Tyrosinemia type 2

Alternate names

Tyrosinemia type II; Richner Hanhart syndrome; TAT deficiency; Tyrosine transaminase deficiency; Keratosis palmoplantaris with corneal dystrophy; Oregon type tyrosinemia; Tyrosinosis oculocutaneous type; Tyrosine aminotransferase deficiency; Oculocutaneous tyrosinemia

Definition

Tyrosinemia type 2 is a genetic disorder in which individuals have elevated blood levels of the amino acid tyrosine, a building block of most proteins. This condition can affect the eyes, skin, and intellectual development.

Epidemiology

Tyrosinemia type II occurs in fewer than 1 in 250,000 individuals worldwide.

Cause

Tyrosinemia type 2 is caused by a deficiency of the enzyme tyrosine aminotransferase, one of the enzymes required for the multi-step process that breaks down tyrosine. This enzyme shortage is caused by mutations in the TAT gene.

• In the liver, enzymes break down tyrosine in a five step process, resulting in molecules that are either excreted by the kidneys or used to produce energy or make other substances in the body.
• The enzyme produced from the TAT gene, called tyrosine aminotransferase enzyme, is involved at the first step in the process.

Gene mutation

Mutations in the FAH gene cause a decrease in the activity of one of the enzymes in the breakdown of tyrosine. As a result, tyrosine and its byproducts accumulate to toxic levels, which can cause damage and death to cells in the liver, kidneys, nervous system, and other organs.

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.

Onset

Symptoms of tyrosinemia type 2 often begin in early childhood.

Symptoms

Tyrosinemia type II can affect the eyes, skin, and mental development. Signs and symptoms often begin in early childhood and include eye pain and redness, excessive tearing, abnormal sensitivity to light (photophobia), and thick, painful skin on the palms of their hands and soles of their feet (palmoplantar hyperkeratosis). About 50 percent of individuals with tyrosinemia type II have some degree of intellectual disability.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Corneal opacity
• Intellectual disability(Mental deficiency)
• Palmoplantar keratoderma(Thickening of palms and soles)

30%-79% of people have these symptoms

• Abnormality of amino acid metabolism
• Hyperhidrosis(Excessive sweating)
• Nystagmus(Involuntary, rapid, rhythmic eye movements)
• Photophobia(Extreme sensitivity of the eyes to light)

5%-29% of people have these symptoms

• Abnormality of the nail
• Ataxia
• Malar flattening(Zygomatic flattening)
• Microcephaly(Abnormally small skull)
• Neurological speech impairment(Speech disorder)
• Seizure
• Tremor
• Visual loss(Loss of vision)

Diagnosis

Diagnosis is made based on elevated plasma tyrosine level with skin or eye lesions.

Treatment

The management of tyrosinemia type 2 revolves around dietary restriction of phenylalanine and tyrosine. This controlled diet typically lowers the blood levels of tyrosine, resulting in rapid resolution of the skin and eye symptoms. However, the effects of this controlled diet on central nervous system involvement (mental development) remains unclear. In some cases, skin lesions may be treated with oral retinoids.

Possible complications If tyrosinemia type II and III are not treated, a child might develop: • Poor coordination and balance • Brain damage • Eye problems (Type II) • Behavior changes (Type II) • Skin lesions (Type II) • Seizures (Type III)

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NIH genetic and rare disease info

• NIH info on Tyrosinemia type 2

Tyrosinemia type 2 is a rare disease.

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