Effects on Overall Survival

Available data for historical controls show that patients presenting with HT-1 under 2 months of age and treated with dietary restrictions alone had 2 and 4-year survival probabilities of 29% and 29%, respectively. This compares to 2 and 4-year survival probabilities of 88% and 88%, respectively, for patients presenting with HT-1 under 2 months of age and treated with dietary restrictions and Nitisinone in this study. Data for historical controls show that patients presenting with HT-1 under 6 months of age had 2 and 4-year survival probabilities of 74% and 60%, respectively. This compares to 2 and 4-year survival probabilities of 94% and 94%, respectively, for patients presenting with HT-1 under 6 months of age and treated with dietary restrictions and Nitisinone in this study.

Although the long term prognosis of patients treated with Nitisinone with regard to hepatic function is not yet known, the results of this clinical study suggest a marked reduction (>75%) in the risk of early onset liver failure that characterizes the natural history of HT-1.

Effect on Porphyrin Metabolism

Three cases of porphyric crisis, one of which was fatal, were observed in three patients during the clinical study and in continued clinical follow-up (0.3% cases per year). This compares to the incidence of 5-20% cases per year expected as part of the natural history of the disorder.

Effect on Renal Function

Renal function was investigated specifically in the subgroup of patients exhibiting signs of renal dysfunction prior to treatment. At the one-year visit, both urine excretion of amino acids and serum concentration of phosphate were within the reference range in this subgroup. Urinary alpha-1-microglobulin, used to estimate tubular function, was increased at the start of the study in this subgroup but was within the normal reference limits after 1 year of treatment.

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