I would like to thank the American Association of Neurological Surgeons for the opportunity to present this work at the 2020 annual scientific meeting. The title of this presentation is Gene Therapy for the Treatment of Primary L Aromatic Amino Acid Decarboxylase Deficiency in Children. Disclosures for this presentation include funding by the NIH and NDS, which supported the study reported. The presenter has unrelated funding from the Chad Tuff Foundation and the V Foundation. Primary AADC deficiency is a genetic disorder autosomal recessive, which is caused by mutations in the AADC gene. The condition is rare and presents in infants. The diagnosis is made by specific abnormalities in CSF metabolites, plasma AADC activity, and by genetic testing. The clinical manifestations of the condition include hypotonia and profound motor delay, as well as involuntary movements. The non-motor manifestations include autonomic disturbances, emotional lability, cognitive impairment, sleep disturbances. There are limited treatment options, and dopaminergic therapy has poor responses. As demonstrated by this biochemical pathway, the loss of function of the AADC enzyme results in an inability to metabolize L-DOPA to dopamine, and as well there is a deficiency of the serotonergic pathway as well. The canonical pathway from the midbrain is to the striatum through the nigrostriatal pathway, but it should be noted that there are additional dopaminergic pathways to the mesolimbic system, the amygdala, hippocampus, as well as the prefrontal regions. These are believed to be involved in motivation and emotion, pleasure, reward, and goal-directed behavior. The purpose of the study was to examine two key hypotheses that delivery of a adenovirus vector encoding a normal AADC gene to the substantia nigra compacta and the ventral tegmental area will use existing axonal projections to achieve correction of dopaminergic signaling. In addition, we felt that the physiologic expression of AADC in these pathways was more appropriate than a putamenal target. The clinical hypothesis is that midbrain expression of AADC will result in improvements in motor milestones, gross and fine motor function, as well as dystonia and overall quality. The aims of the phase 1-2 study, the primary aims include an assessment of safety, as well as an assessment of post gene therapy dyskinesia, sleep disturbance, mood disturbance, and adverse events. Secondary aims include an assessment of efficacy, as well as measurement of biomarkers such as CSF neurotransmitters, F-DOPA PET, and an assessment of symptoms such as oculogyric crises, sleep, mood, and motor function. The overall study was planned as a two-stage study. The results in this presentation involve stage one, which includes initially six subjects, but was expanded to seven subjects. There were two groups, which was a low and high dose group, which included subjects treated with 8.3 times 10 to the 11th viral genomes versus 2.6 times 10 to the 12th viral genomes. As noted, there were seven subjects overall in this cohort, four female, three male. They were all young, between four to nine years of age. All patients had severe motor disability, and as noted, these patients were separated into two groups with an overall difference in the total viral genome. The patients were treated using an intraoperative MRI suite to determine both location of the catheter, as well as the distribution of the infusate. Patients underwent a bicoronal incision, as well as a preoperative assessment of the trajectory and approach to the midbrain. They were transferred to the intraoperative suite, where the ClearPoint system was used for both targeting and localization of the targets. Using the ClearPoint system mounted on the subjects' calvarium, a catheter was placed into the preselected targets and used for infusion into those targets. In this situation, in this illustration, the volume of distribution is described or demonstrated in both sides, right and left, in the substantia nigra compacta and the ventral tegmental area. The ratio of volume of distribution to volume of infusion was approximately 3.3. Of the seven subjects treated in this cohort, one patient or one subject died six months after gene therapy. The patient was otherwise doing well and had improvement in clinical function. The patient was not symptomatic prior to the event. An autopsy was declined, so the exact cause of mortality was not clear, but was not felt to be directly related to the study interventions. With respect to adverse events, the overall procedure and treatment was extremely well tolerated. There were two patients that experienced hypoglycemia, and this was felt that this was due to both anesthesia and the patients being NPO prior to the procedure. Otherwise, no other significant adverse events were noted. Patients were, after treatment, were noted to have dyskinesia. There was increased measurement of dopamine metabolites in the CSF that was obtained at serial time points. These increased and then plateaued after approximately six months after gene therapy treatment. The GM-FM88 scale was used to measure overall gross motor function. Most patients or subjects started at a very low level of functioning and then increased over the next several months after gene therapy, with several subjects demonstrating marked improvement in gross motor function. There were substantial improvements in both sleep and behavior, with patients demonstrating improvement in ability to sleep through the night and improvement in irritability. A characteristic feature of the condition are oculogyric crises, which involve involuntary movements of the eyes and head, and all subjects demonstrated some improvement, with six of seven subjects demonstrating marked improvement in oculogyric crises, with only mild crises being noted after approximately three months following gene therapy. The surgical delivery of the AAV vector into the brainstem confirmed that the nigrostriatal distribution from this area resulted in evidence of increase in F-dopa PET signal in the putamen, but also in the frontal and parietal areas of the brain. This confirmed that there were broader areas of distribution of the dopaminergic pathways in regions beyond the putamen. Subject 2 demonstrated a clear increase in the signal in the putamen, as shown in these figures. The conclusions of the study are that midbrain delivery of adenovirus encoding the AADC gene can be performed safely. There were no serious adverse events related to the surgical procedure. There was one mortality which was not felt to be related to the experimental intervention. There were increases in CSF markers, as well as F-dopa PET, and patients experienced a significant clinical improvement in oculogyric crises, motor function, and non-motor symptoms. Acknowledgements are noted by the study team at UCSF, Ohio State University, and funding by the National Institutes of Health.

gene therapy

Primary L Aromatic Amino Acid Decarboxylase deficiency

AADC deficiency

motor delays

cognitive impairment