A 6-year-old tall and thin boy who had failed preparatory exam for schoolentry found to have myopia and subluxation of the ocular lens

(D). Homocystinuria; this is the most common inborn error of methionine metabolism. Approximately 40% of affected patients respond to high doses of vitamin B6 and usually have milder clinical manifestations than those who are unresponsive to vitamin B6 therapy. These patients possess some residual enzyme activity