Tyrosinemia type 3

Definition

Tyrosinemia type 3 is a genetic disorder characterized by elevated blood levels of the amino acid tyrosine, a building block of most proteins.

Epidemiology

Tyrosinemia type III is very rare; only a few cases have been reported.

Cause

• This condition is caused by a deficiency of the enzyme 4-hydroxyphenylpyruvate dioxygenase, one of the enzymes required for the multi-step process that breaks down tyrosine.
• This enzyme shortage is caused by mutations in the HPD gene.

Inheritance

Autosomal recessive inheritance, a 25% chance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Signs and symptoms

Characteristic features include intellectual disability, seizures, and periodic loss of balance and coordination (intermittent ataxia).

Diagnosis

Metabolic screening on the basis of elevated serum level of tyrosine ranging from 425 to 535 μmol/L (normal values: 29-86 μmol/L), and elevated urinary excretion of p-hydroxyphenyl derivatives confirmed genetically with the homozygous c.479A > G (p.Tyr160Cys) missense change in the HPD gene.

NIH genetic and rare disease info

• NIH info on Tyrosinemia type 3

Tyrosinemia type 3 is a rare disease.