Phenylketonuria (PKU) is a rare genetic disease that affects the conversion of the amino acid phenylalanine (Phe) into the amino acid tyrosine (Tyr). (Amino acids are building blocks of proteins.)
Among its symptoms, people with PKU often experience skin problems such as rashes and sensitivity to light.
How does PKU affect the skin?
Mutations in the PAH gene cause PKU. This gene contains instructions for cells to make the enzyme phenylalanine hydroxylase (PH). PH converts phenylalanine into Tyr. When there isn’t enough of the enzyme or if it doesn’t function properly, Phe levels begin to build up in the body.
The high levels of Phe and lower levels of tyrosine affect the skin and nervous system, leading to the disease’s symptoms. These include fair skin, and hair and eye colors due to a reduction in melanin production. (Tyr is a precursor of melanin.) Increased levels of Phe and the products of its breakdown can also cause photosensitivity, eczema, and a musty smell to the skin and body. Researchers have also reported scleroderma-like skin lesions in patients with PKU.
Skin therapy options
Diet
As with many of the symptoms of PKU, dietary restriction of Phe can help improve skin issues. Removing phenylalanine from the diet and supplementing it with extra tyrosine can result in skin and hair darkening. It can also help reduce the occurrence of eczema. Reintroducing Phe into the diet can reverse these skin improvements, and lead to the reappearance of symptoms.
Eczema treatment
Eczema, or atopic dermatitis, can manifest in several forms, including dry, itchy, and cracked skin, and reddish-brown patches. Several treatments are available to help relieve eczema, including medications, treatment with narrow bands of artificial ultraviolet light, wet dressings, corticosteroid creams, and relaxation or counseling services to deal with the desire to scratch.
Medication
Two treatments for PKU are approved by the U.S. Food and Drug Administration. Kuvan (sapropterin dihydrochloride), which helps to stimulate the conversion of Phe to Tyr via residual PH enzymes the body is able to make, was approved in 2007. Palynziq (pegvaliase-pqpz), approved in 2018, helps to lower blood levels of Phe. These treatments may also reduce the skin symptoms that PKU causes.
Last updated: Sept. 17, 2020
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