Inborn errors of metabolism (IEM) are genetic, autosomal, recessive diseases characterized by characterized by the accumulation of toxic substances usually produced by an enzymatic defect. The alteration in a gene produces an enzymatic defect which leads to characteristical biochemical alterations and to a maladaptative phenotype. Nowadays, conditions within the IEM group are recognized where a transporter or post-transcriptional modifiers of gene expression may fail. Its relevance in the group of infrequent diseases (rare) is that they are already considered a set of treatable pathologies and particularly benefited by health laws for their treatment with special products and with so-called orphan drugs, allowing so the access to safe and effective therapies to treat their symptoms and the cause that produces them. Its diagnosis must be clinically suspected in certain signs and symptoms patterns, in addition to simple laboratory analyzes, normally available in all those hospitals that have specialized their Reference Units for the diagnosis, treatment and monitoring of these pathologies. The treatment of this type of diseases should be established to avoid the development of irretrievable sequels. The existence of Neonatal Screening Programs is the ideal diagnostic approach to reach the early diagnosis.

The Inborn Errors of Metabolism (IEM) are manifested in the pediatric age, from the first hours of life, until adolescence or adulthood with symptoms and signs similar to other pathologies. Not recognizing them, leads to sequels such as severe malnutrition, seizures, intellectual disability and even death. The prevention of these sequels with a timely diagnosis is the challenge faced by pediatricians.

Some of the most commonly known Inborn Errors of Metabolism (IEM) are those that directly affect some amino acids metabolism, such as:

PKU (Phenylketonuria)

It is a metabolic disorder by which an organism fails to properly metabolize a specific amino acid due to the absence or deficiency of Phenylalanine Hydroxylase, an enzyme responsible for facilitating the passage of Phenylalanine to Tyrosine. The Phenylalanine, as it has a defective activity, it accumulates and is toxic for the central nervous system, causing irreversible brain damage.

PKU is a genetic, autosomal, recessive disease. That is to say: parents are carriers of the defective genes that when being pierced by both parents, the consequence is the expression of the disease in the progeny.

Thanks to Neonatal Screening, it is easily detectable in newborns and it is estimated that 1 out of every 10,000 live births can present this disease classified as Inborn Error of Amino Acid Metabolism.

The first symptoms of PKU, appear within a few days after birth, they are manifested by an increase of phenylalanine in blood up to 30 times higher than usual and by the excretion of phenylpyruvic acid in urine.

To prevent brain damage, the patient must be early treated and prevent the accumulation of phenylalanine through the modification of the feeding behavior in time, among others. Only in this way, a completely normal development will be achieved.

Usually, a newborn PKU patient does not present any trait or distinctive abnormality when treated opportunely. But those untreated PKUs tend to have light hair, clear and very sensitive skin, blue eyes and short stature.

When a PKU patient follow a strictly restricted diet or limited in high biological value proteins (which is the case) its clinical outcome is very encouraging. But, on the contrary, if the beginning of his treatment is delayed or if the compliance and control of his diet is deficient, the patient will present irreversible brain damage, compromising his future normal development.

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