Homocystinuria of Vitamin B6 Dependent Type

In three patients with homocystinuria, an intramuscular injection of vitamin Bs was done and its effect was investigated clinically and biochemically. In only one of the patients, the vitamin B6 administration brought about almost complete disappearance of urinary homocystine and an in vitro study on cystathionine synthetase activity of the liver revealed that the enzyme activity was activated when an excess of pyridoxal phosphate was added to the assay system. In the remaining two patients with homocystinuria, no beneficial effect was ob-served clinically and biochemically by treatment with pyridoxal phosphate. In one of them an in vitro study of the enzyme assay of the liver was done, showing that the enzyme activity was not influenced by addition of an excess of pyridoxal phosphate to the assay system. These findings suggest that there are two types of homocystinuria, one being vitamin Bs dependent and the other not dependent on vitamin B6.