Homocystinuria due to CBS deficiency

Homocystinuria due to CBS deficiency is an inherited disorder in which the body is unable to correctly use the amino acid, homocysteine, one of the building blocks of protein.[3151][3152][15056] This form of homocystinuria is caused by a genetic mutation in the CBS gene, which leads to low levels or absence of an enzyme called cystathionine beta-synthase (CBS).[3151][3152][15056] When CBS is absent or not working right, homocysteine and other toxic chemicals build up in the blood and urine. Symptoms of this disorder include poor growth and slow weight gain in infancy.  Additional symptoms include nearsightedness, dislocation of the lens of the eye, an increased risk of blood clots, and developmental problems.[3151] Homocystinuria due to CBS deficiency is inherited in an autosomal recessive pattern.[3151] It is diagnosed by newborn screening, or later in life by blood and urine testing. There are two types of homocystinuria due to CBS deficiency.  One type responds to treatment with vitamin B6 and the other one does not.  Other treatments for this disorder include a protein-restricted diet, betaine treatment, and other supplements. With early treatment, individuals with this condition can have normal growth and development.[3151][15056]