Homocystinuria is a hereditary disease caused by enzyme deficiency during methionine metabolism, and is a rare syndrome involving the eye, cardiovascular, skeletal, and nervous systems. It is an autosomal recessive disease, mainly caused by consanguineous marriage of parents, and has been reported in China. There are three types of the disease: I. Cystathionine synthase deficiency type. Children with this type are normal at birth, and most of them start to suffer from the disease at 5-9 months after birth, with delayed development, short stature, slow reaction, language disorder, intellectual disability, and epileptic seizures. Lens subluxation occurs around the age of 10 years, patients in adolescence can appear osteoporosis, scoliosis, thoracic deformity, high palatal arches, spider nevus, but also prone to fracture, skin vascular lesions often cause reticular cyanotic spots on the skin, resulting in thinning of the skin, facial flushing, thinning of the hair. Methyltransferase deficiency. The clinical manifestations of this type vary in severity, including mental retardation, Marfan syndrome-like appearance, backward physical development, recurrent infections, and neurological diseases of different degrees. 5,10-N-methylenetetrahydrofolate reductase deficiency. It is clinically different from the above two types in its manifestations, mainly neurological symptoms, such as convulsions, mental retardation, catatonia, peripheral neuropathy, myopathy, schizophrenia-like manifestations, increased muscle tone, hyperreflexia of tendons, ataxia, and generally no vascular, skeletal or crystalline symptoms. The disease is mainly diagnosed prenatally by testing the enzymatic activity of amniotic fluid cells. The homocysteine assay in urine is used, and the activity of skin fibroblast enzymes can also be measured. x-rays show osteoporosis, biconcave vertebrae, and scoliosis, among others. Diagnosis is based on clinical manifestations and laboratory tests. Treatment of the synthetase-deficient form consists of limiting methionine intake and applying large amounts of vitamins. For the methyltransferase-deficient and reduced forms, methionine intake should not be restricted, but its intake should still be appropriate.