New treatment approved for rare genetic disease

 PKU can cause severe mental retardation if not treated.
PKU can cause severe mental retardation if not treated.

For many years the only treatment for phenylketonuria (PKU) has been adherence to a strict low phenylalanine diet for life. However, palynziq (pegvaliase-pqpz) has now been approved by the US Food and Drug Administration (FDA) to treat PKU. 

What is PKU? 

PKU is a rare genetic disorder in which an amino acid phenylanlanine builds up in the body as a result of the body's inability to create the enzyme phenylalanine hydroxylase, needed to break down the phenylalanine and convert it into tyrosine. 

The name of the condition comes from the fact that the levels of phenylketones are high enough that they can be detected in the urine. 

The disorder affects about one in 10 000 to 15 000 people in the United States. Left untreated, it can lead to serious learning, developmental and psychiatric disabilities, the FDA said in a news release. 

Symptoms of PKU

Newborns with PKU initially do not show any symptoms of the condition. However, without immediate treatment, it becomes apparent within a few months.

PKU's most common symptoms include a musty odour in the breath, skin or urine, caused by too much phenylalanine in the body. Neurological problems may include seizures, behavioural and social issues as well as intellectual disability. As a result of the phenylalanine being unable to transform into melanin, the pigment responsible for hair and skin tone, often those with PKU will have fair skin and blue eyes. Other symptoms include an abnormally small head (microcephaly), skin rashes and psychiatric disorders.

Treatment of PKU 

Palynziq's safety and effectiveness were evaluated in clinical studies involving people with high concentrations of blood phenylalanine. The most common side effects of the enzyme substitution therapy were injection-site reactions, allergic-like hypersensitivity reactions, joint pain, headache, itchy skin, nausea, dizziness and abdominal pain.

The drug's label warns of a less-common risk of life-threatening anaphylaxis, which the agency said most often occurred when the dosage was increased during the first year of treatment.

Palynziq is produced by BioMarin Pharmaceutical, based in Novato, California. 

Image credit: iStock

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