Homocystinuria

Definition:

An inherited disorder involving the metabolism of the amino acid methionine.

Causes, incidence, and risk factors:

Homocystinuria is inherited as an autosomal recessive trait. Constant findings in homocystinuria are myopia (nearsightedness), dislocation of the lens of the eye, and a tendency to develop venous and arterial clots (thrombi). 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 myopia. Some degree of mental retardation is usually seen but some affected people have normal IQs. When mental retardation is present, it is generally progressive.

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

Affected people commonly develop blood clots. Thromboembolic episodes can cause damage in any tissue the embolus lodges in. Emboli to the brain can produce severe sequela.