Many children are born with these chemical defects. Whilst there is no cure, some can be treated if diagnosed quickly enough. Some of the children will grow up to lead normal or nearly normal lives, although they may have to have special diets or may be dependent on prescribed drugs to stay alive. Sadly some of the children are not diagnosed quickly enough, or even when diagnosed there is no available treatment or cure and they die.

Many of the individual conditions are very rare indeed, but thousands of children suffer from them collectively. The impact on a family is huge. Because these conditions are chemical imbalances they can be very complex to understand. If a child is born with 'a deficiency of the enzyme that cleaves adrenocorticotrophic hormone' it is a lot for a non-medical person to take on board and more difficult still to explain to granny! The Internet is a fantastic resource for those with rare medical conditions. There are many websites relating to very rare medical conditions. Comparing information with others can be really helpful both in terms of helpful factual advice and emotional support.

Metabolism is the name given to the many complicated chemical reactions that occur in the body. You can develop a metabolic disorder, diabetes, for instance - or you can be born with a disorder, that is a congenital defect.

There are around 1,300 currently identified metabolic diseases, which are caused by the absence or fault in an enzyme (or the catalyst) responsible for chemical reactions. You may remember the film 'Lorenzo's Oil' which was about a boy with a congenital metabolic disease called ALD (Adrenoleukodystrophy). If just one chemical in the body fails, it can lead to a chain reaction of defects, with some chemicals building up one side of the defect and a deficiency of a chemical on the other. Either a build up of a toxic chemical or a deficiency of an essential chemical can be fatal.