OMIM ID:
Tyrosinemia, Type II
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Keratitis is the outstanding ocular manifestation but not all patients have corneal involvement. Symptoms include photophobia, pain, tearing, and redness which may occur as early as one year of age. Corneal neovascularization, ulceration and scarring may lead to decreased visual acuity. Linear and star-like corneal opacities in the epithelium resembling dendrites (pseudodendritic keratitis) have been described together with thickening of the conjunctiva. The corneal lesions do not stain. The conjunctival epithelium, fibrocytes, and blood vessel endothelial cells contain an accumulation of large inclusion bodies and tyrosine crystal-like structures.
Systemic Features
Hydroxyphenylpyruvic acid is elevated in the urine and serum tyrosine levels are increased as the result of a defect in tyrosine aminotransferase. Some patients have severe mental and somatic retardation. The palms and soles can have painful punctate keratosis which may extend to the digits. Developmental milestones such as walking are often delayed. The keratotic lesions may be up to 2 cm in size.
Genetics
Inheritance
Tyrosinemia type II is an autosomal recessive disorder caused by mutations in the tyrosine aminotransferase (TAT) gene at 16q22.1-q22.3.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.