Tongue-tie happens when a small band of tissue under a baby’s tongue, called the lingual frenulum, doesn’t thin out and recede the way it normally would during early fetal development. Between 1.7% and 10.7% of newborns are diagnosed with the condition, and the wide range reflects genuine disagreement about where normal variation ends and a true tongue-tie begins.
How Tongue-Tie Develops Before Birth
During the first trimester of pregnancy, a baby’s tongue initially forms fused to the floor of the mouth. As development progresses, cells along that connecting tissue are programmed to die off in a process called apoptosis, gradually freeing the tongue to move independently. When that programmed cell death doesn’t happen completely, too much tissue remains. The leftover frenulum keeps the tongue tethered to the floor of the mouth, restricting its range of motion.
This isn’t something caused by anything a parent did or didn’t do during pregnancy. It’s a glitch in a tightly choreographed developmental sequence that plays out very early, often before many people even know they’re pregnant.
Genetics and Family History
Tongue-tie runs in families. In one pedigree study of 149 patients, about 39% had at least one relative with the same condition. Several specific genes have been identified as contributors. The most well-established is TBX22, a gene on the X chromosome. Mutations in this gene cause non-syndromic tongue-tie and are also linked to X-linked cleft palate. Because TBX22 sits on the X chromosome, boys are more commonly affected, which lines up with the clinical observation that tongue-tie is diagnosed more often in male infants.
A second gene, LGR5, located on chromosome 12, has also been linked to the condition. And researchers have found an association between tongue-tie and mutations in the MTHFR gene, which plays a role in how the body processes folate. The MTHFR connection is still being studied, but it suggests that the metabolic environment during fetal development may influence whether that frenulum tissue properly breaks down.
If you or your partner had a tongue-tie, or if an older child was diagnosed with one, a subsequent baby has a meaningfully higher chance of having one too. The inheritance pattern doesn’t follow a simple dominant or recessive model in most families, which is why it can seem to skip generations or appear unpredictably.
Types of Tongue-Tie
Not all tongue-ties look the same. The Coryllos classification system divides them into four types based on where the frenulum attaches and how it feels:
- Type I: A thin, elastic frenulum anchors the very tip of the tongue to the ridge behind the lower teeth. This is the most obvious type, sometimes giving the tongue a heart-shaped appearance when the baby tries to lift it.
- Type II: The frenulum is still thin and elastic but attaches 2 to 4 millimeters behind the tongue tip, connecting to the floor of the mouth near the lower gum ridge.
- Type III: A thicker, stiffer frenulum anchors the middle of the tongue’s underside to the floor of the mouth. This restricts the tongue’s ability to lift and extend.
- Type IV: Often called a posterior tongue-tie, this type may not be visible at all. The tight fibers sit beneath the mucous membrane and can only be felt by pressing a finger along the floor of the mouth. The surface may look shiny or feel taut.
Types I and II are sometimes grouped as “anterior” tongue-ties and are easier to spot during a routine newborn exam. Types III and IV are “posterior” ties that are harder to identify and more controversial in terms of diagnosis and treatment decisions.
Why Diagnosis Rates Have Climbed
Tongue-tie diagnoses have risen sharply over the past two decades, and the increase isn’t fully explained by better detection. Several factors are at play. Breastfeeding rates have gone up, which means more parents and providers are paying attention to latch difficulties that might have been bypassed with a bottle in earlier generations. At the same time, awareness of posterior tongue-ties (Types III and IV) has expanded the diagnostic net to include ties that would have gone unnoticed before.
The AAP released a clinical report on infant tongue-tie in July 2024, acknowledging both the rise in diagnoses and the lack of well-designed randomized controlled studies on the topic. The report noted that complications from frenulum release procedures do occur, including feeding refusal after the procedure, and called for more careful evaluation before jumping to surgical intervention. The gap between how often tongue-tie is diagnosed and how well we understand its treatment remains one of the more contentious issues in newborn care.
Risk Factors That Increase the Odds
Beyond genetics, a few patterns show up consistently in the research. Male infants are diagnosed with tongue-tie more frequently than female infants, likely because of the X-linked TBX22 gene. If a first-degree relative (parent or sibling) had a tongue-tie, the risk goes up substantially compared to the general population.
There is no strong evidence linking tongue-tie to maternal diet, medication use, or environmental exposures during pregnancy. The condition appears to be primarily genetic and developmental, rooted in how frenulum tissue is programmed to behave during the earliest weeks of embryonic growth. For parents wondering whether they somehow caused it, the short answer is no. The frenulum’s fate is largely set by the baby’s own genetic instructions long before any lifestyle factor could play a role.