Tyrosinemia type II is an autosomal recessive condition with onset between ages 2 and 4 years, when painful circumscribed callus

Callus

A callus is an especially toughened area of skin which has become relatively thick and hard in response to repeated friction, pressure, or other irritation. Rubbing that is too frequent or forceful will cause blisters rather than allow calluses to form. Since repeated contact is required, calluses...

es develop on the pressure point

Pressure point

A pressure point in the field of martial arts refers to an area on the human body that may produce significant pain or other effects when manipulated in a specific manner...

s of the palm of the hand and sole of the foot

Sole (foot)

The sole is the bottom of the foot.In humans the sole of the foot is anatomically referred to as the plantar aspect. The equivalent surface in ungulates is the hoof.- Human sole :...

.

Pathophysiology

Type II tyrosinemia is caused by a deficiency of the enzyme tyrosine aminotransferase

Tyrosine aminotransferase

Tyrosine aminotransferase is an enzyme present in the liver and catalyzes the conversion of tyrosine to 4-hydroxyphenylpyruvate. In humans, the tyrosine aminotransferase protein is encoded by the TAT gene...

 , encoded by the gene TAT. Tyrosine aminotransferase is the first in a series of five enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s that converts tyrosine to smaller molecules, which are excreted by the kidney

Kidney

The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s or used in reactions that produce energy. This form of the disorder can affect the eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

s, skin

Human skin

The human skin is the outer covering of the body. In humans, it is the largest organ of the integumentary system. The skin has multiple layers of ectodermal tissue and guards the underlying muscles, bones, ligaments and internal organs. Human skin is similar to that of most other mammals,...

, and mental development. Symptoms often begin in early childhood and include excessive tearing

Tears

Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....

, abnormal sensitivity to light (photophobia

Photophobia

Photophobia is a symptom of abnormal intolerance to visual perception of light. As a medical symptom photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical photosensitivity of the eyes, though the term...

), eye pain and redness, and painful skin lesions on the palms and soles. About half of individuals with type II tyrosinemia are also mentally challenged. Type II tyrosinemia occurs in fewer than 1 in 250,000 individuals.