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Metabolic diseases

What is a metabolic disease ?

The liver manufactures enzymes and stores them.

The food that we eat is “broken down” (degraded) by these enzymes into small molecules, which serve as fuel for the body.

A person with a metabolic disease does not produce an enzyme or produces an insufficient amount of an enzyme.

Some “chunks” of nutrients (that were not degraded) then accumulate in the body and poison it.

There are several metabolic diseases and they can affect the metabolism of proteins (tyrosinemia, phenylketonuria, maple syrup disease), sugars (glycogenosis, congenital fructose intolerance, galactosemia) and lipids.

They can also involve processes that take place inside the cell, which is called mitochondrial diseases or lysosomal diseases.

Overall, metabolic diseases occur in 1 newborn out of 800 to 2500 births.

How are they transmitted?

Most are hereditary and are inherited in an autosomal recessive manner. In order for the disease to manifest itself, a child must have inherited two defective (recessive) genes, one from each parent.

If the parents are not sick, they are considered to be “carriers” of this recessive gene.

What are the symptoms?

They appear in various ways, sometimes at birth or after a period ranging from a few months to a few years.

They are manifest in different ways, for example through:

  • Yellowing of the skin (jaundice),
  • Abdominal distension,
  • Liver failure,
  • A delay in weight gain,
  • Vomiting,
  • Diarrhea,
  • Neurological symptoms: difficulties waking up, etc.
  • Kidney function disorders

In infants, the first symptoms appear suddenly and abruptly. These symptoms are often triggered by eating a new food or by stress as with a childhood disease.

What are the treatments?

Early diagnosis is essential and often determines the disease's progress. For some metabolic disorders, a very strict diet should be followed.
In this way, the disease symptoms can be lowered. This diet consists of eliminating molecules in the child's food that are not broken down.

For example, with tyrosinemia, tyrosine is not allowed. For other metabolic diseases, there are medicinal treatments.

But often, since only gene therapy would be effective, the treatments offered are limited to controlling complications. While waiting for gene therapy, liver transplantation is often the treatment of choice for metabolic diseases.

Transplantation is focused on giving the child the missing enzyme to ensure a future that is as normal as possible, on the one hand, and to spare them the dietary constraints on the other hand.

What is the prognosis?

The prognosis for a metabolic disease varies based on the individual and the type of enzyme deficiency.

However, there are two general principles can be retained:

  • the more the attacks occur in young people, the more severe they are
  • the prognosis with or without a liver transplant depends on the number of organs affected by the deficit.