Long-Term Outcomes of Eladocagene Exuparvovec Compared with Standard of Care in Aromatic L-Amino Acid Decarboxylase (AADC) Deficiency: A Modelling Study

INTRODUCTION

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare disease with symptoms including movement disorders, developmental delays, and autonomic symptoms starting from birth; further, patients with AADC deficiency are at a high risk of death in the first decade of life. Limited information on the impact of treatment with gene therapy on patients' disease trajectories and survival, quality-of-life, and resource usage benefits are available.

METHOD

A cohort-based model with a lifetime horizon has been developed, based on motor milestones, to estimate the long-term benefits for patients after treatment with eladocagene exuparvovec compared to best supportive care (BSC). The model takes a National Health Service (NHS) perspective using a UK setting. The model comprises two parts: the developmental phase, in which patients with initially no motor function can progress to other motor milestone states, and a long-term projection phase. Efficacy for eladocagene exuparvovec is derived from clinical trial data with a duration up to 120 months. As the incidence of AADC deficiency is low, data for key model inputs is lacking; therefore estimates of survival by motor milestone were based on proxy diseases. A disease-specific utility study provided quality of life inputs and a burden of illness study informed inputs for disease management.

RESULTS

The model indicates survival (25.25 undiscounted life years gained) and quality-of-life benefits (20.21 undiscounted quality-adjusted life years [QALYs] gained) for patients treated with eladocagene exuparvovec compared to BSC. Resource usage costs are greater for patients treated with eladocagene exuparvovec, mainly due to the increased life expectancy during which patients accrue additional healthcare resource usage. Scenario analyses indicate robust results.

CONCLUSION

This study assessed long-term outcomes for patients with AADC deficiency. Patients treated with eladocagene exuparvovec were found to have improved survival and quality of life benefits compared to patients treated with BSC.

Catecholamines and Parkinson's disease: tyrosine hydroxylase (TH) over tetrahydrobiopterin (BH4) and GTP cyclohydrolase I (GCH1) to cytokines, neuromelanin, and gene therapy: a historical overview

The author identified the genes and proteins of human enzymes involved in the biosynthesis of catecholamines (dopamine, norepinephrine, epinephrine) and tetrahydrobiopterin (BH4): tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine β-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), and GTP cyclohydrolase I (GCH1). In Parkinson's disease (PD), the activities and levels of mRNA and protein of all catecholamine-synthesizing enzymes are decreased, especially in dopamine neurons in the substantia nigra. Hereditary GCH1 deficiency results in reductions in the levels of BH4 and the activities of TH, causing decreases in dopamine levels. Severe deficiencies in GCH1 or TH cause severe decreases in dopamine levels leading to severe neurological symptoms, whereas mild decreases in TH activity in mild GCH1 deficiency or in mild TH deficiency result in only modest reductions in dopamine levels and symptoms of DOPA-responsive dystonia (DRD, Segawa disease) or juvenile Parkinsonism. DRD is a treatable disease and small doses of L-DOPA can halt progression. The death of dopamine neurons in PD in the substantia nigra may be related to (i) inflammatory effect of extra neuronal neuromelanin, (ii) inflammatory cytokines which are produced by activated microglia, (iii) decreased levels of BDNF, and/or (iv) increased levels of apoptosis-related factors. This review also discusses progress in gene therapies for the treatment of PD, and of GCH1, TH and AADC deficiencies, by transfection of TH, AADC, and GCH1 via adeno-associated virus (AAV) vectors.

Mild Aromatic L-Amino Acid Decarboxylase Deficiency: As A Reason For Hypoketotic Hypoglycemia In A 4-Year-Old Girl

Aromatic L-amino acid decarboxylase (AADC) deficiency is a disease in which neurological findings are dominant due to deficiencies in neurotransmitter synthesis; hypoglycemia caused by autonomic dysfunction is one of the symptoms that may be encountered. Here we report a mild AADC deficiency presenting with hypoglycemia without a neurological sign. A 4-year-old girl presented with recurrent hypoglycemia. Her growth and development were normal. Plasma insulin and cortisol values were normal in the sample at the time of hypoglycemia. The C8:1-Carnitine elevation was detected in the acylcarnitine profile. The clinic exome panel was performed with the suggestion of a fatty acid oxidation defect. However, a homozygous variant in the DDC gene was detected. On top of that, CSF neurotransmitter analysis revealed low 5-hydroxy indol acetic ( 5 HIAA ) and homovanillic acid ( HVA ) and high 3-O-methyl-dopa and methyltetrahydrofolate ( 5 MTHF ) consistent with AADC deficiency. Plasma AADC enzyme activity was low. The episodes of hypoglycemia were treated with uncooked cornstarch. Our case emphasizes that AADC deficiency should be considered in patients with hypoglycemia.

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.

Symptoms and impact of aromatic l-amino acid decarboxylase (AADC) deficiency: a qualitative study and the development of a patient-centred conceptual model

BACKGROUND

Aromatic l-amino acid decarboxylase (AADC) deficiency is a rare neurological condition, with an estimated global prevalence of 1:32,000 to 1:90,000 live births. AADC deficiency is associated with a range of symptoms and functional impairments, but these have not previously been explored qualitatively. This study aimed to understand the symptoms of AADC deficiency and its impact on individuals' health-related quality of life.

METHODS

Qualitative interviews were conducted with caregivers of individuals with AADC deficiency in Italy, Spain, Portugal and the United States. An interview guide was developed with input from clinical experts and caregivers, and explored the symptoms and impacts of AADC deficiency. Interviews were conducted by telephone and were recorded and transcribed. Data were analysed using thematic analysis and saturation was recorded.

RESULTS

Fourteen caregivers took part, who provided care to 13 individuals with AADC deficiency aged 1-15 years. All individuals had impaired motor function, which was attributed to low muscle tone and muscle weakness. The level of motor function varied considerably, ranging from no motor function (no head control) to being able to take a few steps without support. Other impairments included cognitive impairment, communication difficulties, movement disorders (e.g. oculogyric crises), gastrointestinal symptoms, eating difficulties, fatigue and sleep disruption. Most individuals were completely dependent on their caregivers for all aspects of their lives. This limited function had a negative impact on their ability to socialise with their peers and on their emotional wellbeing. These concepts and relationships are illustrated in a conceptual model, and moderating factors (e.g. physiotherapy and medication) are discussed.

CONCLUSION

This is the first qualitative study to report on the experience of living with AADC deficiency. Caregivers report individuals with AADC deficiency experience a wide range of symptoms and functional impairments, which have a substantial impact on their health-related quality of life.

Evaluation of 3-O-methyldopa as a biomarker for aromatic L-amino acid decarboxylase deficiency in 7 Brazilian cases

Aromatic L-amino acid decarboxylase (AADCD) deficiency is an autosomal recessive neurometabolic disorder, caused by biallelic mutations in the DDC gene, that impairs the synthesis or metabolism of neurotransmitters leading to severe motor dysfunction. The main clinical signs are oculogyric crisis, hypotonia, hypokinesia, and dystonia. The biochemical diagnosis can be performed in cerebrospinal fluid by neurotransmitter analysis, which requires an invasive lumbar puncture, and the sample needs to be shipped frozen to a reference laboratory, usually across a country border. Measurement of AADC activity in plasma is also possible, but available in a few labs globally. 3-O-methyldopa (3-OMD) is a catabolic product of L-dopa and it is elevated in patients with AADC deficiency. The quantification of 3-OMD can be performed in dried blood spots (DBS), a sample that could be shipped at room temperature. 3-OMD levels of AADCD patients and controls were quantified in DBS by liquid chromatography tandem mass spectrometry. DBS samples from 7 Brazilian patients previously diagnosed with AADCD were used to validate the 3-OMD quantification as a screening procedure for this condition. All AADCD patients had at least a four-fold increase of 3-OMD. Thus, 3-OMD seems to be a reliable marker for AADCD, with potential use also in the newborn screening of this disease.

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.

Blood, urine and cerebrospinal fluid analysis in TH and AADC deficiency and the effect of treatment

Background

Aromatic L-amino acid decarboxylase (AADC) deficiency and tyrosine hydroxylase (TH) deficiency are rare inherited disorders of monoamine neurotransmitter synthesis which are typically diagnosed using cerebrospinal fluid examination of monoamine neurotransmitter metabolites. Until now, it has not been systematically studied whether analysis of monamine neurotransmitter metabolites in blood or urine has diagnostic value as compared to cerebrospinal fluid examination, or whether monoamine neurotransmitter metabolites in these peripheral body fluids is useful to monitor treatment efficacy.

Methods

Assessment, both by literature review and retrospective analysis of our local university hospital database, of monoamine neurotransmitter metabolites in urine, blood and cerebrospinal fluid, and serum prolactin levels, before and during treatment in patients with AADC and TH deficiency.

Results

In AADC deficiency, 3-O-methyldopa in serum or dried blood spots was reported in 34 patients and found to be (strongly) increased in all, serotonin in serum was decreased in 7/7 patients. Serum prolactin was increased in 34/37 and normal in 3 untreated patients. In urine, dopamine was normal or increased in 21/24 patients, 5-hydroxyindoleacetic acid was decreased in 9/10 patients, and vanillactic acid was increased in 19/20 patients. No significant changes were seen in monoamine neurotransmitter metabolites after medical treatment, except for an increase of homovanillic acid in urine and cerebrospinal fluid after levodopa therapy, sometimes even in absence of a clinical response. After gene therapy, cerebrospinal fluid homovanillic acid increased in most patients (8/12), but 5-hydroxyindoleacetic acid remained unchanged in 9/12 patients.

In TH deficiency, serum prolactin was increased in 12/14 and normal in the remaining untreated patients. Urinary dopamine was decreased in 2/8 patients and normal in 6. Homovanillic acid concentrations in cerebrospinal fluid increased upon levodopa treatment, even in the absence of a clear treatment response.

Conclusions

This study confirms that cerebrospinal fluid is the most informative body fluid to measure monoamine neurotransmitter metabolites when AADC or TH deficiency is suspected, and that routine follow-up of cerebrospinal fluid measurements to estimate treatment response is not needed. 3-O-methyldopa in dried blood spots and vanillactic acid in urine are promising peripheral biomarkers for diagnosis of AADC deficiency. However, in many patients with TH or AADC deficiency dopamine in urine is normal or increased thereby not reflecting the metabolic block. The value of serum prolactin for follow-up of AADC and TH deficiency should be further studied.

Aromatic L-amino Acid Decarboxylase (AADC) deficiency: results from an Italian modified Delphi consensus

BACKGROUND

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare and underdiagnosed neurometabolic disorder resulting in a complex neurological and non-neurological phenotype, posing diagnostic challenges resulting in diagnostic delay. Due to the low number of patients, gathering high-quality scientific evidence on diagnosis and treatment is difficult. Additionally, based on the estimated prevalence, the number of undiagnosed patients is likely to be high.

METHODS

Italian experts in AADC deficiency formed a steering committee to engage clinicians in a modified Delphi consensus to promote discussion, and support research, dissemination and awareness on this disorder. Five experts in the field elaborated six main topics, each subdivided into 4 statements and invited 13 clinicians to give their anonymous feedback.

RESULTS

100% of the statements were answered and a consensus was reached at the first round. This enabled the steering committee to acknowledge high rates of agreement between experts on clinical presentation, phenotypes, diagnostic work-up and treatment strategies. A research gap was identified in the lack of standardized cognitive and motor outcome data. The need for setting up an Italian working group and a patients' association, together with the dissemination of knowledge inside and outside scientific societies in multiple medical disciplines were recognized as critical lines of intervention.

CONCLUSIONS

The panel expressed consensus with high rates of agreement on a series of statements paving the way to disseminate clear messages concerning disease presentation, diagnosis and treatment and strategic interventions to disseminate knowledge at different levels. Future lines of research were also identified.

Aromatic L-Amino acid decarboxylase deficiency: A new case from Turkey with a novel mutation

Aromatic L-amino acid decarboxylase (AADC), a vitamin B6-requiring enzyme that converts L-dopa to dopamine and 5-hydroxytryptophan to serotonin. Deficiency of this enzyme results in developmental delay, muscular hypotonia, dystonia, involuntary movements, autonomic dysfunction, and oculogyric crises. We now report a 2-year-old Turkish boy with AADC deficiency confirmed by greatly reduced AADC activity in the plasma and by genetic studies. Mutation analysis revealed a homozygous mutation c.208C > T (p. His70Tyr) in exon 3 of the AADC gene which has not been described to date.