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A rationale for cystine supplementation in severe homocystinuria

P J Lee1, A Briddon

  • 1Charles Dent Metabolic Unit, National Hospital for Neurology and Neurosurgery, London, UK.

Journal of Inherited Metabolic Disease
|December 23, 2006
PubMed

Insights

In homocystinuria (HCU), free homocystine acts as a cystine surrogate, restoring thiol redox balance. Supplementing cystine is recommended when cysteine levels drop below 170 micromol/L.

Area of Science:

  • Biochemistry
  • Metabolic Disorders

Background:

  • Thiol redox balance, measured by free/bound cyst(e)ine ratios, is constant in healthy individuals.
  • Severe homocystinuria (HCU) disrupts cyst(e)ine metabolism, altering thiol redox.
  • Homocyst(e)ine moieties can compensate for reduced cyst(e)ine in HCU patients.

Purpose of the Study:

  • To investigate the role of homocyst(e)ine as a cystine surrogate in HCU.
  • To determine the relationship between free/bound homocyst(e)ine ratios and total cysteine concentrations.
  • To establish criteria for cyst(e)ine supplementation in HCU.

Main Methods:

  • Analysis of free/bound homocyst(e)ine ratios in 47 HCU patients.
  • Assessment of patients with various HCU subtypes (cobalamin C defect, MTHFR deficiency, pyridoxine-responsive/nonresponsive HCU).
  • Correlation of homocyst(e)ine ratios with total cysteine levels.

Main Results:

  • A relative increase in free homocystine was observed as a surrogate for free cystine.
  • This surrogate effect was noted when total cysteine concentrations fell below 170 micromol/L.
  • The findings were consistent across different HCU patient groups.

Conclusions:

  • Homocyst(e)ine can act as a functional surrogate for cystine in maintaining thiol redox in HCU.
  • A threshold of 170 micromol/L for total cysteine concentration can guide cystine supplementation decisions.
  • This study provides a rationale and algorithm for cystine supplementation in managing HCU.

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