Tyrosinemia, type III (TYR III) is a rare genetic condition. TYR III results from a mutation or error in a person’s DNA or genes. Due to this mistake, people with TYR III have problems breaking down certain protein building blocks called amino acids. TYR III occurs when the body either does not make enough or makes non-working TYR III enzyme, 4-hydrocyphenylpyruvate dioxygenase (HPD). Enzymes are special proteins that help break down the food we eat into the pieces our body can use, for example to help make energy. If there is not enough working HPD, then the body cannot break down the amino acid tyrosine. This causes high levels of tyrosine in the liver, kidneys and central nervous system which may become toxic and cause damage. High levels of tyrosine may be detected in the blood and urine.
Those with TYR III have signs that are highly variable. TYR III is the rarest of the tyrosinemias, with about 20 cases reported. Some individuals show no signs of the disorder. Others may have developmental delay, behavioral problems such as ADHD, seizures, small head size (microcephaly), lack of muscle control (ataxia), involuntary shakiness or quivering (tremor) and/or weak muscles (hypotonia). In 75% of the reported cases, the individual with TYR III had intellectual disabilities. Although it is not certain if a special diet will prevent symptoms from developing, recently reported cases suggest that it is important to follow a diet low in phenylalanine and tyrosine in the first year of life. Many babies are screened for TYR III at birth so that treatment can begin early, however the conditions included in newborn screening differ from state to state. For more information, visit http://www.babysfirsttest.org. TYR III is an autosomal recessive trait. A genetic counselor can help you understand the genetics. Talk with your baby’s doctor and specialists to decide on the best treatment plan. Support groups are also a good source of information.