Mucopolysaccharidosis type IIIA is a severe degenerative disease caused by an autosomal recessive defect of a gene encoding a lysosomal heparan-N-
sulfamidase, the N-sulfoglycosamine sulfohydrolase (SGSH), the catalytic site of which is activated by a
sulfatase-modifying factor (SUMF1). Four children (Patients 1-3, aged between 5.5 and 6 years; Patient 4 aged 2 years 8 months) received intracerebral
injections of an adeno-associated viral vector serotype rh.10-SGSH-IRES-SUMF1 vector in a phase I/II clinical trial. All children were able to walk, but their cognitive abilities were abnormal and had declined (Patients 1-3). Patients 1-3 presented with brain
atrophy. The therapeutic vector was delivered in a frameless stereotaxic device, at a dose of 7.2×10(11) viral genomes/patient simultaneously via 12 needles as deposits of 60 μl over a period of 2 hr. The vector was delivered bilaterally to the white matter anterior, medial, and posterior to the basal ganglia. Immunosuppressive treatment (
mycophenolate mofetil and
tacrolimus) was initiated 15 days before surgery and maintained for 8 weeks (
mycophenolate mofetil) or throughout follow-up (
tacrolimus, with progressive
dose reduction) to prevent elimination of transduced cells. Safety data collected from inclusion, during the neurosurgery period and over the year of follow-up, showed good tolerance, absence of adverse events related to the injected product, no increase in the number of infectious events, and no
biological sign of toxicity related to immunosuppressive drugs. Efficacy analysis was necessarily preliminary in this phase I/II trial on four children, in the absence of validated
surrogate markers. Brain
atrophy evaluated by magnetic resonance imaging seemed to be stable in Patients 1 and 3 but tended to increase in Patients 2 and 4. Neuropsychological evaluations suggested a possible although moderate improvement in behavior, attention, and sleep in Patients 1-3. The youngest patient was the most likely to display neurocognitive benefit.