“Mr. and Mrs. Smith, we finally have an answer for you.” The couple, whose real names we are protecting for privacy, looked at me anxiously. I had been evaluating their young daughter, Sally, in my role as a medical geneticist at the Children’s Hospital at Montefiore in the Bronx, a borough of New York City. For years, the Smiths had been searching to learn why Sally was suffering from epilepsy, why she didn’t seem to understand them and why she wasn’t speaking at 6 years of age. In 2021, they ended up in my clinic.
I decided to send a sample of Sally’s blood for whole-exome sequencing, a test that could identify a change in one of her genes that might be responsible for her symptoms. A few weeks later I had the answer.
“Sally has an extremely rare disorder that you’ve probably never heard of,” I told them. “It’s so rare that it doesn’t even have a real name yet. It’s called NAA10-related disorder.” The family looked at me with blank stares. I took a deep breath and continued.
The NAA10 gene codes for an enzyme that modifies critical proteins, enabling them to function properly. A single change in Sally’s NAA10 gene would cause the enzyme to be made incorrectly, resulting in intellectual disability and seizures. The NAA10 gene is located on the X chromosome, which is one of two sex chromosomes in humans.
Males typically carry an X and a Y chromosome, while females usually have two X chromosomes; as a result, boys are usually more severely affected and girls have a less predictable course. I explained to the family that only about 50 other people with NAA10-related disorder have been reported across the globe. They then asked me about treatment. I replied sadly, “none.” I could see them struggling to wrap their heads around this.
They asked further questions about what might happen to Sally: Will she learn to speak? Will she be able to learn? Will she grow old? I told them that there is not enough experience to accurately predict what Sally’s future will look like. Feeling useless, I said, “Here is a patient support group that might be helpful.” And with nothing more to offer, I added: “I’ll see you in a year.”
Moments like this – a long-awaited answer that is met with more bewilderment than relief – are not uncommon in the practice of medical genetics. Most people expect that after a long, frustrating search, finding the underlying diagnosis will provide answers and a path forward. But sometimes, in cases like Sally’s, the answer simply begets more questions.
We’ve faced these difficult questions as two researchers with decades of experience in rare genetic diseases. One of us is a medical geneticist whose clinical work focuses on the diagnosis and management of individuals with rare genetic disorders; the other is a neuroscientist working to determine how rare genetic diseases impact brain function and possible ways to correct them.