What is it?
It is an alteration of the metabolism of biotin. It is due to the deficiency of the biotinidase enzyme. This results in a multiple deficiency in carboxylases. Its characteristic metabolic consequences are due to the role of carboxylases, substances that are involved in gluconeogenesis, that is, the synthesis of glucose, in the synthesis of fatty acids and in the catabolism of amino acids.
Biotin is a water-soluble vitamin B complex. It is present in low concentrations in multiple foods: liver, kidney, egg yolk, vegetables, cereals, etc.
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Intestinal bacteria can also synthesize it. They help, in this way, to complement the biotin provided by the diet.
It is a hereditary disease.
How is the inheritance?
It is autosomal recessive. Parents of children with the disease do not necessarily suffer it.
When both parents are carriers, there is a 25% chance in each pregnancy that the child has the disease. 50% of children can be carriers, just like parents. Finally, there is a 25% chance that the child has two genes that work correctly and is healthy and not a carrier.
It is very frequent?
It's weird
The prevalence, which is the number of individuals of a group or a population that have a certain characteristic, at a given moment, is estimated at 1 per 75.0000.
And the symptoms?
When the baby begins to feed, the milk proteins degrade and release all the amino acids. Some (isoleucine, valine and leucine) do not degrade well, due to biotin deficiency. Gluconeogenesis (glucose synthesis) does not work well either. This can cause hypoglycemia, with elevation of ketone bodies and lactic acidemia.
Even though the newborn uses maternal biotin in the neonatal period, it will soon need an active biotin recycling to cover its metabolic needs. And it will begin to manifest signs of multiple carboxylase deficiency. The toxic compounds will begin to accumulate and the child will present symptoms of intoxication that can be manifested according to the type of enzyme deficit:
a) If the deficit is total, may appear:
- vomiting
- food rejection
- seizures
- dermatitis (probably due to the defect of fatty acid synthesis)
- muscle flaccidity
- skin rash
- hair loss
- Hearing loss
- fungal infections
- developmental delay
- optic nerve atrophy (loss of vision)
- loss of defenses in the immune system.
- Even in the long term, the child can develop deafness and cognitive impairment.
b) Children with partial deficit only have symptoms in phases of stress:
Symptoms of hypoglycemia (see figure): weakness, tremors, dizziness, sweaty and cold skin.
If left untreated, hypoglycaemia can even lead to coma and death.
Should neonatal screening be done?
YES. Why:
- Although its incidence is low, it is a process with high mortality and morbidity. There is an effective treatment that will be more effective, the sooner it is established.
- On the other hand, the symptomatic range of this disease is so broad and non-specific, that its clinical diagnosis is difficult and, often, late.
- The screening test is easy to perform. It has a low cost and is safe and effective.
Universal neonatal screening is the study of all people. It is performed from the blood obtained from the heel puncture in the newborn. A piece of paper is impregnated with blood and studied by a colorimetric method.
And the definitive diagnosis?
It is done by:
- Quantification of organic acids in urine, in an isolated urination.
- Quantification of acylcarnitines in serum or plasma.
- Determination of the biotinidase activity in serum.
- Determination of mitochondrial carboxylase activities in lymphocytes (Before treating the child).
- Molecular analysis of the gene. It has to be done on anticoagulated blood.
And the treatment?
It is treated with biotin 5-10 mg / day in severe cases and between 1-5 mg / day in partial deficiency.
The treatment must be maintained throughout life.
And the forecast?
It is very good if it is diagnosed and treated early.
Some of the symptoms, such as hearing loss or optic atrophy, do not revert with the treatment. Hence the importance of early diagnosis and treatment. Yes they revert others: cutaneous, seizures and problems of walking.
And what to do in the family?
GENETIC ADVICE must be done. Parents are, necessarily, carriers.
The brothers must be tested.