Tyrosinemia

Tyrosine is the precursor of some neurotransmitters (for example, dopamine, norepinephrine, adrenaline), hormones (eg, thyroxine), and melanin; deficiency of enzymes involved in their metabolism, leads to a number of syndromes.

Transient tyrosinemia of newborns

Temporary immaturity of enzymes, especially 4-hydroxyphenylpyruvate dioxygenase, sometimes leads to an increase in the level of tyrosine in the blood (usually in premature newborns, especially those receiving high protein foods); metabolites can be detected by routine screening of newborns for phenylketonuria. Most patients have no clinical manifestations, but some have drowsiness and decreased appetite. Tyrosinemia differentiates from phenylketonuria by increasing the level of tyrosine in plasma.

In most cases, spontaneous normalization of the tyrosine level occurs. In patients with clinical symptoms, it is necessary to limit the intake of tyrosine with food [2 g / (kg x day)] and prescribe vitamin C for 200-400 mg orally once a day.

Alcaponuria

Alkaponuria is a rare autosomal recessive disease caused by a deficiency of homozygosinic acid oxidase; the products of oxidation of homogentisic acid accumulate in the skin and color it dark, their joints fall out in the joints. This disease is usually diagnosed in adult patients who have dark skin pigmentation (ochronosis) and arthritis. Urine darkens in air due to the products of oxidation of homogentisic acid. The diagnosis is based on the detection of an elevated level of homogentisinic acid in the urine (more than 4-8 g / 24 hours). There is no effective treatment, however, 1 g of ascorbic acid inside once a day can reduce pigment deposition by increasing renal excretion of homogentisic acid.

[1], [2], [3], [4], [5]

Oculocutaneous albinism

Deficiency of tyrosinase leads to the absence of pigmentation of the skin and the retina, which greatly increases the risk of developing malignant skin tumors, and a significant decrease in vision. Often there is nystagmus, as well as photophobia.

Type I tyrosinemia

Type I tyrosineemia - this disease is inherited by an autosomal recessive type, caused by a deficiency of fumaryl-acetoacetate hydroxylase, an enzyme involved in the metabolism of tyrosine. The disease can manifest as fulminant hepatic insufficiency in the neonatal period or as a sluggish subclinical hepatitis, painful peripheral neuropathy, and impaired renal tubular function (eg, metabolic acidosis with a normal anion gap, hypophosphatemia, vitamin D-resistant rickets) at an older age. In the future, surviving patients have an increased risk of developing liver cancer.

The diagnosis is based on an increase in the level of tyrosine in plasma; confirm the diagnosis by determining the high level of succinylacetone in plasma or urine, as well as the low activity of fumarylacetoacetate hydroxylase in blood cells or liver tissue (with biopsy). Treatment 2 (2-nitro-4-trifluoromethylbenzoyl) -1,3-cyclohexanedione (NTBC) is effective in acute episodes and slows down the progression. It is recommended to use a diet with a low content of phenylalanine and tyrosine. Effective liver transplantation.

Tyrosinemia type II

Type II tyrosinemia is a rare autosomal recessive disease caused by a deficiency of tyrosine transaminase. The accumulation of tyrosine causes ulcers on the skin and cornea. A secondary increase in the level of phenylalanine, despite the fact that it is insignificant, can cause neuropsychiatric disturbances in the absence of treatment. The diagnosis is based on an increase in the level of tyrosine in plasma, lack of succinylacetone in plasma or urine, as well as the determination of reduced enzyme activity in liver biopsy. Tyrosinemia type II is easily treated with mild or moderate restriction of the intake of phenylalanine and tyrosine with food.