A female case of aromatic l-amino acid decarboxylase deficiency responsive to MAO-B inhibition

Aromatic L-Amino Acid Decarboxylase Deficiency: A Genetic Screening in Sicilian Patients with Neurological Disorders

Aromatic L-amino acid decarboxylase deficiency (AADCd) is a rare autosomal recessive neurometabolic disorder caused by AADC deficiency, an enzyme encoded by the DDC gene. Since the enzyme is involved in the biosynthesis of serotonin and dopamine, its deficiency determines the lack of these neurotransmitters, but also of norepinephrine and epinephrine. Onset is early and the key signs are hypotonia, movement disorders (oculogyric crises, dystonia and hypokinesia), developmental delay and autonomic dysfunction. Taiwan is the site of a potential founder variant (IVS6+4A>T) with a predicted incidence of 1/32,000 births, while only 261 patients with this deficit have been described worldwide. Actually, the number of affected persons could be greater, given that the spectrum of clinical manifestations is broad and still little known. In our study we selected 350 unrelated patients presenting with different neurological disorders including heterogeneous neuromuscular disorders, cognitive deficit, behavioral disorders and autism spectrum disorder, for which the underlying etiology had not yet been identified. Molecular investigation of the DDC gene was carried out with the aim of identifying affected patients and/or carriers. Our study shows a high frequency of carriers (2.57%) in Sicilian subjects with neurological deficits, with a higher concentration in northern and eastern Sicily. Assuming these data as representative of the general Sicilian population, the risk may be comparable to some rare diseases included in the newborn screening programs such as spinal muscular atrophy, cystic fibrosis and phenylketonuria.

Burden and severity of disease of aromatic L-amino acid decarboxylase deficiency: a systematic literature review

OBJECTIVE

The objective was to investigate the severity of aromatic L-amino acid decarboxylase deficiency (AADCd) as reported in the published literature and to collate evidence of the clinical manifestations of AADCd, and the impact of the disease on patients, caregivers, and healthcare systems.

METHODS

Published articles reporting severity of disease or disease impact were eligible for inclusion in this review. Articles were searched in MEDLINE, EMBASE, Cochrane CENTRAL, TRIP medical, and CRD databases in October 2021. The quality of the included studies was investigated using a modified version of the grading system of the Centre for Evidence-Based Medicine (CEBM). Descriptive data of the literature was extracted and a narrative synthesis of the results across studies was conducted. This review is reported according to the PRISMA reporting guidelines for systematic reviews.

RESULTS

The search identified 970 unique reports, of which 59 met eligibility criteria to be included in the review. Of these, 48 included reports provided details on the clinical manifestations of AADCd. Two reports explored the disease impact on patients, while four described the impact on caregivers. Five reports assessed the impact on healthcare systems. Individuals with AADCd experience very severe clinical manifestations regardless of motor milestones achieved, and present with a spectrum of other complications. Individuals with AADCd present with very limited function, which, in combination with additional complications, substantially impact the quality-of-life of individuals and their caregivers. The five studies which explore the impact on the healthcare system reported that adequate care of individuals with AADCd requires a vast array of medical services and supportive therapies.

CONCLUSIONS

Irrespective of the ambulatory status of individuals, AADCd is a debilitating disease that significantly impacts quality-of-life for individuals and caregivers. It impacts the healthcare system due to the need for complex coordinated activities of a multidisciplinary specialist team.

Clinical Features in Aromatic L-Amino Acid Decarboxylase (AADC) Deficiency: A Systematic Review

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare congenital autosomal recessive metabolic disorder caused by pathogenic homozygous or compound heterozygous variants in the dopa decarboxylase (DDC) gene. Adeno-associated viral vector-mediated gene transfer of the human AADC gene into the putamina has become available. This systematic review on PubMed, Scopus databases, and other sources is aimed at describing the AADC whole phenotypic spectrum in order to facilitate its early diagnosis. Literature reviews, original articles, retrospective and comparative studies, large case series, case reports, and short communications were considered. A database was set up using Microsoft Excel to collect clinical, molecular, biochemical, and therapeutic data. By analysing 261 patients from 41 papers with molecular and/or biochemical diagnosis of AADC deficiency for which individuality could be determined with certainty, we found symptom onset to occur in the first 6 months of life in 93% of cases. Hypotonia and developmental delay are cardinal signs, reported as present in 73.9% and 72% of cases, respectively. Oculogyric crises were seen in 67% of patients while hypokinesia in 42% and ptosis in 26%. Dysautonomic features have been revealed in 53% and gastrointestinal symptoms in 19% of cases. With 37% and 30% of patients reported being affected by sleep and behavioural disorders, it seems to be commoner than previously acknowledged. Although reporting bias cannot be excluded, there is still a need for comprehensive clinical descriptions of symptoms at onset and during follow-up. In fact, our review suggests that most of the neurological and extraneurological symptoms and signs reported, although quite frequent in this condition, are not pathognomonic, and therefore, ADCC deficiency can remain an underdiscovered disorder.

The genetic and clinical characteristics of aromatic L-amino acid decarboxylase deficiency in mainland China

Aromatic L-amino acid decarboxylase deficiency (AADCD) is a rare neurotransmitter metabolic disorder caused by DDC gene mutations, which leads to the metabolic disturbance of dopamine and serotonin. Most of the reported cases came from Taiwan China, but patients from mainland China were seldomly reported. The current study was the largest AADCD patient cohort from mainland China. Twenty-three patients with clinical features of AADCD and DDC gene variants were recruited. A total of 16 DDC variants were identified in this study, of which four variants (c.2T>C, c.277A>G, c.1021+1G>A, c.565G>T) were never reported previously. The intronic variant c.714+4A>T was the most common one, with an allele frequency of 45.7%. And patients carried this intronic variant presented with severe clinical manifestations, all of whom were bedridden. In this study, the average onset age was 3.61 ± 1.28 months and the average age of diagnosis was 12.91 ± 5.62 months. Early onset hypotonia, oculogyric crises, and autonomic symptoms such as excessive sweating, nasal congestion and profuse nasal, and oropharyngeal secretions, were common in our patients. Eighteen patients (78.3%) got various degree of improvement after using pyridoxine monotherapy or different combination of pyridoxine, dopamine agonists, and monoamine oxidase (MAO) inhibitors.

Aromatic L-amino acid decarboxylase deficiency in 17 Mainland China patients: Clinical phenotype, molecular spectrum, and therapy overview

Background

Aromatic L‐amino acid decarboxylase deficiency (AADCD) is a rare, autosomal recessive inherited disorder which is characterized by neurological and vegetative symptoms. To date, only 130 patients with AADCD have been reported worldwide.

Methods

We demonstrated 14 previously undescribed patients together with three reportedly patients in Mainland China. Full clinical information was collected, and disease‐causing variants in the DDC gene were detected.

Results

The common clinical manifestation of patients, including intermittent oculogyric crises, retarded movement development, and autonomic symptoms. Notably, a patient showed bone‐density loss which have not been reported and two mildly phenotype patients improved psychomotor function after being prescribed medication. The most common genotype of Mainland Chinese AADCD is the splice‐site variant (IVS6+4A> T; c.714+4A> T), which accounts for 58.8%, followed by c.1234C>T variant. Three novel compound heterozygous variants, c. 565G>T, c.170T>C, and c.1021+1G>A, were firstly reported. It is important to recognize the milder phenotypes of the disease as these patients might respond well to therapy. Besides, we discovered that patients may presented with milder if found to be compound heterozygote or homozygote for one of the following variants c.478C>G, c.853C>T, c.1123C>T, c.387G>A, and c.665T>C.

Discussion

The clinical data of the cohort of 17 patients in Mainland China broaden the clinical, molecular, and treatment spectrum of aromatic L‐amino acid decarboxylase deficiency.

Gene therapy improves motor and mental function of aromatic l-amino acid decarboxylase deficiency

In patients with aromatic l-amino acid decarboxylase (AADC) deficiency, a decrease in catecholamines and serotonin levels in the brain leads to developmental delay and movement disorders. The beneficial effects of gene therapy in patients from 1 to 8 years of age with homogeneous severity of disease have been reported from Taiwan. We conducted an open-label phase 1/2 study of population including adolescent patients with different degrees of severity. Six patients were enrolled: four males (ages 4, 10, 15 and 19 years) and one female (age 12 years) with a severe phenotype who were not capable of voluntary movement or speech, and one female (age 5 years) with a moderate phenotype who could walk with support. The patients received a total of 2 × 10¹¹ vector genomes of adeno-associated virus vector harbouring DDC via bilateral intraputaminal infusions. At up to 2 years after gene therapy, the motor function was remarkably improved in all patients. Three patients with the severe phenotype were able to stand with support, and one patient could walk with a walker, while the patient with the moderate phenotype could run and ride a bicycle. This moderate-phenotype patient also showed improvement in her mental function, being able to converse fluently and perform simple arithmetic. Dystonia disappeared and oculogyric crisis was markedly decreased in all patients. The patients exhibited transient choreic dyskinesia for a couple of months, but no adverse events caused by vector were observed. PET with 6-[¹⁸F]fluoro-l-m-tyrosine, a specific tracer for AADC, showed a persistently increased uptake in the broad areas of the putamen. In our study, older patients (>8 years of age) also showed improvement, although treatment was more effective in younger patients. The genetic background of our patients was heterogeneous, and some patients suspected of having remnant enzyme activity showed better improvement than the Taiwanese patients. In addition to the alleviation of motor symptoms, the cognitive and verbal functions were improved in a patient with the moderate phenotype. The restoration of dopamine synthesis in the putamen via gene transfer provides transformative medical benefit across all patient ages, genotypes, and disease severities included in this study, with the most pronounced improvements noted in moderate patients.

Trace Amines and Their Receptors

Trace amines are endogenous compounds classically regarded as comprising β-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs and can be produced and degraded by the constitutive microbiota. The ability to use trace amines has arisen at least twice during evolution, with distinct receptor families present in invertebrates and vertebrates. The term "trace amine" was coined to reflect the low tissue levels in mammals; however, invertebrates have relatively high levels where they function like mammalian adrenergic systems, involved in "fight-or-flight" responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAARs). Humans possess six functional isoforms (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9), whereas some fish species express over 100. With the exception of TAAR1, TAARs are expressed in olfactory epithelium neurons, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system, TAAR1 is the most thoroughly studied and has both central and peripheral roles. In the brain, TAAR1 acts as a rheostat of dopaminergic, glutamatergic, and serotonergic neurotransmission and has been identified as a novel therapeutic target for schizophrenia, depression, and addiction. In the periphery, TAAR1 regulates nutrient-induced hormone secretion, suggesting its potential as a novel therapeutic target for diabetes and obesity. TAAR1 may also regulate immune responses by regulating leukocyte differentiation and activation. This article provides a comprehensive review of the current state of knowledge of the evolution, physiologic functions, pharmacology, molecular mechanisms, and therapeutic potential of trace amines and their receptors in vertebrates and invertebrates.

Eye movement disorders and neurological symptoms in late-onset inborn errors of metabolism

Inborn errors of metabolism in adults are still largely unexplored. Despite the fact that adult‐onset phenotypes have been known for many years, little attention is given to these disorders in neurological practice. The adult‐onset presentation differs from childhood‐onset phenotypes, often leading to considerable diagnostic delay. The identification of these patients at the earliest stage of disease is important, given that early treatment may prevent or lessen further brain damage. Neurological and psychiatric symptoms occur more frequently in adult forms. Abnormalities of eye movements are also common and can be the presenting sign. Eye movement disorders can be classified as central or peripheral. Central forms are frequently observed in lysosomal storage disorders, whereas peripheral forms are a key feature of mitochondrial disease. Furthermore, oculogyric crisis is an important feature in disorders affecting dopamine syntheses or transport. Ocular motor disorders are often not reported by the patient, and abnormalities can be easily overlooked in a general examination. In adults with unexplained psychiatric and neurological symptoms, a special focus on examination of eye movements can serve as a relatively simple clinical tool to detect a metabolic disorder. Eye movements can be easily quantified and analyzed with video‐oculography, making them a valuable biomarker for following the natural course of disease or the response to therapies. Here, we review, for the first time, eye movement disorders that can occur in inborn errors of metabolism, with a focus on late‐onset forms. We provide a step‐by‐step overview that will help clinicians to examine and interpret eye movement disorders. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Clinical Metabolomics to Segregate Aromatic Amino Acid Decarboxylase Deficiency From Drug-Induced Metabolite Elevations

BACKGROUND

Phenotyping technologies featured in the diagnosis of inborn errors of metabolism, such as organic acid, amino acid, and acylcarnitine analyses, recently have been supplemented by broad-scale untargeted metabolomic phenotyping. We investigated the analyte changes associated with aromatic amino acid decarboxylase (AADC) deficiency and dopamine medication treatment.

METHODS

Using an untargeted metabolomics platform, we analyzed ethylenediaminetetraacetic acid plasma specimens, and biomarkers were identified by comparing the biochemical profile of individual patient samples to a pediatric-centric population cohort.

RESULTS

Elevated 3-methoxytyrosine (average z score 5.88) accompanied by significant decreases of dopamine 3-O-sulfate (-2.77), vanillylmandelate (-2.87), and 3-methoxytyramine sulfate (-1.44) were associated with AADC deficiency in three samples from two patients. In five non-AADC patients treated with carbidopa-levodopa, levels of 3-methoxytyrosine were elevated (7.65); however, the samples from non-AADC patients treated with DOPA-elevating drugs had normal or elevated levels of metabolites downstream of aromatic l-amino acid decarboxylase, including dopamine 3-O-sulfate (2.92), vanillylmandelate (0.33), and 3-methoxytyramine sulfate (5.07). In one example, a plasma metabolomic phenotype pointed to a probable AADC deficiency and prompted the evaluation of whole exome sequencing data, identifying homozygosity for a known pathogenic variant, whereas whole exome analysis in a second patient revealed compound heterozygosity for two variants of unknown significance.

CONCLUSIONS

These data demonstrate the power of combining broad-scale genotyping and phenotyping technologies to diagnose inherited neurometabolic disorders and suggest that metabolic phenotyping of plasma can be used to identify AADC deficiency and to distinguish it from non-AADC patients with elevated 3-methoxytyrosine caused by DOPA-raising medications.

Natural History of Aromatic L-Amino Acid Decarboxylase Deficiency in Taiwan

OBJECTIVES

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare inherited disorder of monoamine neurotransmitter synthesis; this deficiency leads to psychomotor delay, hypotonia, oculogyric crises, dystonia, and extraneurological symptoms. This study aimed to provide further insight into the clinical course of AADC deficiency in Taiwan.

PATIENTS AND METHODS

We present a retrospective, descriptive, single-center study of 37 children with a confirmed diagnosis of AADC deficiency. Their medical histories were reviewed for motor milestones, motor development, DDC mutation, and body weight. The termination point for each patient in this study was defined as no further follow-up, death, or enrollment in a gene therapy trial.

RESULTS

The median age of the study patients at the end of the study was 4.39 years (1.28-11.30). Of the 37 patients, 36 did not develop full head control, sitting ability, standing ability, or speech at any time point from birth to the termination points. Motor scales were administered to 22 patients. Their Alberta Infant Motor Scale scores were below the fifth percentile, and their Peabody Developmental Motor Scales, Second Edition, scores were below the first percentile. Their body weights were normal in the first few months of life, but severe growth retardation occurred at later ages. The mutation c.714+4A>T (IVS6+4A>T) accounted for 76% of all their DDC mutations.

CONCLUSION

In this chapter, we report the clinical course of AADC deficiency in Taiwan. Our data will help guide the development of treatment strategies for the disease.