics. Part A 2020. link
2 Zhang T, Lu R, Chen Y, Yuan Y, Song S, Yan K et al.. Hyperhomocysteinemia and dyslipidemia in point mutation G307S of cystathionine β-synthase-deficient rabbit generated using CRISPR/Cas9. Lipids in health and disease 2020. link
3 Majtan T, Liu L, Carpenter JF, Kraus JP. Rescue of cystathionine beta-synthase (CBS) mutants with chemical chaperones: purification and characterization of eight CBS mutant enzymes. The Journal of biological chemistry 2010. link