A new study published in Nature Communications suggests that gene therapy delivered into the brain may be safe and effective in treating aromatic L-amino acid decarboxylase (AADC) deficiency. AADC deficiency is a rare neurological disorder that develops in infancy and leads to near absent levels of certain brain chemicals, serotonin and dopamine, that are critical for movement, behavior, and sleep.
Children with the disorder have severe developmental, mood dysfunction including irritability, and motor disabilities including problems with talking and walking as well as sleep disturbances. Worldwide there have been approximately 135 cases of this disease reported.
In the study, led by Krystof Bankiewicz, M.D., Ph.D., professor of neurological surgery at Ohio State College of Medicine in Columbus, and his colleagues, seven children received infusions of the DDC gene that was packaged in an adenovirus for delivery into brain cells. The DDC gene is incorporated into the cells' DNA and provides instructions for the cell to make AADC, the enzyme that is necessary to produce serotonin and dopamine. The research team used magnetic resonance imaging to guide the accurate placement of the gene therapy into two specific areas of the midbrain.
Positron emission tomography (PET) scans performed three and 24 months after the surgery revealed that the gene therapy led to the production of dopamine in the deep brain structures involved in motor control. In addition, levels of a dopamine metabolite significantly increased in the spinal fluid.
The therapy resulted in clinical improvement of symptoms. Oculogyric crises, abnormal upward movements of the eyeballs, often with involuntary movements of the head, neck and body, that can last for hours and are a hallmark of the disease, completely went away in 6 of 7 participants. In some of the children, improvement was seen as early as nine days after treatment. One participant continued to experience oculogyric crises, but they were less frequent and severe.
All of the children exhibited improvements in movement and motor function. Following the surgery, parents of a majority of participants reported their children were sleeping better and mood disturbances, including irritability, had improved. Progress was also observed in feeding behavior, the ability to sit independently, and in speaking. Two of the children were able to walk with support within 18 months after receiving the gene therapy.
The gene therapy was well tolerated by all participants and no adverse side effects were reported. At three to four weeks following surgery, all participants exhibited irritability, sleep problems, and involuntary movements, but those effects were temporary. One of the children died unexpectedly seven months after the surgery. The cause of death was unknown but assessed to be due to the underlying primary disease.
Pearson, T.S., et al. (2021) Gene therapy for aromatic L-amino acid decarboxylase deficiency by MR-guided direct delivery of AAV2-AADC to midbrain dopaminergic neurons. Nature Communications. doi.org/10.1038/s41467-021-24524-8.