Saving lives with genetics: newborn screening
While screening at birth targets very rare diseases, this early diagnosis can have huge benefits for the small number of affected babies
At the start of 2015, the NHS Newborn Blood Spot Screening Programme was expanded to include four additional conditions.
Newborn screening is a long-established practice, checking newborn babies for potential medical problems or abnormalities at, or shortly after, birth to optimise their care. It incorporates checks for some rare inherited conditions.
Here’s how the programme began, what it now covers, and why.
PKU
The programme began in the UK in the late 1950s when newborn checks for the condition phenylketonuria (PKU) were introduced. PKU is caused by mutations in the gene for a crucial metabolic enzyme, phenylalanine hydroxylase. Without sufficient functional enzyme, the body is unable to break down phenylalanine from food; it accumulates in the body and fairly quickly results in irreversible brain damage.
However, if PKU is identified early in infancy (before symptoms develop), then careful dietary control to avoid phenylalanine intake allows normal development. Athough PKU is very rare, screening the entire newborn population is considered worthwhile because the harm it prevents in the few children affected is very great.
Guthrie cards and CHT
In the early 1970s, the characteristic newborn bloodspot or Guthrie cards were introduced to UK newborn screening, and in 1980 a new condition was introduced, testing for congenital hypothyroidism (CHT), a form of thyroxine deficiency that can cause irreversible physical and mental disability if not promptly identified and treated with thyroxine hormone.
Sickle cell and cystic fibrosis
The panel of conditions was then further expanded to include sickle cell disease and cystic fibrosis, both heritable genetic disorders. Whilst there is no definitive cure for these conditions at present, early diagnosis and treatment has medical benefits, helping to prevent complications and limit or slow long-term damage.
MCADD
The next step forward for newborn screening came with the addition of the condition medium-chain acyl-CoA dehydrogenase deficiency (MCADD) in 2009. MCADD is another rare genetic metabolic disorder like PKU, for which careful dietary management can prevent serious harm or death.
Importantly, inclusion of MCADD in newborn screening necessitated the introduction of a new testing technology known as tandem mass spectrometry. This allows precise analysis of specific metabolites, ideal for the detection of inherited metabolic diseases; it could therefore be considered a form of genetic test, since it allows diagnosis of genetic diseases – but without the use of any DNA.
Why the list of conditions is expanding
Introduction of tandem mass spectrometry also opened the door for further expansion of newborn screening to include many more such rare inherited metabolic conditions, since the additional cost implications are very small. Coupled with the rapid expansion in knowledge about the underlying genetic causes of rare conditions, this has created scope to identify the diseases and provide vital, and in many cases life-saving, treatment for affected newborn babies.
Some countries have seen a rapid expansion of their newborn screening panels; the US now has a recommended panel of 30 such conditions. The UK’s approach has been more conservative, but in January 2015 Public Health England announced that testing for four new rare genetic metabolic disorders had begun:
- maple syrup urine disease;
- isovaleric acidaemia;
- glutaric aciduria type 1; and
- homocystinuria.
More may follow, although for very rare conditions it is difficult to generate robust evidence to demonstrate the value of screening, because so few babies are affected.
–
