A group of disorders which have in common elevations of tyrosine in the blood and urine secondary to an enzyme deficiency. Type I tyrosinemia features episodic weakness, self-mutilation, hepatic necrosis, renal tubular injury, and seizures and is caused by a deficiency of the enzyme fumarylacetoacetase. Type II tyrosinemia features mental retardation, painful corneal ulcers, and keratoses of the palms and plantar surfaces and is caused by a deficiency of the enzyme TYROSINE TRANSAMINASE. Type III tyrosinemia features mental retardation and is caused by a deficiency of the enzyme 4-HYDROXYPHENYLPYRUVATE DIOXYGENASE. (Menkes, Textbook of Child Neurology, 5th ed, pp42-3)