芳香族L－アミノ酸脱炭酸酵素欠損症

Aromatic L-amino acid decarboxylase (AADC), encoded by DDC gene, catalyzes the final step in dopamine and serotonin biosynthesis. Pathogenic DDC variants cause AADC deficiency, a severe neurometabolic disorder. This study aimed to elucidate previously uninvestigated DDC variant combinations: p.Pro47Ala/p.Arg447Cys and p.Cys261Phe/p.Gly354Ser, with respect to structural and functional characteristics. Recombinant heterodimeric and homodimeric AADC proteins were expressed in Escherichia coli and purified. Enzymatic activity was quantified via ion-pair reversed-phase HPLC with photodiode detection, while structural changes were analyzed using circular dichroism and molecular modelling. Functional characterization revealed that p.Pro47Ala, p.Gly354Ser, and p.Arg447Cys homodimers showed marked loss of activity towards both L-DOPA (88%, 97% and >99%, respectively) and L-5-hydroxytryptophan (88%, 99%, >99%, respectively), whereas p.Cys261Phe retained substantial activity (82% for L-DOPA and 75% for L-5-hydroxytryptophan). Kinetic analysis indicated a mild to severe decrease in substrate affinity for all homodimers, particularly for p.Arg447Cys. Furthermore, heterodimeric combinations showed positive complementation effects on decarboxylase reaction for both heterodimers. Surprisingly, p.Cys261Phe/p.Gly354Ser also restored the wild-type activity with L-DOPA and regained 43% of L-5-hydroxytryptophan activity, whereas p.Pro47Ala/p.Arg447Cys was 15% and 10% active towards L-DOPA and L-5-hydroxytryptophan with respect to the wild-type. Our results indicate that the pathogenicity of AADC variants depends on structural combination, complementation effects in heterodimeric species, and residual activity of homodimers, highlighting the complexity of polypeptide chain interactions in compound heterozygotes.

Disorders of the phenylalanine-tyrosine-catecholamine axis are a clinically relevant group of neurometabolic conditions in which pathogenic variants in key enzymes impair dopamine and norepinephrine biosynthesis. Patients may present with movement disorders, autonomic dysfunction, developmental delay, and related neurobehavioral manifestations. In this narrative review, we synthesize the main enzymatic defects across the axis, focusing on phenylalanine hydroxylase, tyrosine hydroxylase, aromatic L-amino acid decarboxylase, and dopamine beta-hydroxylase. We describe how diagnostic practice has evolved from isolated biochemical assays to integrated approaches that link clinical phenotyping with targeted biochemical profiling and molecular confirmation. Genetic testing now supports diagnosis, treatment planning, and family counseling, while chromatographic and mass spectrometry-based methods remain essential for quantifying amino acids and neurotransmitter-related metabolites. We also discuss emerging biosensor-based strategies as a potential route to decentralized and minimally invasive monitoring.

Aromatic ʟ-amino acid decarboxylase (AADC) deficiency is a rare pediatric neurotransmitter disorder that typically necessitates lifelong care, and that carries a risk of childhood mortality. Eladocagene exuparvovec gene therapy is designed to restore AADC production. Study GT-002 (NCT04903288) is a phase 2, multicenter, open-label trial assessing the pharmacodynamics, safety, and efficacy of eladocagene exuparvovec administered to the putamen bilaterally in pediatric patients with AADC deficiency using a magnetic resonance (MR)-compatible cannula. Patients received eladocagene exuparvovec at 1.8 × 1011 vector genomes via the SmartFlow MR-compatible cannula in a single operative session. Endpoints include the change from baseline in cerebrospinal fluid homovanillic acid levels, motor milestone achievement, and safety. Here we report results from 48 weeks of follow-up. Mean (SD) cerebrospinal fluid homovanillic acid levels increased from baseline (22.5 [32.3] nmol/L; n = 13) to week 48 (55.3 [45.6] nmol/L; change from baseline: 28.3 [13.7] nmol/L; p = 0.0003; n = 9), indicating de novo dopamine production. At baseline (n = 13), all patients showed severe motor developmental delay; at week 48 (n = 12), nine achieved full head control, four could sit unassisted, two could stand with support, and two could walk independently to a toy. Overall, 260 treatment-emergent adverse events were reported in 13 patients; 259 were deemed unrelated and one likely unrelated to the MR-compatible cannula. No treatment-emergent adverse events led to study withdrawal and no deaths occurred. This study provides further evidence of the favorable pharmacodynamic, efficacy, and safety profile of eladocagene exuparvovec in children with AADC deficiency; intraputaminal administration using an MR-compatible cannula was well tolerated. Study GT-002 (NCT04903288) provides further evidence of the favourable pharmacodynamic, efficacy and safety profile of eladocagene exuparvovec gene therapy in children with AADC deficiency over 48 weeks and demonstrates that intraputaminal administration using an MR-compatible cannula was well tolerated, allowing for real-time MRI confirmation of cannula placement and infusate coverage, and for accurate dosing to the putamen.

Adeno-associated virus (AAV) vectors have taken center stage for gene therapy and have shown clinical efficacy in 15 human diseases to date. The Food and Drug Administration has approved seven AAV "drugs" for one-time treatment respectively for Leber's congenital amaurosis, spinal muscular atrophy, hemophilia B, Duchenne muscular dystrophy, hemophilia A, and aromatic L-amino acid decarboxylase deficiency. Despite these remarkable developments, it has become increasingly clear that the first generation of AAV vectors is less than optimal since in most, if not all, cases, exceedingly high doses are needed to achieve clinical efficacy, and as a consequence, in some patients, serious adverse events have been observed, and to date, at least 21 patients have died. Thus, there is a need to reassess the limitations of the first generation of AAV vectors as well as an urgent need to develop the next generation of AAV vectors that are safe and effective.

PURPOSE: We present two clinical cases of frameless, neuronavigated gene therapy with eladocagene exuparvovec for aromatic L-amino acid decarboxylase (AADC) deficiency in pediatric patients, detailing the targeted bilateral microdose delivery of viral vectors into the putamen and highlighting the feasibility and challenges of this approach in managing a rare neurometabolic disorder. METHODS: Two patients with a confirmed diagnosis of AADCD underwent frameless stereotactic gene therapy. High-resolution 3 T MRI-guided trajectories were planned for the targeted bilateral putaminal infusion of 0.32 ml of eladocagene exuparvovec (AAV2-hAADC). The agent was delivered via a SmartFlow Neuro Ventricular Cannula in a "Z-pattern," retracting the cannula 2 mm every 9 min to achieve controlled microdosing. RESULTS: Accurate frameless drug delivery was achieved in a shorter time than frame-based approaches, with no intraoperative or postoperative complications. One patient showed a small post-ischemic cyst on the 1-month follow-up MRI, without any neurological deficits. Over 2 months, both patients demonstrated reduced oculogyric crises, diminished hyperkinesis, and improved head control, with no significant adverse events. CONCLUSION: Frameless, neuronavigated gene therapy for AADC deficiency proved both feasible and safe, with early clinical improvements observed in motor function and symptom control. This technique offers a promising alternative to frame-based methods and expands treatment options for this rare neurometabolic disorder.