For years, parents of a Texas boy believed he was mostly nonverbal because of a brain aneurysm he had when he was 10 days old.

The boy, Mason Motz, 6, of Katy, Tex., started going to speech therapy when he was 1. In addition to his difficulties speaking, he was given a diagnosis of Sotos syndrome, a disorder that can cause learning disabilities or delayed development, according to the National Institutes of Health.

His parents, Dalan and Meredith Motz, became used to how their son communicated.

“He could pronounce the beginning of the word but would utter the end of the word,” Ms. Motz said in an interview. “My husband and I were the only ones that could understand him.”

That all changed in May 2017, when Dr. Amy Luedemann-Lazar, a pediatric dentist, was performing several procedures on Mason’s teeth. She noticed that his lingual frenulum, the band of tissue under his tongue, was shorter than is typical and was attached close to the tip of his tongue, keeping him from moving it freely.