The child is neither an adult miniature nor an immature human being: at each age, it expresses specific abilities that optimize adaptation to its environment and development of new acquisitions. Diseases in children cover all specialties encountered in adulthood, and neurology involves a particularly large area, ranging from the brain to the striated muscle, the generation and functioning of which require half the genes of the whole genome and a majority of mitochondrial ones. Human being nervous system is sensitive to prenatal aggression, is particularly immature at birth and development may be affected by a whole range of age-dependent disorders distinct from those that occur in adults. Even diseases more often encountered in adulthood than childhood may have specific expression in the developing nervous system. The course of chronic neurological diseases beginning before adolescence remains distinct from that of adult pathology – not only from the cognitive but also motor perspective, right into adulthood, and a whole area is developing for adult neurologists to care for these children with persisting neurological diseases when they become adults. Just as pediatric neurology evolved as an identified specialty as the volume and complexity of data became too much for the general pediatician or the adult neurologist to master, the discipline has now continued to evolve into so many subspecialties, such as epilepsy, neuromuscular disease, stroke, malformations, neonatal neurology, metabolic diseases, etc., that the general pediatric neurologist no longer can reasonably possess in-depth expertise in all areas, particularly in dealing with complex cases. Subspecialty expertise thus is provided to some trainees through fellowship programmes following a general pediatric neurology residency and many of these fellowships include training in research. Since the infectious context, the genetic background and medical practice vary throughout the world, this diversity needs to be represented in a pediatric neurology textbook. Taken together, and although brain malformations (H. Sarnat & P. Curatolo, 2007) and oncology (W. Grisold & R. Soffietti) are covered in detail in other volumes of the same series and therefore only briefly addressed here, these considerations justify the number of volumes, and the number of authors who contributed from all over the world. Experts in the different subspecialties also contributed to design the general framework and contents of the book. Special emphasis is given to the developmental aspect, and normal development is reminded whenever needed – brain, muscle and the immune system. The course of chronic diseases into adulthood and ethical issues specific to the developing nervous system are also addressed. - A volume in the Handbook of Clinical Neurology series, which has an unparalleled reputation as the world's most comprehensive source of information in neurology - International list of contributors including the leading workers in the field - Describes the advances which have occurred in clinical neurology and the neurosciences, their impact on the understanding of neurological disorders and on patient care

Critical illness polyneuropathy and critical illness myopathy are well recognized in adults, in whom they commonly cause generalized weakness and muscle wasting, with failure to wean from mechanical ventilation. There is significant clinical and neurophysiological overlap between the two conditions. Critical illness polyneuropathy and critical illness myopathy can cause significant morbidity in critically ill children, but they have only occasionally been reported in childhood, and little is known of their prevalence or clinical significance in this population. These conditions seem to be clinically and electrophysiologically similar in children and adults, but prospective studies of these entities are required to better characterize their frequency, natural history, and clinical significance in pediatric practice.

The purines are a group of molecules used by all cells for many vital biochemical processes including energy-requiring enzymatic reactions, cofactor-requiring reactions, synthesis of DNA or RNA, signaling pathways within and between cells, and other processes. Defects in some of the enzymes of purine metabolism are known to be associated with specific clinical disorders, and neurological problems may be a presenting sign or the predominant clinical problem for several of them. This chapter describes three disorders for which the clinical features and metabolic basis are well characterized. Deficiency of adenylosuccinate-lyase (ADSL) causes psychomotor retardation, epilepsy, and autistic features. Lesch–Nyhan disease is caused by deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT) and is characterized by hyperuricemia, motor and cognitive disability, and self-injurious behavior. Deficiency of myoadenylate deaminase (mAMPD) is associated with myopathic features. In addition to these disorders, several other disorders are briefly summarized. These include defects of phosphoribosylpyrophosphate synthase, adenosine deaminase (ADA), purine nucleoside phosphorylase (PND), deoxyguanosine kinase (dGK), or IMP dehydrogenase (IMPDH). Each of these disorders provides an unusual window on the unique importance of purine metabolism for function of different parts of the nervous system.

Symptoms in patients with defects in amino acid catabolism and the urea cycle usually develop because of intoxication of accumulating metabolites. The cumulative prevalence of these disorders is considerable (at least>1:2000 newborns). Timely and correct intervention during the initial presentation and during later episodes is most important. Evaluation of metabolic parameters should be performed on an emergency basis in every patient with symptoms of unexplained metabolic crisis, intoxication, and/or unexplained encephalopathy. A substantial number of patients develop acute encephalopathy or chronic and fluctuating progressive neurological disease. The so-called cerebral organic acid disorders present with (progressive) neurological symptoms: ataxia, myoclonus, extrapyramidal symptoms, and “metabolic stroke.” Important diagnostic clues, such as white matter abnormalities, cortical or cerebellar atrophy, and injury of the basal ganglia can be derived from cranial magnetic resonance imaging (MRI). Long-term neurological disease is common, particularly in untreated patients, and the manifestations are varied, the most frequent being (1) mental defect, (2) epilepsy, and (3) movement disorders. Successful treatment strategies are becoming increasingly available. They mostly require an experienced interdisciplinary team including a neuropediatrician and/or later on a neurologist.

The lack of creatine in the central nervous system causes a severe but treatable neurological disease. Three inherited defects, AGAT, GAMT, and CrT deficiency, compromising synthesis and transport of creatine have been discovered recently. Together these so-called creatine deficiency syndromes (CDS) might represent the most frequent metabolic disorders with a primarily neurological phenotype. Patients with CDS present with global developmental delays, mental retardation, speech impairment especially affecting active language, seizures, extrapyramidal movement disorder, and autism spectrum disorder. The two defects in the creatine synthesis, AGAT and GAMT, are autosomal recessive disorders. They can be diagnosed by analysis of the creatine, guanidinoacetate, and creatinine in body fluids. Treatment is available and, especially when introduced in infancy, has a good outcome. The defect of creatine transport, CrT, is an X-linked condition and perhaps the most frequent reasons for X-linked mental retardation. Diagnosis is made by an increased ratio of creatine to creatinine in urine, but successful treatment still needs to be explored. CDS are under-diagnosed because easy to miss in standard diagnostic workup. Because CDS represent a frequent cause of cognitive and neurological impairment that is treatable they warrant consideration in the workup for genetic mental retardation syndromes, for intractable seizure disorders, and for neurological diseases with a predominant lack of active speech.

Inborn errors of metabolism may present with acute neurological symptoms at any age. However, especially in neonates and infants, these conditions may be acute and if untreated may lead to permanent cerebral lesions or to death. Knowledge of the main signs and symptoms of these conditions may be lifesaving, especially for conditions that are treatable. From the pathophysiological perspective, errors of metabolism can be divided into disorders causing “intoxication,” disorders impairing energy production, and disorders involving complex molecules. From the clinical perspective, errors of metabolism may present with acute symptoms in the neonatal period and early infancy; late-onset acute and recurrent attacks; chronic and progressive symptoms. Nonspecific readily available biochemical markers may suggest the underlying condition but in most cases the choice of appropriate biochemical and molecular tests is required to establish the diagnosis. Progress in the treatment of inborn errors of metabolism has been slower than progress in diagnostic methods and in understanding of the pathophysiology of these disorders. Nevertheless, outcomes are improving with the use of dialysis and drugs to promote the removal of toxic metabolites and measures to keep catabolism to a minimum. Early intervention is crucial when neurological sequelae could be avoided, which requires constant vigilance and routine measurement of diagnostic biochemical markers in suspected cases.

The Niemann–Pick disease group is now divided into two distinct entities: (1) acid sphingomyelinase-deficient Niemann–Pick disease (ASM-deficient NPD) resulting from mutations in the SMPD1 gene and encompassing type A and type B as well as intermediate forms; (2) Niemann–Pick disease type C (NP-C) including also type D, resulting from mutations in either the NPC1 or the NPC2 gene. Both Niemann–Pick diseases have an autosomal recessive inheritance and are lysosomal lipid storage disorders, with visceral (type B) or neurovisceral manifestations. The clinical knowledge is updated taking into account recent surveys in large cohort of patients, particularly for type B and type C. The diagnosis of NP-C is often delayed due to the wide spectrum of clinical phenotypes. Systemic manifestations, if present, always precede onset of neurological manifestations. Most common neurological signs are vertical supranuclear gaze palsy, cerebellar ataxia, dysarthria, dysphagia, and progressive dementia. Cataplexy, seizures, and dystonia are other common features of NP-C. For both ASM-deficient NPD and NP-C, strategies for laboratory diagnosis of patients and prenatal diagnosis are discussed. Recent progress towards enzyme replacement therapy in type B patients and management of the neurological disease in type C patients are finally highlighted.

Defects in the synthesis pathways of amino acids have only been discovered in recent years and are relatively unknown to most clinicians. In this chapter disorders neurological symptoms caused by genetic defects in the synthesis of the amino acids serine, glutamine and proline are discussed. Patients with serine deficiency invariably suffer from severe neurological symptoms such as microcephaly, psychomotor retardation and intractable seizures. The same is true for patients with a defect in the synthesis of glutamine who present with hypotonia and epileptic encephalopathy. Patients with a disorder in the synthesis proline have mental retardation in combination with symptoms of connective tissue disease. All amino acids synthesis disorders, except for one of the proline defects, can be diagnosed by routine amino acid analysis. Given the fact that the disorder discussed here lead to deficiencies of amino acids opens up possibilities to treat these patients with the amino acids that can’t be synthesised. Prompt recognition and treatment of amino acid synthesis disorders are of outmost importance to obtain satisfactory treatment results.

We review the clinical examination of the optic disc and assessment of the integrity of the visual pathways: assessment of vision in the infant and child, assessment of disc size and configuration, detection of abnormalities such as cupping or disc swelling and their significance, visual field examination in the child, and the various field defects which result from pathology affecting the visual pathway anywhere along its course. Congenital anomalies of the optic disc, their systemic associations and significance are discussed. We also review the presentation of the visually impaired child, the significance of nystagmus in this context, the differential diagnosis and investigation.

The catalytic properties of many enzymes depend on the participation of vitamins as obligatory cofactors. Vitamin B12 (cobalamin) and folic acid (folate) deficiencies in infants and children classically present with megaloblastic anemia and are often accompanied by neurological signs. A number of rare inborn errors of cobalamin and folate absorption, transport, cellular uptake, and intracellular metabolism have been delineated and identification of disease-causing mutations has improved our ability to diagnose and treat many of these conditions. Two inherited defects in biotin metabolism are known, holocarboxylase synthetase and biotinidase deficiency. Both lead to multiple carboxylase deficiency manifesting with metabolic acidosis, neurological abnormalities, and skin rash. Thiamine-responsive megaloblastic anemia is characterized by megaloblastic anemia, non-type I diabetes, and sensorineural deafness that responds to pharmacological doses of thiamine (vitamin B1). Individuals affected with inherited vitamin E deficiencies including ataxia with isolated vitamin E deficiency and abetalipoproteinemia present with a spinocerebellar syndrome similar to patients with Friedreich's ataxia. If started early, treatment of these defects by oral or parenteral administration of the relevant vitamin often results in correction of the metabolic defect and reversal of the signs of disease, stressing the importance of early and correct diagnosis in these treatable conditions.