The 29th of June sees the advent of another Metabolic Awareness Week (from CLIMB) in the UK. As a dietetic student with a keen interest in this field, I wanted to take the opportunity of sharing my thoughts on the subject. I will write a series of articles over the coming days to help increase the exposure of Inborn Metabolic Disorders.
Inborn Metabolic Disorders (IMD) or Inborn Errors in Metabolism (IEM) are rare. They are also known as Congenital Errors, these are conditions that are present at birth and are inherited from one or more parents (which are the majority of IMDs).
There are hundreds of IMDs that have already been identified. The most common being:
- Phenylketonuria or PKU.
- Tyrosinaemia.
- Maple Syrup Urine Disease or MSUD.
- Homocystinuria or HCU
- Galactosemia.
These metabolic disorders affect individuals across the world and the incidence of metabolic disorders will vary depending on the ethnic origin of the local population. As an average, the incidence of PKU is approximately 1:10,000 (there can be a large variation across the world with Ireland averaging at 1:4,500 and Finland at the other extreme averaging around 1:100,000.). The incidence of the other disorders are even less common: Galactosemia averaging at 1:60,000 and MSUD / HCU averaging at 1;250,000.
Neonatal screening would be the ideal way for identifying an inborn metabolic disorder, however screening of these disorders is dependant on where you live. In the UK, Phenylketonuria (PKU) is screened everywhere but, in certain areas, they are also piloting MCADD (Medium Chain Acyl-CoA Dehydrogenase Deficiency). In the USA, screening varies by State: some include PKU, Galactosemia, MSUD and HCU, some don’t.Where there is no screening, patients are identified by their symptoms. These include:
- limited response to vomiting,
- diarrhea,
- dehydration,
- respiratory distress,
- lethargy and seizures.
These may be attributed to other causes such as infections. Babies with metabolic disorders of accumulation will show increased deterioration from a period of hours to weeks.
There are also late onset acute / recurrent symptoms and chronic / progressive general symptoms. These impact children, adolescence and even adults and include gastrointestinal, neurological and muscular complaint. There may also be fever or diarrhea: the symptoms can be precipitated by an increase in protein eaten.
There are a number of therapies used to manage these disorders including:
- Nutrition
- Exogenous toxin removal (removing the toxic metabolites).
- Increased vitamin intake.
- Drug therapy.
If left untreated these disorders, can cause irreversible mental retardation, physical disability and even death in affected babies. Over the coming days I will focus on each of the more common disorder highlighted above, giving a more in depth insight into each of them.