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Phenylketonuria, also known as PKU, is the most frequent congenital inborn error of metabolism. The severe form or classic PKU untreated causes intellectual disability, although with the early detection programs in the neonatal period, diagnosis and treatment prevent the appearance of the symptoms. Despite early diagnosis and treatment we have observed some neurotoxicity in treated PKU patients. We analyzed the factors involved apart from the toxicity due to the high cerebral concentrations of phenylalanine (Phe), the defects of synthesis of neurotransmitters, the alteration of cerebral myelination, the effect of the elevation of Phe in the processes of transport and distribution of neutral amino acids with an abnormal synthesis of brain proteins, plasma and cerebral tyrosine deficiency, the neurotoxicity of Phe metabolites, the defect of cholesterol biosynthesis or the increase of oxidative stress. White matter alterations in early treated PKU patients have an important role in neurological manifestations. The treatment of PKU is for life and is based on the reduction of foods containing Phe combined with the administration of a special formula or tetrahydrobiopterin (BH4) treatment. New therapeutic options will be analyzed.La fenilcetonuria, también conocida como PKU, es el error congénito más frecuente del metabolismo de los aminoácidos. La forma grave o PKU clásica no tratada, causa una discapacidad intelectual, aunque los programas de detección en el período neonatal, el diagnóstico y el tratamiento evitan la aparición de los síntomas. A pesar de un diagnóstico y tratamiento temprano hemos observado cierta neurotoxicidad en los pacientes con PKU tratados. Analizamos los demás factores implicados, aparte de la toxicidad por las elevadas concentraciones cerebrales de fenilalanina (Phe), se revisan los defectos de síntesis de neurotransmisores, las alteración de la mielinización cerebral, el efecto de la elevación de Phe en los procesos de transporte y distribución de los aminoácidos neutros con una síntesis anómala de proteínas cerebrales, la deficiencia plasmática y cerebral de tirosina, la neurotoxicidad de los metabolitos de Phe, el defecto de la biosíntesis del colesterol o el aumento del estrés oxidativo. Las alteraciones de la sustancia blanca en los pacientes con PKU tienen un papel importante en las manifestaciones neurológicas. El tratamiento de la PKU es para toda la vida y se basa en la reducción del aporte de alimentos que contienen Phe combinado con la administración de una fórmula especial, o en el tratamiento con tetrahidrobiopterina (BH4). Se analizan nuevas opciones terapéuticas.

Non-epileptic paroxysmal disorders (PNED) are defined as events that mimic epileptic seizures. Its onset is usually sudden and short-lived, caused by brain dysfunction of various origins, but not due to excessive neuronal firing. Its incidence is higher than the epilepsy (10:1). They can occur at any age but are most common in children, especially in the first year of life. The immature nervous system in childhood causes in this period, paroxysmal manifestations that are very diverse and different from other ages. Normal and common paroxysmal disorders in children can mimic epileptic seizures. The first step is to establish a correct diagnosis, if the clinical paroxysmal episode is a seizure or PNED. Differential diagnosis is very broad, especially in the first ages. It's necessary a complete neurological examination in case of doubt and the study should be extended with complementary exams, investigations that in most cases will be normal/negative. In some of them, a genetic basis has been shown. Treatment options are limited and most PNED untreated have a favorable outcome.

Neurometabolic disorders constitute an expanding and complex field in which it is difficult to diagnose and to acquire a specific education and training. This article tries to develop a practical orientation in the suspicion, clinical exam, biochemical studies and neuroimaging techniques for the detection of inborn errors of metabolism. It is very important for the neuropediatrician to suspect metabolic diseases depending on some of the most frequent unexplained neurological disturbances and symptoms as psychomotor delay, mental retardation, refractory epilepsy, dystonia, metabolic crisis or other extraneurological signs. It is important the diagnosis related to the new emergent therapeutic options, genetic counseling and prenatal diagnosis.

Convulsions appearing in the neonatal or first year of life can have a very different origin, treatment or prognosis and it shall be up to the neonatologist or neuropediatrician to resolve the problem since they are the ones who know their patients best. There are severe forms of epileptic encephalopathy in the neonatal period such as Ohtahara syndrome or Aicardi myoclonic encephalopathy with poor prognosis and high morbimortality. Furthermore, there are forms of convulsions and epilepsies during the neonatal and infant period which do not respond to AED. In such cases, it is important to initiate as soon as possible another type of treatment to prevent a neurological deterioration due to repeated convulsion crises and thus allow the patients to lead a normal life with the only obligation to take a different medication from AED during their whole life. We discuss the metabolic defects which lead to convulsions and epilepsies and their various treatments. We also include a revision of some forms of convulsions and epilepsies in the infant insisting on treatments with substances completely different from AEDs.

Congenital metabolic diseases are considered as rare diseases because of their low incidence and their clinical symptoms at onset. Sometimes they can just begin in the neonatal period. Their progressive knowledge and the availability of specific and sensitive biochemical procedures allow us to diagnose many congenital metabolic diseases, which were not recognized some years ago. We reviewed the 52 patients with congenital metabolic diseases diagnosed during the last 25 years in our centre, evaluating the clinical presentation, neurological symptoms, complementary exams and clinical evolution. The mean age at onset of symptoms was 5 days and the mean age at diagnosis was 88 days of age. We considered a first group of 36 patients with inborn errors of intermediary metabolism, in whom hypotonia, weight loss and seizures are the main symptoms. The second group was composed of 8 patients with defective energy metabolism, who showed abnormal respiratory rhythm and hypotonia. Finally, we considered 8 patients with diseases of the complex molecules, who presented with hypotonia and cataracts as common symptoms at onset. The more common neurological symptoms in this period were hypotonia (60%), sensorial deficit (35%) and refractory seizures (23%). The complementary laboratory tests in the first phases of the diseases allowed us to suspect a congenital metabolic disease especially among intermediary and energy defects. EEG and CSF samples were important to diagnose some inborn errors of intermediary metabolism. In the first steps, the neuroimaging was less orientative, even if it allow the exclusion of other diseases. More than half of the patients with inborn errors of metabolism with onset in the neonatal period died within the first two years of life. It is really important to suspect these diseases in the neonatal period so as to achieve an early diagnosis and prompt therapy, specially with cofactors, that can reduce the morbimortality.