Phenylalanine hydroxylase deficiency (including PKU)

Phenylalanine hydroxylase deficiency (PHD) can affect the body's ability to process phenylalanine, an amino acid found mostly within food-based proteins and artificial sweeteners. There are three main types of PHD, that range in how serious they are. The three types are: classic phenylketonuria (PKU), variant phenylketonuria and benign hyperphenylalaninemia (HPA).

The most serious form of the condition, PKU, can cause serious developmental and intellectual disabilities. The mildest form of the condition, benign HPA, often has little to no symptoms. If treatment is needed, PHD can be well managed with a specific diet that is low in phenylalanine.

Quick facts about phenylalanine hydroxylase deficiency (including PKU)
Genes: PAH
Inheritance: Autosomal Recessive
Alternative Names: PKU
Relevant resources for phenylalanine hydroxylase deficiency (including PKU)

A quick genetics rundown

As humans we have about 23,000 genes. These genes are like tiny instruction manuals that influence our health, growth and development. We inherit half of our genes from our biological mum and the other half from our biological dad. These genes are lined up on structures called chromosomes. Most of us have 23 pairs of chromosomes. The first 22 pairs are called autosomes and for the most part - these are the same among men and women. The 23rd pair determine our sex - two X chromosomes for a female and one X and one Y chromosome for males.

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How is phenylalanine hydroxylase deficiency (including PKU) inherited?

phenylalanine hydroxylase deficiency (including PKU) is known as an autosomal recessive condition. For autosomal recessive conditions, if a person has a variation in one copy of their gene, they are a carrier. This means that they are healthy because they also have a working copy of the gene. But, they can still pass their non-working copy to their child.

If the other parent also happens to be a carrier of the same gene, there is a 25% (1 in 4) chance that they both pass this gene variation on to their child — and as such, have a child affected by the disease.

If both parents are carriers of phenylalanine hydroxylase deficiency (including PKU), there’s a one in four chance that their children could develop symptoms.
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What is carrier screening?

Carrier testing is like a checkup for your genes. It tests to see if you carry a gene variation that could cause a serious genetic disease in your child. Eugene offers an inclusive genetic carrier screening panel that includes phenylalanine hydroxylase deficiency (including PKU), but there's a total 301 conditions that can be tested.

Eugene’s carrier test is a clinical grade test that can be done from the comfort of your own home — it’s just a saliva test. You're also paired with a genetic counsellor who provides mindful support and guidance every step of the way.

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Should parents screen for phenylalanine hydroxylase deficiency (including PKU) before or early in pregnancy?

The biggest benefit of screening for phenylalanine hydroxylase deficiency (including PKU) is that it can help future parents understand their reproductive risk so they can be ready and empowered to make more informed decisions. If neither partner are carriers, it provides reassurance and peace of mind that the risk of having a child with a genetic disease is low.

Since 90% of children that have a recessive genetic disease like phenylalanine hydroxylase deficiency (including PKU) had no previous family history of it, it often feels completely out of the blue for the parents. Getting screened is a way to know this risk in advance, which can help familes manage or even prevent the disease in the first place.

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