A novel mechanism of idiopathic orthostatic hypotension and hypocatecholaminemia due to autoimmunity against aromatic l-Amino acid decarboxylase

Orthostatic hypotension (OH) is a common condition. Many potential etiologies of OH have been identified, but in clinical practice the underlying cause of OH is often unknown. In the present study, we identified a novel and extraordinary etiology of OH. We describe a first case of acquired severe OH with syncope, and the female patient had extremely low levels of catecholamines and serotonin in plasma, urine and cerebrospinal fluid (CSF). Her clinical and biochemical evidence showed a deficiency of the enzyme aromatic l-amino acid decarboxylase (AADC), which converts l-DOPA to dopamine, and 5-hydroxytryptophan to serotonin, respectively. The consequence of pharmacologic stimulation of catecholaminergic nerves and radionuclide examination revealed her catecholaminergic nerves denervation. Moreover, we found that the patient's serum showed presence of autoantibodies against AADC, and that isolated peripheral blood mononuclear cells (PBMCs) from the patient showed cytokine-induced toxicity against AADC. These observations suggest that her autoimmunity against AADC is highly likely to cause toxicity to adrenal medulla and catecholaminergic nerves which contain AADC, resulting in hypocatecholaminemia and severe OH. Administration of vitamin B6, an essential cofactor of AADC, enhanced her residual AADC activity and drastically improved her symptoms. Our data thus provide a new insight into pathogenesis and pathophysiology of OH.

Gene therapy for aromatic L-amino acid decarboxylase deficiency: Requirements for safe application and knowledge-generating follow-up

The autosomal recessive defect of aromatic L-amino acid decarboxylase (AADC) leads to a severe neurological disorder with manifestation in infancy due to a pronounced, combined deficiency of dopamine, serotonin and catecholamines. The success of conventional drug treatment is very limited, especially in patients with a severe phenotype. The development of an intracerebral AAV2-based gene delivery targeting the putamen or substantia nigra started more than 10 years ago. Recently, the putaminally-delivered construct, Eladocagene exuparvovec has been approved by the European Medicines Agency and by the British Medicines and Healthcare products Regulatory Agency. This now available gene therapy provides for the first time also for AADC deficiency (AADCD) a causal therapy, leading this disorder into a new therapeutic era. By using a standardized Delphi approach members of the International Working Group on Neurotransmitter related Disorders (iNTD) developed structural requirements and recommendations for the preparation, management and follow-up of AADC deficiency patients who undergo gene therapy. This statement underlines the necessity of a framework for a quality-assured application of AADCD gene therapy including Eladocagene exuparvovec. Treatment requires prehospital, inpatient and posthospital care by a multidisciplinary team in a specialized and qualified therapy center. Due to lack of data on long-term outcomes and the comparative efficacy of alternative stereotactic procedures and brain target sites, a structured follow-up plan and systematic documentation of outcomes in a suitable, industry-independent registry study are necessary.

Neurodegenerative Etiology of Aromatic L-Amino Acid Decarboxylase Deficiency: a Novel Concept for Expanding Treatment Strategies

Aromatic l-amino acid decarboxylase deficiency (AADC-DY) is caused by one or more mutations in the DDC gene, resulting in the deficit in catecholamines and serotonin neurotransmitters. The disease has limited therapeutic options with relatively poor clinical outcomes. Accumulated evidence suggests the involvement of neurodegenerative mechanisms in the etiology of AADC-DY. In the absence of neurotransmitters' neuroprotective effects, the accumulation and the chronic presence of several neurotoxic metabolites including 4-dihydroxy-L-phenylalanine, 3-methyldopa, and homocysteine, in the brain of subjects with AADC-DY, promote oxidative stress and reduce the cellular antioxidant and methylation capacities, leading to glial activation and mitochondrial dysfunction, culminating to neuronal injury and death. These pathophysiological processes have the potential to hinder the clinical efficacy of treatments aimed at increasing neurotransmitters' synthesis and or function. This review describes in detail the mechanisms involved in AADC-DY neurodegenerative etiology, highlighting the close similarities with those involved in other neurodegenerative diseases. We then offer novel strategies for the treatment of the disease with the objective to either reduce the level of the metabolites or counteract their prooxidant and neurotoxic effects. These treatment modalities used singly or in combination, early in the course of the disease, will minimize neuronal injury, preserving the functional integrity of neurons, hence improving the clinical outcomes of both conventional and unconventional interventions in AADC-DY. These modalities may not be limited to AADC-DY but also to other metabolic disorders where a specific mutation leads to the accumulation of prooxidant and neurotoxic metabolites.

Newborn screening for aromatic l-amino acid decarboxylase deficiency - Strategies, results, and implication for prevalence calculations

BACKGROUND

Aromatic l-amino acid decarboxylase deficiency (AADCD) is a rare, autosomal-recessive neurometabolic disorder caused by variants in dopa decarboxylase (DDC) gene, resulting in a severe combined deficiency of serotonin, dopamine, norepinephrine, and epinephrine. Birth prevalence of AADCD varies by population. In pilot studies, 3-O-methyldopa (3-OMD) was shown to be a reliable biomarker for AADCD in high-throughput newborn screening (NBS) allowing an early diagnosis and access to gene therapy. To evaluate the usefulness of this method for routine NBS, 3-OMD screening results from the largest three German NBS centers were analyzed.

METHODS

A prospective, multicenter (n = 3) NBS pilot study evaluated screening for AADCD by quantifying 3-OMD in dried blood spots (DBS) using tandem mass spectrometry (MS/MS).

RESULTS

In total, 766,660 neonates were screened from January 2021 until June 2023 with 766,647 with unremarkable AADCD NBS (766,443 by 1st-tier analysis and 204 by 2nd-tier analysis) and 13 with positive NBS result recalled for confirmatory diagnostics (recall-rate about 1:59,000). Molecular genetic analysis confirmed AADCD (c.79C > T p.[Arg27Cys] in Exon 2 und c.215 A > C p.[His72Pro] in Exon 3) in one infant. Another individual was highly suspected with AADCD but died before confirmation (overall positive predictive value 0.15). False-positive results were caused by maternal L-Dopa use (n = 2) and prematurity (30th and 36th week of gestation, n = 2). However, in 63% (n = 7) the underlying etiology for false positive results remained unexplained. Estimated birth prevalence (95% confidence interval) was 1:766,660 (95% CI 1:775,194; 1:769,231) to 1:383,330 (95% CI 1:384,615; 1:383,142). The identified child remained asymptomatic until last follow up at the age of 9 months.

CONCLUSIONS

The proposed screening strategy with 3-OMD detection in DBS is feasible and effective to identify individuals with AADCD. The estimated birth prevalence supports earlier estimations and confirms AADCD as a very rare disorder. Pre-symptomatic identification by NBS allows a disease severity adapted drug support to diminish clinical complications until individuals are old enough for the application of the gene therapy.

Automatically pre-screening patients for the rare disease aromatic l-amino acid decarboxylase deficiency using knowledge engineering, natural language processing, and machine learning on a large EHR population

OBJECTIVES

Electronic health record (EHR) data may facilitate the identification of rare diseases in patients, such as aromatic l-amino acid decarboxylase deficiency (AADCd), an autosomal recessive disease caused by pathogenic variants in the dopa decarboxylase gene. Deficiency of the AADC enzyme results in combined severe reductions in monoamine neurotransmitters: dopamine, serotonin, epinephrine, and norepinephrine. This leads to widespread neurological complications affecting motor, behavioral, and autonomic function. The goal of this study was to use EHR data to identify previously undiagnosed patients who may have AADCd without available training cases for the disease.

MATERIALS AND METHODS

A multiple symptom and related disease annotated dataset was created and used to train individual concept classifiers on annotated sentence data. A multistep algorithm was then used to combine concept predictions into a single patient rank value.

RESULTS

Using an 8000-patient dataset that the algorithms had not seen before ranking, the top and bottom 200 ranked patients were manually reviewed for clinical indications of performing an AADCd diagnostic screening test. The top-ranked patients were 22.5% positively assessed for diagnostic screening, with 0% for the bottom-ranked patients. This result is statistically significant at P < .0001.

CONCLUSION

This work validates the approach that large-scale rare-disease screening can be accomplished by combining predictions for relevant individual symptoms and related conditions which are much more common and for which training data is easier to create.

Burden of illness of aromatic L-amino acid decarboxylase deficiency: a survey of physicians in Southern Europe

BACKGROUND

Aromatic L-amino acid decarboxylase deficiency (AADCd) is an ultra-rare genetic neurometabolic disorder caused by mutations in the DDC gene.

OBJECTIVE

This retrospective, noninterventional study was designed to describe the burden of AADCd including the associated healthcare resource utilization in Southern Europe.

METHODS

Eleven clinicians completed a patient case study survey for patients with AADCd currently or previously under their care, followed by an interview with each clinician to assess healthcare resource utilization, patient characteristics, and symptoms.

RESULTS

Clinicians provided data for 20 patients with AADCd, of whom 60% were male. All patients experienced movement disorders, 90% exhibited developmental delay, 85% reported sleeping problems, and 80% experienced gastrointestinal problems. The symptoms varied with disease severity. Patients with AADCd received care from more than 16 different specialists including both medical and paramedical healthcare professionals. Hospitalizations and visits to accident and emergency departments were also frequent.

CONCLUSION

In terms of symptoms and healthcare resource utilization, the burden of illness of AADCd is substantial. This study provides insights into several aspects of the disease that are difficult to ascertain from published case reports.

The novel P330L pathogenic variant of aromatic amino acid decarboxylase maps on the catalytic flexible loop underlying its crucial role

Aromatic amino acid decarboxylase (AADC) deficiency is a rare monogenic disease, often fatal in the first decade, causing severe intellectual disability, movement disorders and autonomic dysfunction. It is due to mutations in the gene coding for the AADC enzyme responsible for the synthesis of dopamine and serotonin. Using whole exome sequencing, we have identified a novel homozygous c.989C > T (p.Pro330Leu) variant of AADC causing AADC deficiency. Pro330 is part of an essential structural and functional element: the flexible catalytic loop suggested to cover the active site as a lid and properly position the catalytic residues. Our investigations provide evidence that Pro330 concurs in the achievement of an optimal catalytic competence. Through a combination of bioinformatic approaches, dynamic light scattering measurements, limited proteolysis experiments, spectroscopic and in solution analyses, we demonstrate that the substitution of Pro330 with Leu, although not determining gross conformational changes, results in an enzymatic species that is highly affected in catalysis with a decarboxylase catalytic efficiency decreased by 674- and 194-fold for the two aromatic substrates. This defect does not lead to active site structural disassembling, nor to the inability to bind the pyridoxal 5’-phosphate (PLP) cofactor. The molecular basis for the pathogenic effect of this variant is rather due to a mispositioning of the catalytically competent external aldimine intermediate, as corroborated by spectroscopic analyses and pH dependence of the kinetic parameters. Altogether, we determined the structural basis for the severity of the manifestation of AADC deficiency in this patient and discussed the rationale for a precision therapy.

The impact of caring for an individual with aromatic l-amino acid decarboxylase (AADC) deficiency: a qualitative study and the development of a conceptual model

BACKGROUND

Aromatic l-amino acid decarboxylase (AADC) deficiency is a rare neurological condition, associated with a wide range of symptoms and functional issues, such as profound motor impairment and learning disability. Most individuals with AADC deficiency are completely dependent on their caregivers. This study explored the impact of caring for an individual with AADC deficiency.

METHODS

Qualitative interviews were conducted with caregivers of individuals with AADC deficiency in Italy, Portugal, Spain and the United States. An interview guide was developed with input from clinical experts and caregivers and included questions on the impact of caring for an individual with AADC deficiency. Interviews were conducted by telephone/videoconference and were recorded and transcribed. Data were analysed using thematic analysis.

RESULTS

Fourteen caregivers took part who provided care to 13 individuals with AADC deficiency aged 1-15 years. Caregivers reported that their lives centred around the individual with AADC deficiency, due to their need for 24-hour care and regular healthcare appointments. They reported both proximal impacts (impact on time, planning, physical health and emotional wellbeing), and distal impacts (impact on social/leisure activities, relationships, work and finances). These concepts and relationships were illustrated in a conceptual model.

CONCLUSIONS

This is the first qualitative study to report on the experience of caring for an individual with AADC deficiency. Caregivers reported that caring had a substantial multifaceted impact on their lives. These findings highlight the importance of considering the caregiver experience when evaluating the burden of AADC deficiency.

Aromatic l-amino acid decarboxylase deficiency: a patient-derived neuronal model for precision therapies

Aromatic l-amino acid decarboxylase (AADC) deficiency is a complex inherited neurological disorder of monoamine synthesis which results in dopamine and serotonin deficiency. The majority of affected individuals have variable, though often severe cognitive and motor delay, with a complex movement disorder and high risk of premature mortality. For most, standard pharmacological treatment provides only limited clinical benefit. Promising gene therapy approaches are emerging, though may not be either suitable or easily accessible for all patients. To characterize the underlying disease pathophysiology and guide precision therapies, we generated a patient-derived midbrain dopaminergic neuronal model of AADC deficiency from induced pluripotent stem cells. The neuronal model recapitulates key disease features, including absent AADC enzyme activity and dysregulated dopamine metabolism. We observed developmental defects affecting synaptic maturation and neuronal electrical properties, which were improved by lentiviral gene therapy. Bioinformatic and biochemical analyses on recombinant AADC predicted that the activity of one variant could be improved by l-3,4-dihydroxyphenylalanine (l-DOPA) administration; this hypothesis was corroborated in the patient-derived neuronal model, where l-DOPA treatment leads to amelioration of dopamine metabolites. Our study has shown that patient-derived disease modelling provides further insight into the neurodevelopmental sequelae of AADC deficiency, as well as a robust platform to investigate and develop personalized therapeutic approaches.

Compound heterozygosis in AADC deficiency: A complex phenotype dissected through comparison among heterodimeric and homodimeric AADC proteins

Compound heterozygosis is the most diffuse and hardly to tackle condition in aromatic amino acid decarboxylase (AADC) deficiency, a genetic disease leading to severe neurological impairment. Here, by using an appropriate vector, we succeeded in obtaining high yields of AADC protein and characterizing two new heterodimers, T69M/S147R and C281W/M362T, detected in two AADC deficiency patients. We performed an extensive biochemical characterization of the heterodimeric recombinant proteins and of the related homodimers, by a combination of dichroic and fluorescence spectroscopy and activity assays together with bioinformatic analyses. We found that T69M/S147R exhibits negative complementation in terms of activity but it is more stable than the average of the homodimeric counterparts. The heterodimer C281W/M362T retains a nearly good catalytic efficiency, whereas M362T homodimer is less affected and C281W homodimer is recovered as insoluble. These results, which are consistent with the related phenotypes, and the data emerging from previous studies, suggest that the severity of AADC deficiency is not directly explained by positive or negative complementation phenomena, but rather depends on: i) the integrity of one or both active sites; ii) the structural and functional properties of the entire pool of AADC proteins expressed. Overall, this integrated and cross-sectional approach enables proper characterization and depicts the functional result of subunit interactions in the dimeric structure and will help to elucidate the physio-pathological mechanisms in AADC deficiency.

Detection of 3-O-methyldopa in dried blood spots for neonatal diagnosis of aromatic L-amino-acid decarboxylase deficiency: The northeastern Italian experience

OBJECTIVE

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare inherited autosomal recessive disorder of biogenic amine metabolism. Diagnosis requires analysis of neurotransmitter metabolites in cerebrospinal fluid, AADC enzyme activity analysis, or molecular analysis of the DDC gene. 3-O-methyldopa (3-OMD) is a key screening biomarker for AADC deficiency.

METHODS

We describe a rapid method for 3-OMD determination in dried blood spots (DBS) using flow-injection analysis tandem mass spectrometry with NeoBase™ 2 reagents and ¹³C₆-tyrosine as an internal standard, which are routinely used in high-throughput newborn screening. We assessed variability using quality control samples over a range of 3-OMD concentrations.

RESULTS

Within-day and between-day precision determined with quality control samples demonstrated coefficients of variation <15%. 3-OMD concentrations in 1000 healthy newborns revealed a mean of 1.33 μmol/L (SD ± 0.56, range 0.61-3.05 μmol/L), 100 non-AADC control subjects (age 7 days - 1 year) showed a mean of 1.19 μmol/L (SD ± 0.35-2.00 μmol/L), and 81 patients receiving oral L-Dopa had a mean 3-OMD concentration of 14.90 μmol/L (SD ± 14.18, range 0.4-80.3 μmol/L). A patient with confirmed AADC was retrospectively analyzed and correctly identified (3-OMD 10.51 μmol/L). In April 2020, we started a pilot project for identifying AADC deficiency in DBSs routinely submitted to the expanded newborn screening program. 3-OMD concentrations were measured in 21,867 samples; no patients with AADC deficiency were identified. One newborn had a high 3-OMD concentration due to maternal L-Dopa treatment.

DISCUSSION

We demonstrated a rapid new method to identify AADC deficiency using reagents and equipment already widely used in newborn screening programs. Although our study is limited, introduction of our method in expanded neonatal screening is feasible and could facilitate deployment of screening, allowing for early diagnosis that is important for effective treatment.

AADC deficiency from infancy to adulthood: Symptoms and developmental outcome in an international cohort of 63 patients

Aromatic l-amino acid decarboxylase deficiency (AADCD) is a rare, autosomal recessive neurodevelopmental disorder characterized by impaired synthesis of dopamine, noradrenaline, adrenaline and serotonin, leading to a complex syndrome of motor, behavioral, and autonomic symptoms. This retrospective study assessed the symptoms and developmental outcome of a large international cohort of patients with AADCD via physician and/or caregiver responses to a detailed, standardized questionnaire. Sixty-three patients (60% female; ages 6 months-36 years, median 7 years; 58 living) from 23 individual countries participated. Common symptoms at onset (median age 3 months, range 0-12 months) were hypotonia, developmental delay, and/or oculogyric crises. Oculogyric crises were present in 97% of patients aged 2 to 12 years, occurred in the majority of patients in all age groups, and tended to be most severe during early childhood. Prominent non-motor symptoms were sleep disturbance, irritable mood, and feeding difficulties. The majority of subjects (70%) had profound motor impairment characterized by absent head control and minimal voluntary movement, while 17% had mild motor impairment and were able to walk independently. Dopamine agonists were the medications most likely to produce some symptomatic benefit, but were associated with dose-limiting side effects (dyskinesia, insomnia, irritability, vomiting) that led to discontinuation 25% of the time. The age distribution of our cohort (70% of subjects under age 13 years) and the observation of a greater proportion of patients with a more severe disease phenotype in the younger compared to the older patients, both suggest a significant mortality risk during childhood for patients with severe disease.

Semi-quantitative detection of a vanillactic acid/vanillylmandelic acid ratio in urine is a reliable diagnostic marker for aromatic L-amino acid decarboxylase deficiency

BACKGROUND

Aromatic L-amino acid decarboxylase (AADC) deficiency is a primary neurotransmitter defect of the biosynthesis of catecholamines and serotonin. The phenotype consists of varying degrees of neurological impairment, including motor and non-motor symptoms. Treatment outcomes correlate with the time point of diagnosis and treatment initiation; therefore, reliable diagnostic markers are necessary. Increased vanillactic acid (VLA) concentrations in the analysis of organic acids in urine have been reported in AADC deficiency. However, this elevation is often subtle and easily missed. In this study, we evaluate the semi-quantitative determination of VLA and vanillylmandelic acid (VMA) concentrations and establish the ratio of a VLA/VMA as a novel diagnostic marker for AADC deficiency.

METHODS

Urine samples obtained from 10,095 non-AADC deficient controls and 14 confirmed AADC deficient patients were used for organic acid analysis by liquid-liquid extraction of the acidified samples and gas chromatographic-mass spectrometric separation after trimethylsilylation. The semi-quantitative determination of VLA and VMA concentrations and the calculation of a VLA/VMA ratio were evaluated as a diagnostic marker for AADC deficiency.

RESULTS

The mean VLA and VMA concentrations in 10,095 non-AADCD samples was 0.3 mmol/mol creatinine (SD = 1.18, range 0-57.79) and 5.59 mmol/mol creatinine (SD = 3.87, range 0.04-60.62), respectively. The mean concentration of VLA in 14 patient-derived samples was 10.24 mmol/mol creatinine, (SD = 11.58, range = 0.37-33.06) and 0.45 mmol/mol creatinine for VMA (SD = 0.29, range 0.11-1.27). The mean VLA/VMA ratio in non-AADC controls was 0.07 (SD = 0.37, range 0.0-23.24), whereas AADC deficient patients revealed a mean VLA/VMA ratio of 23.16 (SD = 22.83, range 0.97-74.1). The VLA/VMA ratio thus allows a reliable identification of patients with AADC deficiency, especially in the young age cohort as it decreases with age. To take this into account, age-adjusted thresholds have been developed.

CONCLUSION

Determination of individual concentrations of VLA and VMA in urine does not allow a reliable diagnosis of AADC deficiency. In this study, we could demonstrate that a semi-quantitative analysis of organic acids in urine allows the formation of metabolite ratios and that the VLA/VMA ratio is a reliable, easily accessible, new parameter for the diagnosis of AADC deficiency.

High throughput newborn screening for aromatic ʟ-amino-acid decarboxylase deficiency by analysis of concentrations of 3-O-methyldopa from dried blood spots

Aromatic l-amino-acid decarboxylase (AADC) deficiency is an inherited disorder of biogenic amine metabolism with a broad neurological phenotype. The clinical symptoms overlap with other diseases resulting in an often delayed diagnosis. Innovative disease-changing treatment options, particularly gene therapy, have emphasised the need for an early diagnosis. We describe the first method for 3-O-methyldopa (3-OMD) analysis in dried blood spots (DBS) suitable for high throughput newborn screening (NBS). We established a novel tandem mass spectrometry method to quantify 3-OMD in DBS and successfully tested it in 38 888 unaffected newborns, 14 heterozygous DDC variant carriers, seven known AADC deficient patients, and 1079 healthy control subjects. 3-OMD concentrations in 38 888 healthy newborns revealed a mean of 1.16 μmol/L (SD = 0.31, range 0.31-4.6 μmol/L). 1079 non-AADC control subjects (0-18 years) showed a mean 3-OMD concentration of 0.78 μmol/L (SD = 1.75, range 0.24-2.36 μmol/L) with a negative correlation with age. Inter- and intra-assay variability was low, and 3-OMD was stable over 32 days under different storage conditions. We identified seven confirmed AADC deficient patients (mean 3-OMD 9.88 μmol/L [SD = 13.42, range 1.82-36.93 μmol/L]). The highest concentration of 3-OMD was found in a NBS filter card of a confirmed AADC deficient patient with a mean 3-OMD of 35.95 μmol/L. 14 DDC variant carriers showed normal 3-OMD concentrations. We demonstrate a novel high-throughput method to measure 3-OMD in DBS, which allows integration in existing NBS programs enabling early diagnosis of AADC deficiency.

Prevalence of Aromatic l-Amino Acid Decarboxylase Deficiency in At-Risk Populations

BACKGROUND

Aromatic l-amino acid decarboxylase (AADC) deficiency is an autosomal recessive metabolic disorder that results from disease-causing pathogenic variants of the dopa decarboxylase (DDC) gene. Loss of dopamine and serotonin production in the brain from infancy prevents achievement of motor developmental milestones.

METHODS

We retrospectively evaluated data obtained from requests to Medical Neurogenetics Laboratories for analyses of neurotransmitter metabolites in the cerebrospinal fluid, AADC enzyme activity in plasma, and/or Sanger sequencing of the DDC gene. Our primary objective was to estimate the prevalence of AADC deficiency in an at-risk population.

RESULTS

Approximately 20,000 cerebrospinal fluid samples were received with a request for neurotransmitter metabolite analysis in the eight-year study period; 22 samples tested positive for AADC deficiency based on decreased concentrations of 5-hydroxyindoleacetic acid and homovanillic acid, and increased 3-O-methyldopa, establishing an estimated prevalence of approximately 0.112%, or 1:900. Of the 81 requests received for plasma AADC enzyme analysis, 25 samples had very low plasma AADC activity consistent with AADC deficiency, resulting in identification of nine additional cases. A total of five additional patients were identified by Sanger sequencing as the primary request leading to the diagnosis of AADC deficiency.

CONCLUSIONS

Overall, these analyses identified 36 new cases of AADC deficiency. Sequencing findings showed substantial diversity with identification of 26 different DDC gene variants; five had not previously been associated with AADC deficiency. The results of the present study align with the emerging literature and understanding of the epidemiology and genetics of AADC deficiency.

A novel compound heterozygous genotype associated with aromatic amino acid decarboxylase deficiency: Clinical aspects and biochemical studies

Aromatic amino acid decarboxylase (AADC) deficiency is a rare autosomal neurometabolic disorder caused by a deficit of AADC, a pyridoxal 5'-phosphate (PLP)-dependent enzyme, which catalyzes the synthesis of dopamine and serotonin. While many studies have highlighted the molecular defects of the homozygous pathogenic variants, so far only a study investigated heterozygous variants at protein level. Here, we report a clinical case of one AADC deficiency compound heterozygous patient bearing the A91V mutation and the novel C410G mutation. To elucidate its enzymatic phenotype, the A91V and C410G homodimers were first expressed in Escherichia coli, purified and characterized. Although both apo variants display an unaltered overall tertiary structure, they show a ̴ 20-fold decreased PLP binding affinity. The C410G mutation only causes a ̴ 4-fold decrease of the catalytic efficiency, while the A91V mutation causes a 1300-fold decrease of the k_cat/K_m, and changes in the holoAADC consisting in a marked alteration of the tertiary structure and the coenzyme microenvironment. Structural analyses of these mutations are in agreement with these data. Unfortunately, the C410G/A91V heterodimer was constructed, expressed and purified in rather modest amount. Anyway, measurements of decarboxylase activity indicate that its putative k_cat value is lower than that predicted by averaging the k_cat values of the two parental enzymes. This indicates a negative interallelic complementation between the C410G and A91V monomers. Overall, this study allowed to relate the clinical to the enzymatic phenotype of the patient and to extend knowledge in the clinical and molecular pathogenesis of AADC deficiency.

Aromatic amino acid decarboxylase deficiency: Molecular and metabolic basis and therapeutic outlook

Aromatic-l-amino acid decarboxylase (AADC) deficiency is an ultra-rare inherited autosomal recessive disorder characterized by sharply reduced synthesis of dopamine as well as other neurotransmitters. Symptoms, including hypotonia and movement disorders (especially oculogyric crisis and dystonia) as well as autonomic dysfunction and behavioral disorders, vary extensively and typically emerge in the first months of life. However, diagnosis is difficult, requiring analysis of metabolites in cerebrospinal fluid, assessment of plasma AADC activity, and/or DNA sequence analysis, and is frequently delayed for years. New metabolomics techniques promise early diagnosis of AADC deficiency by detection of 3-O-methyl-dopa in serum or dried blood spots. A total of 82 dopa decarboxylase (DDC) variants in the DDC gene leading to AADC deficiency have been identified and catalogued for all known patients (n = 123). Biochemical and bioinformatics studies provided insight into the impact of many variants. c.714+4A>T, p.S250F, p.R347Q, and p.G102S are the most frequent variants (cumulative allele frequency = 57%), and c.[714+4A>T];[714+4A>T], p.[S250F];[S250F], and p.[G102S];[G102S] are the most frequent genotypes (cumulative genotype frequency = 40%). Known or predicted molecular effect was defined for 79 variants. Most patients experience an unrelenting disease course with poor or no response to conventional medical treatments, including dopamine agonists, monoamine oxidase inhibitors, and pyridoxine derivatives. The advent of gene therapy represents a potentially promising new avenue for treatment of patients with AADC deficiency. Clinical studies based on the direct infusion of engineered adeno-associated virus type 2 vectors into the putamen have demonstrated acceptable safety and tolerability and encouraging improvement in motor milestones and cognitive symptoms. The success of gene therapy in AADC deficiency treatment will depend on timely diagnosis to facilitate treatment administration before the onset of neurologic damage.

Melatonin-deficient rice plants show a common semidwarf phenotype either dependent or independent of brassinosteroid biosynthesis

Melatonin-deficient rice with a semidwarf erect-leaf phenotype was created by suppressing serotonin N-acetyltransferase 2 (SNAT2). We generated an RNAi transgenic rice that suppressed tryptophan decarboxylase (TDC), which encodes the first TDC enzyme committed step for melatonin biosynthesis in plants catalyzing the conversion of tryptophan into tryptamine, to determine whether other transgenic rice with downregulated melatonin biosynthetic genes exhibited the same erect-leaf phenotype as the snat2 RNAi rice. The TDC RNAi rice produced significantly less melatonin than the wild type and exhibited a semidwarf phenotype, but no erect-leaf phenotype was observed. In contrast, tryptamine 5-hydroxylase (T5H) knockout Sekiguchi rice and caffeic acid O-methyltransferase (COMT) RNAi rice seedlings were semidwarf phenotypes with erect leaves, as was the snat2 RNAi rice due to a melatonin deficiency. All RNAi rice plants showing erect-leaf phenotypes had lower expression levels of the DWARF4 gene, which is a key enzyme for brassinosteroid (BR) biosynthesis, leading to lower BR levels than their respective wild types. Suppressing melatonin synthesis did not alter the contents of indole 3-acetic acid (IAA), suggesting the irrelevance of melatonin deficiency to IAA biosynthesis. These data indicate that a semidwarf seedling is a common rice phenotype by the lack of melatonin synthesis with or without BR suppression in a melatonin biosynthetic gene-specific manner.

A novel DDC gene deletion mutation in two Chinese mainland siblings with aromatic l-amino acid decarboxylase deficiency

BACKGROUND

Aromatic l-amino acid decarboxylase (AADC) deficiency (OMIM #608643) is a rare and severe disorder of biogenic amine synthesis caused by mutations in the DDC gene. The phenomenology of the movement disorder includes intermittent oculogyric crises and limb dystonia, generalized athetosis, and impaired voluntary movement.

OBJECTIVE

To identify clinical manifestations and DDC gene mutations in two Chinese mainland children who are siblings with AADC deficiency.

METHODS

We used targeted next-generation sequencing and quantitative polymerase chain reaction (qPCR) to reveal DDC mutations in these children.

RESULTS

Two DDC gene mutations were found: one missense mutation, c.1040G > A (p.Arg347Gln), is a reported mutation derived from the mother; the other mutation, a whole-exon 11 and 12 deletion, is a novel mutation derived from the father. The index patient and her brother both had poor sucking power and feeding difficulty at birth and episodes of oculogyric crises, truncal hypotonia, limb hypertonia, sleep disturbances, irritability, and motor delay. The siblings both died at 1 year and 10 months due to asphyxia and pneumonia during gaze and hypertonia episodes.

CONCLUSION

This study identified a novel DDC gene deletion mutation in two siblings with AADC deficiency disease in the Chinese mainland population.

When dysphoria is not a primary mental state: A case report of the role of the aromatic L-aminoacid decarboxylase

RATIONALE

The aromatic L-amino acid decarboxylase (AADC) deficiency (AADCD) is a rare, autosomal recessive neurometabolic disorder caused by a deficit of the AADC that is involved in serotonin and dopamine biosynthesis, causing as a consequence, their deficits, but also a lack of norepinephrine and epinephrine, given that dopamine is their precursor.

PATIENT CONCERNS

We report the case of a Caucasian 43-year-old woman heterozygous for p.Ser250Phe in DDC, encoding for AADC with a positive family history for behavioral problems.

DIAGNOSES

Since adolescence, she manifested behavioral abnormalities. Three months before the admission to our hospital, she presented with a permanent dystonic posture at the 4 limbs with numbness and tingling, diplopia, and low potassium levels. She was treated with muscle relaxants and potassium, but with no results. Olanzapine was administrated, worsening mood problems. Later, after fever, low potassium levels, and increased difficulty to move, she was admitted to the neurology unit where, after bradycardia alternating with atrial and ventricular fibrillation, she had loss of consciousness. She started to complain involuntary parossistic eye and head movements, bilateral ptosis, oculogyric crises with dystonia of the head, muscle hypotrophy, and absent deep tendon reflexes. During the hospital stay, she continued having episodes of untreatable bradycardia and fever.

INTERVENTIONS

Hemocultures were performed, resulting positive for Enterococcus faecalis and Acinetobacter baumanii. Whole exome sequencing was performed evidencing that the patient harbored the heterozygous p.Ser250Phe variant in the gene DDC.

OUTCOMES

A treatment with Pyridoxine and Pramipexole was prescribed, but never started because she died.

LESSONS

The heterozygosity for p.Ser250Phe may have influenced the clinical manifestations, given that the patient presented some overlapping symptoms with those in AADCD, but while AADCD normally is diagnosed during childhood, the fact that the patient carried the mutation in heterozygosity may have alleviated and delayed the clinical manifestations.

Consensus guideline for the diagnosis and treatment of aromatic l-amino acid decarboxylase (AADC) deficiency

Aromatic L-amino acid decarboxylase deficiency (AADCD) is a rare, autosomal recessive neurometabolic disorder that leads to a severe combined deficiency of serotonin, dopamine, norepinephrine and epinephrine. Onset is early in life, and key clinical symptoms are hypotonia, movement disorders (oculogyric crisis, dystonia, and hypokinesia), developmental delay, and autonomic symptoms.In this consensus guideline, representatives of the International Working Group on Neurotransmitter Related Disorders (iNTD) and patient representatives evaluated all available evidence for diagnosis and treatment of AADCD and made recommendations using SIGN and GRADE methodology. In the face of limited definitive evidence, we constructed practical recommendations on clinical diagnosis, laboratory diagnosis, imaging and electroencephalograpy, medical treatments and non-medical treatments. Furthermore, we identified topics for further research. We believe this guideline will improve the care for AADCD patients around the world whilst promoting general awareness of this rare disease.

[Feeding difficulty and developmental delay for 8 months and nystagmus for 4 months in an infant]

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive hereditary disease and is a congenital metabolic disorder of neurotransmitter biosynthesis. It is mainly manifested as hypotonia, oculogyric crisis, autonomic dysfunction, and developmental delay. This article reports a boy manifested as delayed motor development, hypotonia, and oculogyric crisis. Gene screening for metabolic disorders revealed new compound heterozygous mutations, c.1063dupA (p.I355fs) and c.250A>C (p.S84R), in the exon of DDC gene. The boy had a significant increase in 3-O-methyldopa as measured by dried blood spot. Therefore, he was diagnosed with AADC deficiency. After treatment with the dopamine receptor agonist pramipexole dihydrochloride, the catechol-O-methyltransferase inhibitor entacapone, and vitamin B6, the boy showed mild improvements in hypotonia, blepharoptosis, and oculogyric crisis. Clinical physicians should enhance their ability for identifying AADC deficiency, so as to facilitate early diagnosis and treatment of this disorder. Genetic counseling for birth health and prenatal diagnosis should be performed for parents in need.

3-O-methyldopa levels in newborns: Result of newborn screening for aromatic l-amino-acid decarboxylase deficiency

BACKGROUND

The diagnosis of aromatic l-amino-acid decarboxylase (AADC) deficiency is often delayed because a cerebrospinal fluid analysis is required to detect a neurotransmitter deficiency. We here demonstrated that an elevated concentration of l-dopa metabolite 3-O-methyldopa (3-OMD) in dried blood spots could be integrated into newborn screening program to precisely predict AADC deficiency.

METHODS

After obtaining parental consent, an additional spot was punched from newborn filter paper, eluted, cleaned, and analyzed by tandem mass spectrometry. Newborns with a 3-OMD concentration exceeding 500ng/mL were referred for confirmatory testing.

RESULTS

From September 2013 to December 2015, 127,987 newborns were screened for AADC deficiency. The mean 3-OMD concentration in these newborns was 88.08ng/mL (SD=27.74ng/mL). Four newborns exhibited an elevated 3-OMD concentration (range, 939-3241ng/mL). All four newborns were confirmed to carry two pathologic DDC mutations, indicating an incidence of AADC deficiency of 1:32,000. During the follow-up period, three patients developed typical symptoms of AADC deficiency. Among 16 newborns with mildly elevated 3-OMD levels, six were heterozygous for the DDC IVS6+4A>T mutation.

CONCLUSION

Newborn screening of AADC deficiency was achieved with a 100% positive-predictive rate. An association for gestational age could be further elucidated.

Aromatic L-amino acid decarboxylase deficiency diagnosed by clinical metabolomic profiling of plasma

Aromatic L-amino acid decarboxylase (AADC) deficiency is an inborn error of metabolism affecting the biosynthesis of serotonin, dopamine, and catecholamines. We report a case of AADC deficiency that was detected using the Global MAPS platform. This is a novel platform that allows for parallel clinical testing of hundreds of metabolites in a single plasma specimen. It uses a state-of-the-art mass spectrometry platform, and the resulting spectra are compared against a library of ~2500 metabolites. Our patient is now a 4 year old boy initially seen at 11 months of age for developmental delay and hypotonia. Multiple tests had not yielded a diagnosis until exome sequencing revealed compound heterozygous variants of uncertain significance (VUS), c.286G>A (p.G96R) and c.260C>T (p.P87L) in the DDC gene, causal for AADC deficiency. CSF neurotransmitter analysis confirmed the diagnosis with elevated 3-methoxytyrosine (3-O-methyldopa). Metabolomic profiling was performed on plasma and revealed marked elevation in 3-methoxytyrosine (Z-score +6.1) consistent with the diagnosis of AADC deficiency. These results demonstrate that the Global MAPS platform is able to diagnose AADC deficiency from plasma. In summary, we report a novel and less invasive approach to diagnose AADC deficiency using plasma metabolomic profiling.

What is new for monoamine neurotransmitter disorders?

The monoamine neurotransmitter disorders are increasingly recognized as an expanding group of inherited neurometabolic syndromes caused by disturbances in the synthesis, transport and metabolism of the biogenic amines, including the catecholamines (dopamine, norepinephrine, and epinephrine) and serotonin. Disturbances in monoamine metabolism lead to neurological syndromes that frequently mimic other conditions, such as hypoxic ischemic encephalopathy, cerebral palsy, parkinsonism-dystonia syndromes, primary genetic dystonia and paroxysmal disorders. As a consequence, neurotransmitter disorders are frequently misdiagnosed. Early and accurate diagnosis of these neurotransmitter disorders is important, as many are highly amenable to, and some even cured by, therapeutic intervention. In this review, we highlight recent advances in the field, particularly the recent extensive characterization of known neurotransmitter disorders and identification of novel neurotransmitter disorders. We also provide an overview of current and future research in the field focused on developing novel treatment strategies.

Aromatic L-amino acid decarboxylase deficiency is a cause of long-fasting hypoglycemia

OBJECTIVE/CONTEXT: Long-fasting hypoglycemia in children may be induced by neurotransmitter disorders.

CASE REPORT

A 5-year-old girl with a medical history of chronic diarrhea presented three episodes of severe hypoglycemia (20 mg/dL) between ages 3 and 5 years. She became pale and sweaty with hypothermia (33.5°C), bradycardia (45 bpm), and acidosis and presented a generalized seizure. During the 17-hour fast test performed to determine the etiology of her hypoglycemia, insulin and C-peptide were appropriately low, and human GH, IGF-I, cortisol, amino acids, and acylcarnitines were in the usual range for fasting duration. However, the presence of vanillactic and vanilpyruvic acids in urine led us to investigate the metabolism of dopamine and serotonin in the cerebrospinal fluid. Indeed, these results indicated an aromatic L-amino acid decarboxylase deficiency that impairs the synthesis of serotonin, dopamine, and catecholamines. The diagnosis was confirmed by the low aromatic L-amino acid decarboxylase (AADC) enzyme activity in plasma (5 pmol/min/mL; reference value, 20-130) and the presence of two heterozygous mutations, c.97G>C (p.V33L, inherited from her father) and c.1385G>C (p.R462P, inherited from her mother) in the DCC gene. She was supplemented with pyridoxine and raw cornstarch (1 g/kg) at evening dinner to reduce the night fast. The episodes of hypoglycemia and the chronic diarrhea were suppressed.

CONCLUSION

Here is the first case report of long-fasting hypoglycemia due to a nontypical AADC deficiency. Hypoglycemia was severe, but the other neurological clinical hallmarks present in AADC-deficient patients were mild to moderate. Thus, neurotransmitter disorders should be considered in any patients presenting hypoglycemia with urine excretion of vanillactic acid.

AADC deficiency: occurring in humans, modeled in rodents

Aromatic l-amino acid decarboxylase (AADC) is a homodimeric pyridoxal phosphate-dependent enzyme responsible for the syntheses of dopamine and serotonin. Defects in the AADC gene result in neurotransmitter deficiencies. Patients with AADC deficiency have severe motor and autonomic dysfunctions. A mouse model of AADC deficiency was recently established. These mice grow poorly and move awkwardly during infancy. They also show high anxiety when they grow up. Because drug therapy provides little or no benefit for many patients with AADC deficiency, a gene therapy has been attempted. The gene therapy employed an adeno-associated virus viral vector that can express the human AADC protein. The vector was injected to the brain of several children with AADC deficiency. The therapy was well tolerated, and all treated patients showed improvement. In the future, the mouse model will also help the development of treatments for AADC deficiency.

Monoamine neurotransmitter deficiencies

Pediatric neurotransmitter disorders refer to a constellation of inherited neurometabolic syndromes attributable to disturbances of neurotransmitter synthesis, degradation, or transport. Monoamine deficiencies represent defects in synthesis of dopamine, serotonin, norepinephrine, and epinephrine or in availability of tetrahydrobiopterin, an important cofactor for monoamine synthesis. Some disorders do not manifest peripheral hyperphenyalaninemia and require CSF neurotransmitter metabolite assay for diagnosis. These include Segawa dopa-responsive dystonia and enzymatic deficiencies of aromatic amino acid decarboxylase, tyrosine hydroxylase, and sepiapterin reductase. The first, autosomal dominantly inherited GTP cyclohydrolase deficiency, has a satisfying response to therapy at any age with benefits maintained over time. The others have more severe and treatment-refractory phenotypes, typically with manifestations well beyond movement disorders. Disorders detectable by elevated serum phenylalanine are deficiencies of GTP cyclohydrolase (homozygous), pterin-carbinolamine dehydratase, dihydropteridine reductase, and pyruvoyl-tetrahydropterin synthase. The latter is the most prevalent and heterogeneous but typically has infantile onset with extrapyramidal as well as bulbar, hypothalamic, limbic, and epileptic manifestations. There are therapeutic roles for neurotransmitter supplementation, and dopaminergic agonists. Basal ganglia calcifications in dihydropteridine reductase deficiency are reversible with folinic acid. Deficiencies of monoamine degradation lead to cognitive, behavioral, and autonomic disorders.

[Pediatric neurotransmitter disease in Japan]

Pediatric neurotransmitter disease (PND) encompasses a range of rare genetic disorders that affect the metabolism of neurotransmitters in children. While these neurological disorders are often studied independently of each other, they all manifest central nervous system symptoms and require proper diagnosis and intervention at early stages. Since clinical symptoms of PND can be nonspecific, the conditions are often under-diagnosed, leaving patients without a chance to receive effective treatment. Envisioning PND as a whole, a comprehensive research effort is underway for a better understanding of pathophysiology and epidemiology in Japan, and toward the establishment of diagnostic criteria. The early diagnosis and development of new effective therapies are of urgent importance for these rare disorders that are not covered by newborn mass screening. For rarer forms of PND, at the same time, it is important to encourage recognition and understanding of the disease concept among healthcare professionals.

Molecular insights into the pathogenicity of variants associated with the aromatic amino acid decarboxylase deficiency

Dopa decarboxylase (DDC or AADC) is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the decarboxylation of L-aromatic amino acids into the corresponding aromatic amines. AADC deficiency is an inborn error of neurotransmitters biosynthesis with an autosomal recessive inheritance. About 30 pathogenic mutations have been identified, but the enzymatic phenotypes causing AADC deficiency are unknown, and the therapeutic management is challenging. Here, we report biochemical and bioinformatic analyses of the human wild-type DDC and the pathogenic variants G102S, F309L, S147R and A275T whose mutations concern amino acid residues at or near the active site. We found that the mutations cause, even if to different extents, a decreased PLP binding affinity (in the range 1.4-170-fold), an altered state of the bound coenzyme and of its microenvironment, and a reduced catalytic efficiency (in the range 17-930-fold). Moreover, as compared to wild-type, the external aldimines formed by the variants with L-aromatic amino acids exhibit different spectroscopic features, do not protect against limited proteolysis, and lead to the formation, in addition to aromatic amines, of cyclic-substrate adducts. This suggests that these external Schiff bases are not properly oriented and anchored, i.e., in a conformation not completely productive for decarboxylation. The external aldimines that the variants form with D-Dopa also appear not to be correctly located at their active site, as suggested by the rate constants of PLP-L-Dopa adduct production higher than that of the wild-type. The possible therapeutic implications of the data are discussed in the light of the molecular defects of the pathogenic variants.

Urinary dopamine in aromatic L-amino acid decarboxylase deficiency: the unsolved paradox

INTRODUCTION

In aromatic L-amino acid decarboxylase (AADC) deficiency, a neurotransmitter biosynthesis defect, paradoxical normal or increased levels of urinary dopamine have been reported. Genotype/phenotype correlations or alternative metabolic pathways may explain this remarkable finding, but were never studied systematically.

METHODS

We studied the mutational spectrum and urinary dopamine levels in 20 patients with AADC-deficiency. Experimental procedures were designed to test for alternative metabolic pathways of dopamine production, which included alternative substrates (tyramine and 3-methoxytyrosine) and alternative enzymes (tyrosinase and CYP2D6).

RESULTS/DISCUSSION

In 85% of the patients the finding of normal or increased urinary levels of dopamine was confirmed, but a relation with AADC genotype could not be identified. Renal microsomes containing CYP2D were able to convert tyramine into dopamine (3.0 nmol/min/g protein) but because of low plasma levels of tyramine this is an unlikely explanation for urinary dopamine excretion in AADC-deficiency. No evidence was found for the production of dopamine from 3-methoxytyrosine. Tyrosinase was not expressed in human kidney.

CONCLUSION

Normal or increased levels of urinary dopamine are found in the majority of AADC-deficient patients. This finding can neither be explained by genotype/phenotype correlations nor by alternative metabolic pathways, although small amounts of dopamine may be formed via tyramine hydroxylation by renal CYP2D6. CYP2D6-mediated conversion of tyramine into dopamine might be an interesting target for the development of new therapeutic strategies in AADC-deficiency.

Aromatic L-amino acid decarboxylase deficiency: clinical features, drug therapy and follow-up

BACKGROUND

Aromatic L-amino acid decarboxylase (AADC) deficiency is a disorder of biogenic amine metabolism resulting in generalized combined deficiency of serotonin, dopamine and catecholamines. Main clinical features are developmental delay, muscular hypotonia, dystonia, oculogyric crises and additional extraneurological symptoms. Response to therapy has been variable and unsatisfactory; the overall prognosis is guarded.

METHODS

To gain more insight into this rare disorder we collected clinical and laboratory data of nine German patients. All patients were clinically examined by one investigator, and their responses to different drug regimes were evaluated by the patients' charts.

RESULTS

Symptoms were obvious from early infancy. Later, main neurological features were truncal muscular hypotonia, hypokinesia, oculogyric crises and rigor. Three patients had single seizures. All patients presented distinct extraneurological symptoms, such as hypersalivation, hyperhidrosis, nasal congestion, sleep disturbances and hypoglycaemia. In CSF all patients revealed the pattern typical of AADC with decreased concentrations of homovanillic and 5-hydroxyindoleacetic acid and elevated concentration of 3-ortho-methyldopa. Diagnosis was confirmed by measurement of AADC activity in plasma in all patients. Drug regimes consisted of vitamin B6, dopamine agonists, MAO inhibitors and anticholinergics in different combinations. No patient achieved a complete recovery from neurological symptoms, but partial improvement of mobility and mood could be achieved in some.

CONCLUSION

AADC deficiency is a severe neurometabolic disorder, characterized by muscular hypotonia, dystonia, oculogyric crises and additional extraneurological symptoms. Medical treatment is challenging, but a systematic trial of the different drugs is worthwhile.

Neuroimaging findings in children with paediatric neurotransmitter diseases

Paediatric neurotransmitter diseases consist of a group of inherited neurometabolic diseases in children, and include disorders related to gamma-amino butyric acid (GABA) metabolism, monoamine biosynthesis, etc. The diagnosis of paediatric neurotransmitter diseases remain a great challenge for paediatricians and child neurologists. In addition to clinical manifestations and CSF neurotransmitter measurement, neuroimaging findings can also be very informative for the diagnosis and evaluation of the patients. For patients with monoamine biosynthesis disorders, the functional evaluation of dopaminergic transmission also plays an important role. Understanding of the possible neuroimaging changes in paediatric neurotransmitter diseases is therefore of great value for the investigation of these patients.

A new perspective on the treatment of aromatic L-amino acid decarboxylase deficiency

The final step in production of the neurotransmitters dopamine and serotonin is catalyzed by aromatic l-amino acid decarboxylase (AADC). AADC deficiency is a debilitating genetic condition that results in a deficit in these neurotransmitters, and manifests in infancy as a severe movement disorder with developmental delay. Response to current treatments is often disappointing. We have reviewed the literature to look for improvements to the current treatment strategy and also for new directions for AADC deficiency treatment. There may be differences in the mode of action, side-effect risk and effectiveness between different dopamine agonists and monoamine oxidase inhibitors currently used for AADC deficiency treatment. The range of these drugs used requires re-evaluation as some may have greater efficacy than others. Pyridoxal 5'-phosphate, the AADC cofactor may stabilize AADC and could increase AADC activity. Pyridoxal 5'-phosphate could have advantages as a treatment instead of pyridoxine. Atypical neuroleptics and peripheral AADC inhibitors both increase AADC activity in vivo and could be a future direction for AADC deficiency treatment and related conditions. Parkinson's disease gene therapy to deliver and express the human AADC gene in striatum is being tested in humans. Consequently gene therapy for AADC deficiency could be a realistic aim however an animal model of AADC deficiency is important for further progression.

Unusually mild phenotype of AADC deficiency in 2 siblings

Aromatic L-amino acid decarboxylase deficiency is a rare neurotransmitter defect leading to serotonin, dopamine and norepinephrine deficiency. Affected individuals usually present in infancy with severe developmental delay, oculogyric crises and extrapyramidal movements. We present the clinical, molecular and biochemical features of a pair of siblings who presented with fatigability, hypersomnolence and dystonia and who showed excellent response to treatment. Analysis of CSF biogenic amines, plasma AADC levels and direct sequencing of the DDC gene was performed. CSF catecholamine metabolites were reduced, with elevation of 3-O-methyldopa. Plasma AADC activity was undetectable in both siblings, and decreased in their carrier parents. One missense mutation (853C>T) was found in exon 8, and a donor splice site mutation was found in the intron after exon 6 (IVS6+4A>T). Both siblings showed excellent response to MAO inhibitor and dopamine agonist treatment. This report expands the clinical spectrum of AADC deficiency and contributes to the knowledge of the genotype and phenotype correlation for the DDC gene. It is important to recognize the milder phenotypes of the disease as these patients might respond well to therapy.

Aromatic L-amino acid decarboxylase enzyme activity in deficient patients and heterozygotes

BACKGROUND

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive disorder characterised by developmental delay, motor retardation and autonomic dysfunction. Very low concentrations in cerebrospinal fluid (CSF) of homovanillic acid (HVA) and 5-hydroxy indole acetic acid (5-HIAA) are suggestive, but not specific, for this disorder. Confirmation of the diagnosis AADC deficiency is then required by enzyme activity measurement or genetic analysis.

METHODS

We describe assays for plasma AADC enzyme activity using both of its substrates, 5-hydroxytryptophan (5-HTP) and 3,4-dihydroxyphenylalanine (L-dopa). We measured AADC activity in controls, AADC deficient patients and heterozygotes.

RESULTS

AADC enzyme activity in control plasma on average is a factor 8-12 higher with L-dopa as substrate than with 5-HTP. Both substrates of AADC compete for the same active site of the enzyme resulting in equally decreased residual enzyme activities in AADC deficient patients. In AADC deficient patients, the enzyme activity towards both substrates, L-dopa and 5-HTP, are equally decreased, as are the CSF concentrations of HVA, 5-HIAA and MHPG, whereas heterozygotes have intermediate AADC activity levels.

CONCLUSIONS

The presently described assays for AADC activity measurement allow an efficient, reproducible and non-invasive way to confirm the diagnosis of AADC deficiency. Since AADC enzyme activity is much higher with L-dopa as a substrate, this method is to be preferred over activity measurement with 5-HTP as a substrate for diagnostic purposes.

Catecholamine toxicity in aromatic L-amino acid decarboxylase deficiency

This report presents the case of an adult male with aromatic L-amino acid decarboxylase deficiency who developed serious cardiac rhythm disturbances during treatment with intravenous dopamine and norepinephrine for severe hypotension. Three weeks later, he spontaneously developed atrial fibrillation while not receiving exogenous catecholamines. He died suddenly after several months. We presume cardiac arrhythmia was the most likely cause of his death. Patients with aromatic L-amino acid decarboxylase deficiency may be prone to cardiac arrhythmias at rest and also may be exceptionally sensitive to exogenous catecholamines. Therefore, close cardiac monitoring is indicated at baseline and during treatment with pressors.

Anesthesia management in a young child with aromatic l-amino acid decarboxylase deficiency

Aromatic l-amino acid decarboxylase (AADC) deficiency is characterized by an almost complete absence of sympathetic autoregulation, because of very low levels of circulating catecholamines. Here, we report the successful management of four consecutive anesthesia procedures in a young child presenting with AADC deficiency. Our experience suggests that, with appropriate anticipation of the potential autonomic disturbances, anesthesia, at least for minor surgical and diagnostic procedures, can be conducted safely in patients with AADC deficiency.

Aromatic l-aminoacid decarboxylase deficiency: unusual neonatal presentation and additional findings in organic acid analysis

Aromatic l-aminoacid decarboxylase (AADC) deficiency is a neurotransmitter defect leading to a combined deficiency of catecholamines and serotonin. Patients are usually detected in infancy due to developmental delay, hypotonia, and extrapyramidal movements. Diagnosis is based on an abnormal neurotransmitter metabolite profile in CSF and reduced AADC activity in plasma. An elevation of vanillactic acid (VLA) has been described as the only abnormality detected in organic acid analysis (OA) of urine. We report a patient who presented in the neonatal period with lethargy, hypotonia, metabolic acidosis, and hypoglycemia. Blood ammonia, lactic acid, and acylcarnitines were normal, but OA of a urine sample showed a small increase of VLA, raising the suspicion of AADC deficiency. The patient was lost to follow-up until the age of 8 months, when he presented with dystonia, abnormal movements, oculogyric crises, and hypothermia. Repeat OA showed not only increased levels of VLA, but also increased vanilpyruvic acid (VPA), N-acetyl-vanilalanine (AVA) and N-acetyl-tyrosine (NAT). Neurotransmitter analysis in CSF showed increased vanilalanine (1200 nmol/L, ref<100) with decreased levels of 5-hydroxy-indoleacetic acid (5-HIAA, < 5 nmol/L; ref 152-462), homovanillic acid (HVA, 83 nmol/L; ref 302-845), and methoxy-hydroxy-phenyl-glycol (<5 nmol/L; ref 51-112). AADC activity in plasma was nearly undetectable. In the urine, low excretion of vanilmandelic acid (<0.3 micromol/mmol creat; ref 0.3-20) and 5-HIAA (0.9 micromol/mmol creat; ref 4-18), was found, but HVA was normal and dopamine even elevated. This contradictory phenomenon of hyperdopaminuria has been described earlier in AADC deficient patients. We postulate that VPA and AVA could originate from vanilalanine (through a transaminase and an acetylase respectively), while NAT could originate from tyrosine through an AA acetylase. This report expands the clinical presentation of AADC deficiency and adds new markers of the disease for OA analysis, improving detection of AADC deficient patients in general metabolic screening procedures.

Aromatic L-amino acid decarboxylase deficiency: clinical features, treatment, and prognosis

BACKGROUND

Deficiency of aromatic L-amino acid decarboxylase (AADC) is associated with severe developmental delay, oculogyric crises (OGC), and autonomic dysfunction. Treatment with dopamine agonists and MAO inhibitors is beneficial, yet long-term prognosis is unclear.

OBJECTIVE

To delineate the clinical and molecular spectrum of AADC deficiency, its management, and long-term follow-up.

RESULTS

The authors present six patients with AADC deficiency and review seven cases from the literature. All patients showed reduced catecholamine metabolites and elevation of 3-O-methyldopa in CSF. Residual plasma AADC activity ranged from undetectable to 8% of normal. Mutational spectrum was heterogeneous. All patients presented with hypotonia, hypokinesia, OGC, and signs of autonomic dysfunction since early life. Diurnal fluctuation or improvement of symptoms after sleep were noted in half of the patients. Treatment response was variable. Two groups of patients were detected: Group I (five males) responded to treatment and made developmental progress. Group II (one male, five females) responded poorly to treatment, and often developed drug-induced dyskinesias.

CONCLUSIONS

The molecular and clinical spectrum of AADC deficiency is heterogeneous. Two groups, one with predominant male sex and favorable response to treatment, and the other with predominant female sex and poor response to treatment, can be discerned.

Levodopa-responsive aromatic L-amino acid decarboxylase deficiency

We report three siblings, who were treated empirically with levodopa combined with carbidopa. There was an immediate therapeutic response. Biochemical investigation surprisingly showed the clinical phenotype to be caused by aromatic L-amino acid decarboxylase deficiency. Molecular characterization showed a homozygous point mutation (c.387 G-->A) in exon 3. Kinetic studies showed the mutation to decrease the binding affinity for the substrate. This, combined with structural modeling suggesting alteration of active site configuration, provided an explanation for the therapeutic response to levodopa.

Aromatic L-amino acid decarboxylase deficiency: overview of clinical features and outcomes

In this paper, we provide a brief update of diagnostic considerations and biochemical phenotype in L-amino acid decarboxylase deficiency. We review clinical features and outcome data in 11 affected patients, including 7 previously unreported cases. All had onset of the characteristic movement disorder by 6 months of age. The phenomenology of the movement disorder is identical to that previously reported, and includes intermittent oculogyric crises and limb dystonia, generalized athetosis, and impaired voluntary movement in all patients. Autonomic dysfunction is characterized by a significant impairment of sympathetic regulation of heart rate and blood pressure, as documented via detailed studies with spectral analysis techniques in two patients. Functional clinical outcomes as a group remain poor, in spite of a variety of attempted treatment interventions, with marked impairment in motor abilities as well as in speech and communication; however, outcome was quite variable from patient to patient and covered a broad spectrum of neurological disability. Much further work remains to identify and refine the best treatment options for patients with L-amino acid decarboxylase deficiency.

Aromatic L-amino acid decarboxylase deficiency with hyperdopaminuria. Clinical and laboratory findings in response to different therapies

Aromatic L-amino acid decarboxylase (AADC - E.C. 4.1.1.28) converts L-dopa to dopamine and 5-hydroxytryptophan to serotonin. Inherited deficiency of this enzyme leads to decreased brain levels of these neurotransmitters. Clinically this results in the development of a progressive neurometabolic disorder characterized by severe hypotonia, dystonic and choreoathetoid movements, oculogyric crises, and hypothermia from infancy. Here we describe the clinical, biochemical and molecular details of two affected brothers, one of whom, despite the lack of AADC, presented with hyperdopaminuria. In addition, we detail his reactions to treatment with dopaminergic agonists, monoamine oxidase inhibitors and pyridoxine.

Clinical and laboratory findings in twins with neonatal epileptic encephalopathy mimicking aromatic L-amino acid decarboxylase deficiency

Aromatic L-amino acid decarboxylase (AADC) is a vitamin B 6 requiring enzyme involved in the biosynthesis of the neurotransmitters dopamine (DA) and serotonin. Lack of AADC leads to a combined deficiency of the catecholamines DA, norepinephrine (NE), epinephrine (E) as well as of serotonin. Here we describe premature twins who presented with severe seizures, myoclonus, rotatory eye movements and sudden clonic contractions. The patients showed an improvement of the clonic contractions under vitamin B 6 supplementation but died in the third week of life. In CSF and urine a biochemical pattern indicative of AADC deficiency was revealed. Concentrations of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) were decreased, in association with increased concentrations of 3-ortho-methyldopa (3-OMD) in CSF and significantly increased vanillactic acid in urine. The AADC enzyme substrates L-dopa and 5-hydroxytryptophan (5-HTP) were elevated in CSF. Elevated concentrations of threonine as well as of an unidentified compound in CSF rounded off the biochemical pattern. AADC activity was found to be increased in plasma and deficient in the liver. Molecular studies effectively ruled out a genetic defect in the AADC gene. The basis for the epileptic encephalopathy in the twins may be located in the metabolism of vitamin B 6 and remains to be defined.