On the complexity of clinical and molecular bases of neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) is a group of inherited heterogeneous neurodegenerative rare disorders. These patients present with dystonia, spasticity, parkinsonism and neuropsychiatric disturbances, along with brain magnetic resonance imaging (MRI) evidence of iron accumulation. In sum, they are devastating disorders and to date, there is no specific treatment. Ten NBIA genes are accepted: PANK2, PLA2G6, C19orf12, COASY, FA2H, ATP13A2, WDR45, FTL, CP, and DCAF17; and nonetheless, a relevant percentage of patients remain without genetic diagnosis, suggesting that other novel NBIA genes remain to be discovered. Overlapping complex clinical pictures render an accurate differential diagnosis difficult. Little is known about the pathophysiology of NBIAs. The reported NBIA genes take part in a variety of pathways: CoA synthesis, lipid and iron metabolism, autophagy, and membrane remodeling. The next-generation sequencing revolution has achieved relevant advances in genetics of Mendelian diseases and provide new genes for NBIAs, which are investigated according to 2 main strategies: genes involved in disorders with similar phenotype and genes that play a role in a pathway of interest. To achieve an effective therapy for NBIA patients, a better understanding of the biological process underlying disease is crucial, moving toward a new age of precision medicine.

Hypokinetic-rigid syndrome in children and inborn errors of metabolism

Hypokinetic-rigid syndrome (HRS) or "parkinsonism" is rare in children. From a clinical point of view it is characterised by a group of signs in which hypokinesia (decreased number of movements), bradykinesia (slowness of movements), rigidity and rest tremor are the fundamental traits. Nervous system infections, immunomediated encephalitis, hypoxia and some drugs have been described as acquired or secondary causes of HRS in the paediatric age. Inborn errors of metabolism (IEM) comprise and important group regarding genetic causes. Main diseases causing HRS in children are neurotransmitter (biogenic amines) defects, metal storage diseases, energy metabolism disorders and lysosomal diseases. In general, in IEM, the HRS is associated to other neurological signs such as dykinesias, pyramidal signs, and psychomotor delay, is very rare in the neonatal period, tends to be more frequent in advanced stages of progressive diseases, and may respond to specific therapies. In particular, l-dopa + carbidopa can be a very effective treatment in neurotransmitter defects, whereas other disorders such as Wilson disease and some particular lysosomal disorders have different therapeutic possibilities. Furthermore, other genetic conditions in dopa-responsive and non-responsive HRS should be also considered, especially in juvenile parkinsonism. Through this review, a practical orientation for paediatric neurologists concerning clinical clues, diagnostic procedure and treatment of metabolic HRS will be provided.

Ancient origin of the CTH alelle carrying the c.200C>T (p.T67I) variant in patients with cystathioninuria

Hereditary cystathioninuria is due to mutations in the CTH gene that encodes for cystathionase, a pyridoxal-5'-phosphate (PLP) dependent enzyme. To date, mutations in this gene have been described in 10 unrelated cystathioninuric patients. Enzyme assays have showed that mutated cystathionase exhibits lower activity than controls. As cystathioninuria is usually accompanied by a wide variety of symptoms, it has been questioned whether it is a disease or just a biochemical finding not associated with the clinical picture of these patients. This is the first report of Spanish patients with cystathioninuria and mild to severe neurological symptoms in childhood. After oral pyridoxine therapy biochemical parameters have normalized but clinical amelioration was not evident. All patients were homozygotes for the c.200C>T (p.T67I) variant which is the most prevalent inactivating mutation in the CTH gene. To further investigate the history of the alleles carrying the c.200C>T transition in Europe, we also constructed the haplotypes on the CTH locus in our Spanish patients as well as in a clinical series of cystathioninuric patients from the Czech Republic harboring the same nucleotide change. We suggest that the CTH p.T67I substitution could have an ancient common origin, which probably occurred in the Neolithic Era and spread throughout Europe.

Mental retardation and inborn errors of metabolism

In countries where clinical phenylketonuria is detected by newborn screening inborn errors of metabolism are rare causes of isolated mental retardation. There is no international agreement about what type of metabolic tests must be applied in patients with unspecific mental retardation. However, and although infrequent, there are a number of inborn errors of metabolism that can present in this way. Because of the high recurrence risk and the possibility of specific therapies, guidelines need to be developed and adapted to different populations. The application of a universal protocol may result in a low diagnostic performance in individual ethnic populations. Consideration of associated signs (extraneurological manifestations, psychiatric signs, autistic traits, cerebellar dysfunction, epilepsy or dysmorphic traits) greatly improves the diagnostic fulfilment.

Inborn errors of metabolism and motor disturbances in children

Motor disturbances are very common in paediatric neurology. Often families can be reassured that these are just variants of normal development. However, abnormal movements can also be the hallmark of severe brain dysfunction of different and complex origins. This review concentrates on motor disturbances as frequent and important symptoms of inborn errors of metabolism. A structured diagnostic approach is developed taking into account age-dependent physiological developments and pathophysiological responses of gross and fine motor functions. A series of investigations are presented with the primary aim of early diagnosis of treatable conditions. The correct recognition and differentiation of movement disorders (ataxia, rigid akinetic syndrome (Fparkinsonism_), dystonia, athetosis, tremor,and others), spasticity, and neuromuscular disorders, requires profound neurological expertise. A high level of suspicion and close interaction between paediatric neurologists and specialists in inborn errors of metabolism are indispensable to effectively and timely identify patients in whom motor disturbances are the presenting and/or main symptom of an inborn error.

Long-term evolution of eight Spanish patients with CDG type Ia: typical and atypical manifestations

Congenital disorder of glycosylation Ia (CDG-Ia) is a metabolic disease with a broad spectrum of clinical signs, including recently described mild phenotypes. Our aim was to describe the clinical presentation and follow-up of eight CDG-Ia patients highlighting atypical features and aspects of evolution of the disease. CDG diagnosis was confirmed by enzymatic analysis of phosphomannomutase (PMM2) and molecular studies of the PMM2 gene. Four neonates presented with cerebral haemorrhage (1), failure to thrive (2) and non-immune hydrops (1) and a fatal course to death (2); pathological examination of the brain in one case revealed olivopontocerebellar atrophy of prenatal origin. During infancy failure to thrive, coagulopathy and hepatopathy were the most significant causes of morbidity, but these disappeared after the first years of life in most patients. Three patients are currently in their 20s; they present mental retardation and severe motor impairment but no acute decompensations were noticed after the first decade of life. They do not present spinal or thoracic deformities otherwise observed in patients from northern countries. A 10-year-old patient who manifested gastrointestinal dysfunction in early childhood showed normal neurodevelopment. Mutation analysis of the PMM2 gene showed great variability, with all patients being compound heterozygous for two different mutations. Long-term evolution in our patients indicates that CDG-Ia is a stable systemic and neurological condition after the first decade of life. The diverse phenotypes and atypical manifestations in our series may be due to their genetic heterogeneity.

Secondary abnormalities of neurotransmitters in infants with neurological disorders

Neurotransmitters are essential in young children for differentiation and neuronal growth of the developing nervous system. We aimed to identify possible factors related to secondary neurotransmitter abnormalities in pediatric patients with neurological disorders. We analyzed cerebrospinal fluid (CSF) and biogenic amine metabolites in 56 infants (33 males, 23 females; mean age 5.8mo [SD 4.1mo] range 1d-1y) with neurological disorders whose aetiology was initially unknown. Patients were classified into three clinical phenotypes: epileptic encephalopathy, severe motor impairment, and non-specific manifestations. All patients showed normal results for screening of inborn errors of metabolism. We report clinical, neuroimaging, and follow-up data. Among the patients studied, 10 had low homovanillic acid (HVA) levels and in four patients, 5-hydroxyindoleacetic acid (5-HIAA) was also reduced. Patients with neonatal onset had significantly lower levels of HVA than a comparison group. HVA deficiency was also associated with severe motor impairment and the final diagnosis related to neurodegenerative disorders. 5-HIAA values tended to be decreased in patients with brain cortical atrophy. The possibility of treating patients with L-Dopa and 5-hydroxytryptophan, in order to improve their neurological function and maturation, may be considered.

[Orientation of mental retardation from neurometabolic diseases]

INTRODUCTION AND DEVELOPMENT

Isolated mental retardation is rarely caused by metabolic factors. The application of a standardised protocol offers low diagnostic performance. There is no international agreement about what type of metabolic examination must be applied in patients with unspecific mental retardation. Nevertheless, and although they are infrequent, there are a number of inborn errors of metabolism that can present in this way. Urea cycle disorders, different forms of homocystinuria, creatine transport deficiency, 4-hydroxybutyric aciduria, Sanfilippo disease, adenylosuccinate lyase deficit and certain extraordinarily rare congenital disorders of the glycosylation of proteins are some examples of them. It is important first to consider those for which treatment is available and that could be diagnosed genetically for possible family counselling.

CONCLUSIONS

Rather than applying a standardised study protocol it is essential is to perform a thorough appraisal of the signs and symptoms associated with the mental retardation (psychiatric disorders, autistic traits, predominant compromise of language, signs of cerebellar dysfunction, epilepsy, dysmorphic traits), since in most disorders it is necessary to apply specific analyses, which are not included in conventional metabolic studies and are only available in certain reference centres.

Global and regional volume changes in the brains of patients with phenylketonuria

Background: Although phenylketonuria is a treatable disease, patients with late or nonoptimal phenylalanine-restricted diet may experience brain damage. The authors used tridimensional MRI and a voxelwise analysis method to investigate possible volume changes in the brain parenchyma of patients with phenylketonuria.

Methods: The authors assessed 27 treated patients (mean age ± SD, 20 ± 7 years) and 27 matched control subjects. Global tissue volumes were compared, and statistical parametric maps of between-group regional volume differences were obtained for gray and white matter. Anatomic data were correlated with relevant clinical and biochemical variables.

Results: Patients with phenylketonuria showed smaller gray matter volumes that were associated with lower IQ and older age at diagnosis. Voxel-based maps revealed that significant gray matter volume reduction occurred in motor and premotor cortex and thalamus. A relative increase in gray matter volume was observed in the ventral part of the striatum. The authors found no group differences for global white matter measurements. Higher recent phenylalanine levels, however, were associated with larger global white matter volume in early-treated patients. Voxel-based maps showed a relative volume reduction in periventricular white matter and a relative increase in the region of the internal capsule, extending to the adjacent thalamus and striatum.

Conclusions: Treated patients may show significant gray and white matter volume changes related to the duration and strict observation of dietary treatment. Further studies are needed to investigate whether the presence of neurologic symptoms may be explained by specific anatomic alterations.

[Inborn errors of neurotransmitters in neuropaediatrics]

AIMS

The aim of this work is to describe the clinical, biochemical and genetic characteristics of neurotransmitter diseases at the paediatric age, together with possible forms of treatment. We also sought to determine the diagnostic methodology of these disorders (collection and analysis of samples).

DEVELOPMENT

These diseases essentially consist of a deficit of biogenic amines and alterations in GABA metabolism (gamma-aminobutyric acid). Disorders affecting the neurotransmission of biogenic amines often present in the form of hypokinesia, trunk hypotonia with increased limb tone, oculogyric crises, ptosis, faulty temperature regulation or abnormal movements. Defects in GABA metabolism give rise to epileptic encephalopathies and unspecific mental retardation, sometimes associated to signs of cerebellar dysfunction, convulsions and alterations in neuroimaging studies. Overall incidence of these diseases is low but they are unquestionably under-diagnosed, since they cannot be detected by conventional studies in plasma and urine, and require extraction and directed analysis of cerebrospinal fluid (CSF) for their detection. Additionally, the CSF study must be carried out in specific standardised conditions. Segawa's disease, or dopa-responsive dystonia, responds extremely well to therapy, whereas the other entities respond in varying ways to the different therapeutic alternatives.

CONCLUSIONS

It is important for the paediatrician to know about these entities as a group of treatable neurometabolic diseases. Moreover, their detection would allow prenatal diagnosis in the vast majority of cases.

Platelet serotonin concentrations in PKU patients under dietary control and tetrahydrobiopterin treatment

Tetrahydrobiopterin (BH4) supplementation has been applied in PKU treatment, resulting in successful control of blood phenylalanine (Phe) concentrations. We evaluated serotonin status in PKU patients under classical dietary treatment (n = 40) and in a group of 11 PKU patients under BH4 treatment, both during a 6-month period. Platelet serotonin values were significantly lower in PKU patients under dietary treatment when compared with controls. A negative correlation was observed between plasma Phe and platelet serotonin concentrations (r = -0.367, p = 0.017) in PKU patients. Platelet serotonin concentration increased significantly after both 1 and 6 months of BH4 therapy when compared with baseline conditions (Wilcoxon test: p = 0.013 and p = 0.021, respectively), while no differences were observed when comparing plasma Phe concentrations at the different points. Our results indicate that PKU patients under classical treatment have decreased platelet serotonin concentrations, probably owing to continued high Phe values, while BH4 supplementation restored platelet serotonin values.

[Course and treatment of progressive subacute encephalopathy caused by human immunodeficiency virus in children. The value of Botulinum toxin]

INTRODUCTION

Progressive subacute encephalopathy due to human immunodeficiency virus (PSE-HIV) is an important cause of morbidity and mortality in perinatal HIV infection. Although current combined antiretroviral therapies do manage to check its progression, they often give rise to severe motor sequelae that are similar to the spastic infantile cerebral palsy resulting from other aetiologies. We present the case reports of four preschool age children suffering from this pathology who have benefited from long term treatment with botulinum toxin type A (BTA).

CASE REPORTS

Four patients suffering from early onset PSE HIV, who responded well to combined antiviral therapies, and who had severe motor sequelae (two cases of tetraparesis and two spastic dysplegias), with no cognitive disorders. The multidisciplinary treatment of their motor disorder included six monthly sessions of muscular injections of BTA in the usual doses, with good results from the functional point of view and with no significant side effects.

DISCUSSION

PSE-HIV is defined by one of the following criteria: acquired microcephalus, retarded neurological development or symmetrical motor involvement. It constitutes one of the most frequent diagnostic criteria of AIDS in patients infected by vertical transmission. An early diagnosis and treatment are fundamental for the patient's prognosis. Severe motor sequelae in the form of spastic infantile cerebral palsy are frequent. In our experience treatment of the spasticity associated to this entity with BTA has proved to be useful and safe, with a clear improvement in gait functionality.

New approach to osteopenia in phenylketonuric patients

AIM

To study bone mineralization in a group of phenylketonuric patients and to search for a possible relationship between bone mineral density, dietary control, serum minerals and nutrition intake. The response to treatment with low-dose 1.25-(OH)2 vitamin D in patients with osteopenia was evaluated.

METHODS

Twenty-eight phenylketonuric patients (age range: 10-33 y) on dietary treatment were investigated. Bone density at the lumbar spine (Dual Energy X-ray Absorptiometry), bone formation markers (osteocalcin and bone alkaline phosphatase), serum minerals, index of dietary control and protein, vitamin D and mineral intakes were determined.

RESULTS

Of the patients studied, 78.6% had good dietary compliance (462 +/- 89 micromol/L). Mean protein, vitamin D and mineral intakes met the recommended dietary allowances (RDAs). Nevertheless, 8 patients had calcium intakes lower than 1000 g/d, and a positive correlation between Z-score and calcium (r = 0.585; p = 0.002) or phosphorus intake (r = 0.546; p = 0.005) was observed. Osteopenia was detected in 14 patients (50%). Moreover, bone alkaline phosphatase in phenylketonuric patients older than 18 y of age was significantly lower than that in controls (p < 0.0001). No correlation was found between bone mineral density, age, serum minerals, bone formation markers or index of dietary control. Treatment with 0.25 microg/d calcitriol significantly increased bone density in 6 patients.

CONCLUSION

A defect in bone mineralization was detected in 50% of patients in our series. The correct amount of formula intake seems to be necessary for bone mineralization in phenylketonuric patients. Calcitriol can be a useful treatment for these patients, although more studies are needed to confirm these results. Hypercalcaemia and hypercalciuria need to be carefully monitored.