A new treatment came too late to save my daughter. I celebrate it anyway.

Recently, the Food and Drug Administration approved the first gene therapy to treat a fatal childhood inherited brain disease called metachromatic leukodystrophy (MLD).

You might expect that I — the mother of a child who died from MLD before this treatment became available — would be bitter.

But you would be wrong.

On July 5, 2012, a neurologist at Children’s Hospital of Philadelphia told my husband and me that our 2-year-old daughter, Calliope, was dying. Genetic testing confirmed she had MLD, a rare neurological disorder that destroys the brain’s white matter.

That day marked the beginning of my crash course in one of the worst diseases you’ve never heard of. If ALS (also known as Lou Gehrig’s disease) and Alzheimer’s created an offspring that targeted toddlers, it would look something like MLD.

Babies with MLD are born with a faulty gene that leaves them unable to produce an enzyme needed to break down fatty substances called sulfatides. The buildup of them eventually becomes toxic to nerves, leading to progressive loss of cognition and movement.

By the time symptoms appear, it is already too late.

Soon after developing symptoms, babies with MLD lose almost all function. In Cal’s case, it took her only two short months after her diagnosis to lose the ability to walk, speak, feed herself, or sit unaided. From there, the disease progresses quickly, causing children to lapse into a vegetative state.

The diagnosis came with no hope. Not only was there no treatment for MLD, but we learned that Cal would suffer terribly as her neurons died. And she was unlikely to live past her 6th birthday.

The only tangible thing our doctor could offer us was a Make-A-Wish vacation. We went to Martha’s Vineyard; Cal loved the ocean.

Just a few days short of the one-year anniversary of Cal’s diagnosis, a team of researchers in Milan announced that they had successfully treated three babies with MLD using a gene therapy. The doctors wiped out the babies’ immune systems, then infused them with stem cells that had been “infected” with a working copy of the faulty gene.

Even as I watched my darling daughter slowly die, I found my purpose: I established a foundation in her honor and began raising money for MLD, one cupcake sale at a time.

If I couldn’t save Cal, I was determined to save as many other children as possible.

Over nearly a decade, the Calliope Joy Foundation has sold 45,000 cupcakes and raised nearly $1 million. We used that money to send 20 children with MLD to Italy to receive the gene therapy. The first patient we sponsored is now a beautiful, healthy 10-year-old who has no idea she was supposed to become paralyzed, nonverbal, and dependent on a feeding tube.

For me and other families of children who have MLD, the news of the FDA’s approval of the new treatment, Lenmeldy, is cause for rejoicing. For the first time since this disease so cruelly reshaped my family, I can say these words aloud: There is an FDA-approved therapy for MLD.

And what Lenmeldy does is nothing short of miraculous. In a trial of its effectiveness, all children who received Lenmeldy were alive at 6 years of age, relative to only half of those who didn’t receive it. Most of the treated children could walk without any help and had normal language skills.

And yet, while I celebrate with the families whose children have received this miraculous treatment, a hot coal of grief remains lodged in my throat: For my family, for my daughter, this happy news came too late.

The FDA approval of Lenmeldy coincides almost precisely with the two-year anniversary of Cal’s death. If only she had been born just a little bit later, she would still be alive.

If only she had been born just a little bit later, she would still be alive.

At this strange juncture, I find myself overcome with a range of emotions. It seems odd that a grieving mother can hold so many paradoxical feelings. And yet, when you champion a cause because you have lost a child, you find solace in strangers’ miracles.

Since losing Cal, I have dreamed of meeting a 14-year-old girl with curly brown hair and brown eyes. She adores Taylor Swift and wears Nike Air Jordans. She teases her older brother and sister and drives her mother crazy. She has a huge, exciting life ahead of her.

I have accepted that this girl is not my daughter Cal. It is enough to know that this girl lives because of my Cal.

Maria Kefalas is a professor at St. Joseph’s University in Philadelphia. She is the founder of the Calliope Joy Foundation and Cure MLD. Her latest book is a memoir titled “Harnessing Grief.”