Can Ficicioglu, MD, PhD, Clinical Director of the Metabolic Disease Program at Children’s Hospital of Philadelphia (CHOP), discusses the management of homocystinuria.

Homocystinuria is a rare congenital metabolic disease characterized by extremely elevated levels of homocysteine and its precursor, methionine. Homocystinuria is caused by an inherited deficiency in the enzyme, cystathionine beta-synthase. When cystathionine beta-synthase is absent, homocysteine builds up in the blood and urine, putting patients at risk of multisystem complications, including acute thromboembolic events, optical damage from lens dislocation, skeletal deficiencies, and neurocognitive impairments.

As Dr. Ficicioglu explains, the mainstay of treatment of homocystinuria is an extremely restrictive low-methionine diet. Newborns are given a specialized formula that does not contain methionine but does contain the other essential amino acids. Betaine, which helps convert homocysteine into methionine, is also commonly used to treat people with homocystinuria, as are vitamins B12 and B6.  Unfortunately, adherence to treatment, more specifically the strict diet, is often very low in persons with this rare condition.

Recently, the FDA granted fast track and orphan drug designations to SYNB1353, an investigational treatment for homocystinuria, after positive top-line data from a phase 1 trial.

To learn more about homocystinuria and other rare metabolic disorders, visit