Doctors can now use a person’s genetic sequence as the basis for rational drug selection—a sign of how far personalized genomics has come in recent years. A case report published today in the New England Journal of Medicine illustrates the strength of this approach.
The paper describes an extended Saudi Arabian family in which many young siblings suffered from a Parkinson’s-like condition affecting their movement. The children had normal levels of neurotransmitters dopamine and serotonin in their spinal fluid, suggesting they should have been healthy. The unique circumstances prompted researchers to use the latest advances in genomic sequencing to identify a mutation in the SLC18A2 gene, which encodes the protein vesicular monoamine transporter 2, or VMAT2, as the cause of the disease.
A team led by Berge Minassian, a neurologist at the Hospital for Sick Children in Toronto, successfully pinpointed the mutation and treated the symptoms in these siblings. “I am certain that in the next few years patients walking into children’s hospitals will have their whole genomes sequenced,” says Minassian. Until now, magnetic resonance imaging (MRI) has been the primary diagnostic tool for people with neurological diseases.
The study’s initial patient was a 16-year-old girl first diagnosed with muscle weakness when she was just four months old. She sat for the first time when she was two and a half years old, began crawling at four and walking—and only with difficulty—at the very late age of 13. Her symptoms resembled Parkinson’s disease, but all her metabolic and MRI tests came back normal. Doctors also ran tests on her 2-year-old sister who suffered from similar symptoms and a red flag showed up in the toddler’s urine, where dopamine levels were below average. The physicians then gave the 16-year-old and her three younger siblings levodopa-carbidopa, a dopamine precursor used to treat Parkinson’s. They were puzzled, though, when the conditions worsened in all four.
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