Increased life expectancy in people with untreated phenylketonuria.

The team tracked 17 adults with untreated PKU and intellectual disability.

All lived in the same residential center.

Six had died at an average age of 56. The 11 survivors averaged 56 years old.

People with untreated PKU and ID can live into their 70s.

This is much longer than doctors once thought.

The data came from one center, but the pattern is clear.

Ghaziuddin (1997) used the same case-series method to chart dementia in older adults with ID. Both studies show that ageing adults with ID need long-term planning.

Morad et al. (2007) and McQuaid et al. (2024) looked at constipation and gallstones in residential adults with ID. These papers add common health risks you should watch for as clients age.

McCarron et al. (2022) kept a large share of adults with ID in a study for 11 years. Their success proves you can track ageing clients over decades, just like Macdonall (1998) did.

Plan for decades of service, not just years. Update behavior plans, staff training, and estate planning as if your client will live to 75. Schedule annual health screens for common issues like hypertension and constipation.

Phenylketonuria, or PKU, is an inherited metabolic disorder. It is caused by a change in the gene for an enzyme called phenylalanine hydroxylase (PAH), which the body needs to break down an amino acid called phenylalanine found in protein. PKU is autosomal recessive, meaning a child must inherit one altered gene copy from each parent to have the condition.

When PAH does not work, phenylalanine builds up in the blood and brain. Left untreated from birth, that build-up can cause intellectual disability, seizures, behavioral and psychiatric problems, and other issues. This is why nearly every country now screens newborns with a simple heel-prick blood test (historically the Guthrie test). When PKU is caught early and managed with a lifelong low-phenylalanine diet, most of that harm is prevented.

For people diagnosed at birth and treated with diet, life expectancy is essentially normal. PKU itself is not a directly fatal condition; the danger comes from the untreated build-up of phenylalanine, which modern screening and diet largely prevent. The main modern concern is staying on the diet and, for women with PKU, tightly controlling phenylalanine during pregnancy to protect the baby.

This particular study is important because it looked at the opposite situation: adults with intellectual disability whose PKU had never been treated, from an era before newborn screening existed. Reviewing 17 such residents of a hospital group in Bristol, England, the researchers found that many lived far longer than once assumed. The average age at death was about 56, one deceased woman reached 69, and among those still living the oldest man was 79. In other words, even untreated PKU did not condemn people to a short life, and treated PKU today is compatible with a normal lifespan.