A novel neurodevelopmental syndrome responsive to 5-hydroxytryptophan and carbidopa

Secondary biogenic amine deficiencies: genetic etiology, therapeutic interventions, and clinical effects

Monoamine neurotransmitter disorders present predominantly with neurologic features, including dystonic or dyskinetic cerebral palsy and movement disorders. Genetic conditions that lead to secondary defects in the synthesis, catabolism, transport, and metabolism of biogenic amines can lead to neurotransmitter abnormalities, which can present with similar features. Eleven patients with secondary neurotransmitter abnormalities were enrolled between 2011 and 2015. All patients underwent research-based whole exome and/or whole genome sequencing (WES/WGS). A trial of treatment with levodopa/carbidopa and 5-hydroxytryptophan was initiated. In six families with abnormal neurotransmitter profiles and neurological phenotypes, variants in known disease-causing genes (KCNJ6, SCN2A, CSTB in 2 siblings, NRNX1, KIF1A and PAK3) were identified, while one patient had a variant of uncertain significance in a candidate gene (DLG4) that may explain her phenotype. In 3 patients, no compelling candidate genes were identified. A trial of neurotransmitter replacement therapy led to improvement in motor and behavioral symptoms in all but two patients. The patient with KCNJ6 variant did not respond to L-dopa therapy, but rather experienced increased dyskinetic movements even at low dose of medication. The patient's symptoms harboring the NRNX1 deletion remained unaltered. This study demonstrates the utility of genome-wide sequencing in further understanding the etiology and pathophysiology of neurometabolic conditions, and the potential of secondary neurotransmitter deficiencies to serve as novel therapeutic targets. As there was a largely favorable response to therapy in our case series, a careful trial of neurotransmitter replacement therapy should be considered in patients with cerebrospinal fluid (CSF) monoamines below reference range.

Catatonia in Children and Adolescents: A High Rate of Genetic Conditions

Pediatric catatonia is a rare and severe neuropsychiatric syndrome. We previously reported, in 58 children and adolescents with catatonia, a high prevalence (up to 20%) of medical conditions, some of which have specific treatments.¹ Here we extend the cohort inclusion and report the first systematic molecular genetic data for this syndrome. Among the 89 patients consecutively admitted for catatonia (according to the pediatric catatonia rating scale)² between 1993 and 2014, we identify 51 patients (57.3%) who had genetic laboratory testing, of whom 37 had single nucleotide polymorphism (SNP) microarray tests for CNVs and 14 had routine genetic explorations (karyotyping and searches for specific chromosomal abnormalities by fluorescence in situ hybridization [FISH]) or a specific diagnosis test based on clinical history. To assess the causality of observed genetic findings in each patient, we used a causality assessment score (CAUS)³ including 5 causality-support criteria on a 3-point scale (0 = absent; 1 = moderate; 2 = high): the existence of similar cases in the literature; the presence of a clinical contributing factor; the presence of a biological contributing factor; the presence of other paraclinical symptoms; and response to a specific treatment related to the suspected genetic or medical condition.

Neurodevelopment: The Impact of Nutrition and Inflammation During Preconception and Pregnancy in Low-Resource Settings

The rapid pace of fetal development by far exceeds any other stage of the life span, and thus, environmental influences can profoundly alter the developmental course. Stress during the prenatal period, including malnutrition and inflammation, impact maternal and fetal neurodevelopment with long-term consequences for physical and mental health of both the mother and her child. One primary consequence of maternal malnutrition, inflammation, and other sources of prenatal stress is a poor birth outcome, such as prematurity or growth restriction. These phenotypes are often used as indications of prenatal adversity. In fact, the original evidence supporting the fetal programming hypothesis came from studies documenting an association between birth phenotype and the development of subsequent physical and mental health problems. Fetal growth restriction in both term and preterm infants is associated with neonatal morbidities and a wide variety of behavioral and psychological diagnoses in childhood and adolescence, including attention-deficit/hyperactivity disorder, anxiety, depression, internalizing and thought problems, poor social skills, and autism spectrum disorder. Improving maternal-child health requires interventions that begin before pregnancy and continue throughout gestation and into the postpartum period. Such interventions might include supporting pregnancy intention, maternal nutrition, health/medical care, mental health, and providing social support. This article discusses the impact of maternal nutrition and inflammation during preconception and pregnancy among women living in low-resource settings, with an emphasis on key knowledge gaps that need to be addressed to guide program and policy decisions at local, regional and global levels.

Autism spectrum disorder associated with low serotonin in CSF and mutations in the SLC29A4 plasma membrane monoamine transporter (PMAT) gene

Background

Patients with autism spectrum disorder (ASD) may have low brain serotonin concentrations as reflected by the serotonin end-metabolite 5-hydroxyindolacetic acid (5HIAA) in cerebrospinal fluid (CSF).

Methods

We sequenced the candidate genes SLC6A4 (SERT), SLC29A4 (PMAT), and GCHFR (GFRP), followed by whole exome analysis.

Results

The known heterozygous p.Gly56Ala mutation in the SLC6A4 gene was equally found in the ASD and control populations. Using a genetic candidate gene approach, we identified, in 8 patients of a cohort of 248 with ASD, a high prevalence (3.2%) of three novel heterozygous non-synonymous mutations within the SLC29A4 plasma membrane monoamine transporter (PMAT) gene, c.86A > G (p.Asp29Gly) in two patients, c.412G > A (p.Ala138Thr) in five patients, and c.978 T > G (p.Asp326Glu) in one patient. Genome analysis of unaffected parents confirmed that these PMAT mutations were not de novo but inherited mutations. Upon analyzing over 15,000 normal control chromosomes, only SLC29A4 c.86A > G was found in 23 alleles (0.14%), while neither c.412G > A (<0.007%) nor c.978 T > G (<0.007%) were observed in all chromosomes analyzed, emphasizing the rareness of the three alterations. Expression of mutations PMAT-p.Ala138Thr and p.Asp326Glu in cellulae revealed significant reduced transport uptake activity towards a variety of substrates including serotonin, dopamine, and 1-methyl-4-phenylpyridinium (MPP⁺), while mutation p.Asp29Gly had reduced transport activity only towards MPP⁺. At least two ASD subjects with either the PMAT-Ala138Thr or the PMAT-Asp326Glu mutation with altered serotonin transport activity had, besides low 5HIAA in CSF, elevated serotonin levels in blood and platelets. Moreover, whole exome sequencing revealed additional alterations in these two ASD patients in mainly serotonin-homeostasis genes compared to their non-affected family members.

Conclusions

Our findings link mutations in SLC29A4 to the ASD population although not invariably to low brain serotonin. PMAT dysfunction is speculated to raise serotonin prenatally, exerting a negative feedback inhibition through serotonin receptors on development of serotonin networks and local serotonin synthesis. Exome sequencing of serotonin homeostasis genes in two families illustrated more insight in aberrant serotonin signaling in ASD.

Hemiplegic migraine, seizures, progressive spastic paraparesis, mood disorder, and coma in siblings with low systemic serotonin

Background: Serotonin has an important role in vascular resistance and blood pressure control, and a functional serotonin transporter polymorphism has been associated with migraine. Disturbances in serotonin metabolism have been associated with autism, depression, and myoclonus related conditions, but serotonin has far more functions in the body. Familial hemiplegic migraine is a rare autosomal dominant subtype of migraine with aura in which attacks are associated with hemiparesis.

Cases: We present two siblings with hemiplegic migraine, depression, progressive spastic paraparesis, myelopathy, and spinal cord atrophy. One of the sisters presented with prolonged coma after a migraine episode. Both sisters were found to have low cerebrospinal fluid serotonin metabolite (5-hydroxyindoleacetic acid), low platelet serotonin levels, and diminished serotonin transport capacity. Their clinical symptoms improved on 5-hydroxytryptophan replacement therapy. Mutational analysis of the CACNA1A and ATP1A2 genes was negative.

Conclusion: This is the first time that systemic serotonin deficiency has been described in familial hemiplegic migraine. We hypothesize that the deficiency of serotonin transport may be part of a complex cellular membrane trafficking dysfunction involving not only the serotonin transporter but also other transporters and ion channels.

Cerebrospinal fluid alterations of the serotonin product, 5-hydroxyindolacetic acid, in neurological disorders

Although patients with low cerebrospinal fluid (CSF) serotonin metabolite levels have been reported, inborn errors of the rate-limiting enzyme of serotonin synthesis (tryptophan hydroxylase, TPH) have not been described so far. In this study we aimed to evaluate CSF alterations of the serotonin metabolite 5-hydroxyindolacetic acid (5-HIAA) in patients with neurological disorders and to explore a possible TPH deficiency in some of them. A total of 606 patients (286 males, 320 females, mean age 4 years and 6 months, SD 5 years and 7 months) underwent CSF analysis of neurotransmitter metabolites by reverse phase high performance liquid chromatography. Results were compared with values established in a control population. Patients' medical records were reviewed to determine diagnosis and clinical features. A primary defect of biogenic amines was genetically investigated in indicated patients. Low 5-HIAA was seen in 19.3%. Of these, 22.2% showed inborn errors of metabolism (mitochondrial disorders being the most frequent at 10.2% of low 5-HIAA patients) and neurogenetic conditions. Other relatively frequent conditions were pontocerebellar hypoplasia (4.3%), Rett syndrome (4.3%), and among congenital nonetiologically determined conditions, epilepsy including epileptic encephalopathies (26.4%), leukodystrophies (6.8%), and neuropsychiatric disturbances (4.2%). Mutational analysis of the TPH2 gene, performed in five candidate patients, was negative. Although frequency of secondary alteration of 5-HIAA was relatively high in patients with neurological disorders, this finding was more frequently associated with some neurometabolic disorders, epileptic encephalopathies, and neuropsychiatric disturbances. No inborn errors of TPH were found. Due to serotonin's neurotrophic role and to ameliorate symptoms, a supplementary treatment with 5-hydroxytriptophan would seem advisable in these patients.

Mutations in human monoamine-related neurotransmitter pathway genes

Biosynthesis and metabolism of serotonin and catecholamines involve at least eight individual enzymes that are mainly expressed in tissues derived from the neuroectoderm, e.g., the central nervous system (CNS), pineal gland, adrenal medulla, enterochromaffin tissue, sympathetic nerves, and ganglia. Some of the enzymes appear to have additional biological functions and are also expressed in the heart and various other internal organs. The biosynthetic enzymes are tyrosine hydroxylase (TH), tryptophan hydroxylases type 1 and 2 (TPH1, TPH2), aromatic amino acid decarboxylase (AADC), dopamine beta-hydroxylase (DbetaH), and phenylethanolamine N-methyltransferase (PNMT), and the specific catabolic enzymes are monoamine oxidase A (MAO-A) and catechol O-methyltransferase (COMT). For the TH, DDC, DBH, and MAOA genes, many single nucleotide polymorphisms (SNPs) with unknown function, and small but increasing numbers of cases with autosomal recessive mutations have been recognized. For the remaining genes (TPH1, TPH2, PNMT, and COMT) several different genetic markers have been suggested to be associated with regulation of mood, pain perception, and aggression, as well as psychiatric disturbances such as schizophrenia, depression, suicidality, and attention deficit/hyperactivity disorder. The genetic markers may either have a functional role of their own, or be closely linked to other unknown functional variants. In the future, molecular testing may become important for the diagnosis of such conditions. Here we present an overview on mutations and polymorphisms in the group of genes encoding monoamine neurotransmitter metabolizing enzymes. At the same time we propose a unified nomenclature for the nucleic acid aberrations in these genes. New variations or details on mutations will be updated in the Pediatric Neurotransmitter Disorder Data Base (PNDDB) database (www.bioPKU.org).

HPLC with electrochemical and fluorescence detection procedures for the diagnosis of inborn errors of biogenic amines and pterins

The analysis of biogenic amines (BA) and pterins in cerebrospinal fluid (CSF) is essential for the early diagnosis of neurotransmission defects in the paediatric age. Our aim was to standardize previously reported HPLC procedures for the analysis of BA and pterins in CSF and to establish reference values for a paediatric population. Samples from 127 subjects (age range 11 days to 16 years; average 3.8) were analyzed by HPLC with electrochemical and fluorescence detection. Both BA (homovanilic and 5-hydroxyindoleacetic acid) and pterins (neopterin and biopterin) concentrations in CSF showed a negative correlation with age. This finding led us to stratify reference values into six groups according to age. In conclusion, analysis of BA and pterins in CSF by HPLC procedures is a useful set of tools for the diagnosis of inborn errors of metabolism of these compounds. The establishment of reference intervals may be difficult, since there is a strong correlation between BA concentrations and the age of controls and, as a result, a large number of CSF samples from control populations would be necessary for this purpose.

Impairments in working memory associated with naturalistic dieting in women: no relationship between task performance and urinary 5-HIAA levels

The present study investigated the question of whether the previously observed impairments of working memory characteristic of dieting to lose weight can be explained in terms of preoccupying cognitions relating to body shape or to alterations in serotonergic function resulting from a low dietary intake of tryptophan. The population comprised female non-dieting, lower restrained eaters (N=23), non-dieting higher restrained eaters (N=11) and current dieters (N=19). Each participant completed three tasks, each of which selectively loaded on to a different sub-component of working memory. The tasks comprised the Tower of London task, a letter string recall task and a mental rotation task. In addition, all participants completed self-report measures of body shape concern and affective state. Serotonin turnover was assessed by means of 24 h urine sample collection for each participant on their day of testing. This was analysed (via HPLC) for levels of the main serotonin metabolite 5-HIAA.The results of the present study broadly replicated previous findings of a Central Executive and Phonological Loop (but not Visuo-Spatial Sketchpad) deficit in those subjects who reported themselves to be currently dieting. Tower of London task performance also significantly correlated with self-reported feelings of fatness and body shape disparagement. There were no group differences in 5-HIAA levels nor did 5-HIAA levels correlate with task performance. However, there was a significant negative correlation between 5-HIAA levels and self-reported depression. These results support the hypothesis that the variables mediating this deficit are preoccupying cognitions concerning body shape. They do not support the hypothesis that the serotonergic function of dieters is compromised, although this conclusion is tentative.

Diagnosis and treatment of neurotransmitter-related disorders

Neurotransmitter disorders constitute a spectrum of neurologic conditions that share several clinical features depending on the severity and pattern of neurotransmitter deficiency or excess. These uncommon conditions can be suspected based on their clinical features, and several can be confirmed by cerebrospinal fluid analysis of neurotransmitters and their metabolites. Certain disorders, such as autosomal dominant dopa-responsive dystonia caused by GTP cyclohydrolase deficiency, or Segawa syndrome, respond dramatically to medical therapy. This article summarizes current knowledge regarding the clinical manifestations, diagnosis, and treatment of these important disorders.