Classical HCU

Classical or B6-responsive Homocystinuria

Individuals are born with abnormalities in both their copies of Cystathionine Beta Synthase (CBS).  Some will have been identified by newborn screen; others by symptoms.

Symptoms that can be seen included:

  • blood clots (thrombosis) anywhere including the brain
  • optic lens dislocation (ectopia lentis)
  • tall stature with long arms and legs
  • increased risk of broken bones due to more fragile bones
  • curved spine (scoliosis )
  • some individuals with CBS deficiency can have cognitive problems and mental health issues.


Many of the symptoms can be prevented by early and aggressive therapy. 

  • For those who are B6 responsive, beginning B6 supplementation will improve their homocysteine levels. 
  • Most will be on a special diet low in homocysteine and methionine and will take the medication Betaine (Cystadane ®). 
  • Most will need additional vitamin supplements to prevent deficiencies. 

The goal is to keep one’s total homocysteine below 100 mcmol/L at all times and to not have any further complications.  Some clinics like homocysteine levels to be even lower, and the guidelines recommend keeping below 50 mcmol/L for patients who are responsive to pyridoxine, as those patients can more easily reach that lower level without compromising their nutritional status.  You need to talk to your metabolic geneticist and metabolic dietitian for your specific risks and goals.

Surgery, illness, pregnancy, and immobilization (times when you are not moving for a period of time, like when on a plane or on a long car trip) are times when special attention and procedures are necessary.  If you want to read more (warning this is a copy of the document your medical professional will use so it is long and technical), the guidelines for management and diagnosis are: here