Cystathionine beta synthase deficiency

Alternative names

Homocystinuria

Definition

Homocystinuria is an inherited disorder of the metabolism of the amino acid methionine.

Causes, incidence, and risk factors

Homocystinuria is inherited as an autosomal recessive trait, which means that the child must inherit the defective gene from both parents to be seriously affected. Typical problems seen in people with homocystinuria are nearsightedness, dislocation of the lens of the eye, and a tendency to develop blood clots in the veins and arteries.

Newborn infants appear normal, and early symptoms, if present at all, are vague and may occur as mildly delayed development or failure to thrive. Increasing visual problems may lead to diagnosis of this condition when the child, on examination, is discovered to have dislocated lenses and nearsightedness.

Some degree of mental retardation is usually seen, but some affected people have normal IQs. When mental retardation is present, it is generally progressive if left untreated. The condition can also increase the risk for psychiatric disorders.

Homocystinuria has several features in common with Marfan syndrome, including dislocation of the lens; a tall, thin build with long limbs; spidery fingers (arachnodactyly); and a pectus deformity of the chest. In addition, affected people may have high arches of the feet (pes cavus), knock-knees (genu valgum), and a curved spine (scoliosis).

Unlike Marfan syndrome, in which the joints tend to be "loose," in homocysturia the joints tend to be "tight." Individuals with homocysturia may also have generalized osteoporosis.

Affected people commonly develop blood clots. These clots can dislodge and travel (form an embolus) and damage any tissue in which the clot lodges. Clots that travel to the brain can cause stroke, for example.

Symptoms

• A family history of homocystinuria
  
• Nearsightedness
  
• Flush across the cheeks
  
• Tall, thin build
  
• Long limbs
  
• High-arched feet (pes cavus)
  
• Knock-knees (genu valgum)
  
• Pectus excavatum
  
• Pectus carinatum
  
• Mental retardation
  
• Psychiatric disease
  

Signs and tests

During a physical examination of the child, the health care provider may notice a tall, thin (Marfanoid) stature with pectus deformity of the chest or scoliosis. If there is poor or double vision, an ophthalmologist should perform a dilated eye exam where dislocation of the lens of the eye or nearsightedness may be observed.