Childhood epilepsies were once a medical mystery. Now, several kinds of treatments hold promise.

Fifteen years ago, scientists had no idea what caused a series of rare childhood diseases that are characterized by epileptic seizures and neurodevelopmental delays.

With the advent of widespread genetic testing, they now know the cause of more than 100, said Ingo Helbig, a neurologist at Children’s Hospital of Philadelphia.

Helbig is the co-director of a new center for studying these diseases, established with a $25 million gift from an anonymous donor in February. He is joined by CHOP colleague Beverly Davidson and University of Pennsylvania scientist Ben Prosser, whose daughter was born with one of these diseases, STXBP1 encephalopathy.

Though rare on their own, collectively these conditions occur in more than 10,000 babies born each year in the U.S., Helbig said.

Within the next few years, several kinds of emerging therapies may prove useful in treating many of them, he and Davidson said.

» READ MORE: A scientist’s daughter was born with a rare disease, so he began to study it. An anonymous donor just chipped in $25 million.

Here are the basics on two such strategies:

The human genome consists of roughly 30,000 genes, and people are born with two copies of each. At the new center at Penn and CHOP, scientists will study neurological diseases caused by mutations in a single copy of a given gene.

Researchers hope to treat some of the conditions with gene therapy, replacing the flawed copy of the gene in question with a normal one.

Typically, these replacement genes are administered to the patient by means of a viral “vector” — a type of benign, inactivated virus that carries the beneficial gene as its cargo.

The first such therapy, made by Philadelphia-based Spark Therapeutics to treat a rare form of blindness, was approved by the FDA in 2017. Another was approved in 2022 for treating the bleeding disorder hemophilia B, made by CSL Behring, which has U.S. offices in King of Prussia.

Gene therapies can be expensive, with the price to treat one patient as high as the low millions. But advocates argue that when these one-time therapies are successful, they allow patients to avoid a lifetime’s worth of other medical costs.

Another type of therapy to be studied at the joint Penn-CHOP center is a tongue-twister, involving short synthetic stretches of genetic material called antisense oligonucleotides (ASO).

ASOs can be used to modify how critical proteins are made and used inside human cells.

In the case of STXBP1 — the disease affecting the daughter of Prosser, the Penn scientist — ASOs would be used to extend the shelf-life of proteins made from the recipe contained in a patient’s “good” copy of that gene. Unlike a one-and-done gene therapy, it would have to be administered multiple times a year, via spinal tap.

One type of ASO approved by the FDA is called Spinraza, made by Carlsbad, Calif.-based Ionis Pharmaceuticals for treating a rare disorder called spinal muscular atrophy.