Ciara (9) and Luke (4) Willetts, from Shankill in Dublin who both have PKU.

Ciara (9) and Luke (4) Willetts, from Shankill, Co Dublin, were both diagnosed with PKU through the heel-prick test shortly after birth. Their mother(...)

Lyndsay and Paul Price, with their children, James (13) Alex (8) and Andrew (5), in Shankill, Co Dublin. Photograph: Dara Mac Dónaill

For most parents, the heel prick test is one of those forgettable, standard procedures that their newborn baby goes through during the early, hazy day(...)