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Homocystinuria (HCU): heel prick screening

Homocystinuria (HCU) is an inherited condition caused by a gene change. HCU can cause a build-up of certain amino acids in the blood.

Our bodies break down the protein in foods, such as meat and fish, into amino acids, which are the "building blocks" of protein.

High levels of these amino acids can lead to problems such as:

  • eye problems
  • problems with brain development
  • bone disorders
  • blood clots
  • strokes

Babies born in Ireland with HCU

Around 1 in every 66,000 babies born in Ireland has HCU.

Babies with HCU inherit one changed gene from each parent.

How heel prick screening can help

Babies are checked for HCU as part of heel prick screening. They are offered heel prick screening when they are around 5 days old. This test also checks for other conditions.

A midwife or nurse takes a few drops of blood from your baby's heel using a special device.

Babies with HCU benefit from early diagnosis and treatment. Milder forms of HCU may not be detected by screening.

If the heel prick suggests your baby may have HCU, they will be referred to a specialist.

Your baby will then be put on a special diet and medicine. This is a protein-restricted diet. It includes supplements of vitamins, amino acids and minerals.

This diet is for life. It will reduce the risk of your baby developing the problems that HCU can cause.

Heel prick screening

Page last reviewed: 16 September 2025
Next review due: 16 September 2028