[Clinical characteristics and CBS gene analysis of 13 cases with classic homocystinuria]

Objective: To analyze the clinical features and CBS gene variants of 13 patients with classic homocystinuria, and the strategies of individual treatment and prevention were explored. Methods: The general information, clinical manifestations, laboratory tests, cranial images, CBS gene variants, diagnosis and therapeutic strategies of 13 patients with classic homocystinuria admitted to the Department of Pediatrics of Children's Hospital Affiliated to Zhengzhou University and Peking University First Hospital from November 2013 to June 2021 were analyzed retrospectively. Results: There were 13 patients diagnosed at the age of 10 days to 14 years, 6 were male and 7 were female. There were 3 patients detected by newborn screening and received treatment at the asymptomatic stage. There were 10 patients clinically diagnosed at the age of 5 to 14 years. Their symptoms appeared at age of 1 to 6 years. The major clinical manifestations were marfanoid features, lens dislocation and (or) myopia, developmental delay, osteoporosis, and cardiovascular diseases. Brain magnetic resonance imaging showed asymmetric infarcts in 4 patients and hypomyelination in 1 case. Increased blood methionine, plasma total homocysteine and urinary total homocysteine with normal urinary methylmalonic acid were found in 13 patients. The biochemical features were consistent with classic homocystinuria. Totally 18 variants were identified in CBS gene of 13 patients, 10 variants were novel and 8 were reported. only 1 patient was partially responsive to vitamin B₆ treatment, while 12 cases were non-responsive. They were mainly treated with low methionine diet and betaine supplement. Three vitamin B₆ non-responsive cases received liver transplantation at age of 3, 8 and 8 years, respectively. Their blood methionine and total homocysteine returned to normal within a week after liver transplantation. One patient died. Prenatal diagnosis was performed for a fetus when the mother was pregnant again. Two pathogenic CBS gene variants were identified from the amniocytes as same as the proband. Conclusions: The clinical manifestations of classic homocystinuria are complex and variable. Blood amino acid analysis, serum or urine total homocysteine assay and gene analysis are critical for its diagnosis. There were 10 novel CBS gene varients were identified expanding the CBS gene varient spectrum. Liver transplantation is an effective treatment. Prenatal diagnosis is important to prevent classic homocysteinuria.