KBG syndrome is a rare genetic condition that affects multiple body systems, most notably causing unusually large upper front teeth, distinctive facial features, short stature, skeletal differences, and mild to moderate intellectual disability. It is caused by mutations in a gene called ANKRD11, and only one altered copy of this gene is enough to cause the condition. The name “KBG” comes from the initials of the first families described with the syndrome in the 1970s.
What Causes KBG Syndrome
KBG syndrome results from a mutation in the ANKRD11 gene. This gene plays a role in how cells regulate other genes during development, so when it doesn’t work properly, the effects show up across many parts of the body.
The condition follows an autosomal dominant inheritance pattern. That means a child only needs to inherit one copy of the faulty gene (from one parent) to develop the syndrome. In some families, a parent carries the mutation and passes it on. In other cases, the mutation appears for the first time in the child, with no family history at all. These spontaneous (de novo) mutations are common in KBG syndrome.
Recognizable Facial and Physical Features
The most distinctive sign of KBG syndrome is macrodontia, or abnormally large teeth, particularly the upper central incisors. This feature appears in roughly 80% of cases and is often what first prompts a clinical evaluation. Beyond the teeth, dental differences can include missing teeth, extra cusps on the teeth, and weakened enamel.
Facial features tend to be recognizable to clinicians familiar with the syndrome, though they can be subtle in some individuals. Common characteristics include a triangular face shape, a wide or prominent nasal bridge with a bulbous tip, widely spaced eyes, thick or bushy eyebrows that may meet in the middle, prominent ears, a long space between the nose and upper lip, and a thin upper lip. These features are present in 60 to 80% of reported individuals.
Short stature is another hallmark. More than half of people with KBG syndrome have height below what’s expected for their age, and delayed bone age (where the skeleton matures more slowly than usual) is a common finding on X-rays. About 75% of individuals have some form of skeletal difference, most frequently involving the spine and ribs. Short fingers and an inward curve of the fifth finger are also frequently noted. Height tends to fall below the 10th percentile in roughly two-thirds of cases.
Cognitive and Behavioral Profile
Developmental delay is present in nearly all people with KBG syndrome. Delayed motor milestones (like sitting and walking) are typical, and speech delays are particularly common and can be pronounced. Most individuals fall in the mild intellectual disability range when tested, though the spectrum is wide. Measured IQ scores in studied groups have ranged from moderate intellectual disability (around 45) all the way to normal intelligence (around 99).
Behavioral differences are a core part of the condition, not just an occasional feature. Hyperactivity, attention difficulties, and traits associated with ADHD are frequently described, to the point that the behavioral profile has been characterized as “ADHD-like.” Autism-related features have also been documented in multiple case studies, though systematic research on this link is still limited. Aggression and other behavioral challenges can occur as well.
Seizures and Epilepsy
Epilepsy affects a significant portion of people with KBG syndrome. In a study of 75 patients, about 35% were diagnosed with epilepsy. Seizures typically begin around age 4, though onset has been documented as early as 12 months and as late as 20 years.
The most common seizure pattern is generalized onset, with tonic-clonic seizures (formerly called grand mal) being the single most frequent type. Many individuals have a combined pattern involving both generalized and focal seizures. There is no single epilepsy syndrome specific to KBG, but overlap has been seen with several recognized childhood epilepsy types. Notably, the presence of epilepsy is associated with poorer developmental outcomes, making early recognition and management important.
Other Health Concerns
KBG syndrome can come with a range of additional medical issues that vary considerably from person to person. Feeding difficulties are common in early childhood. Recurrent middle ear infections and hearing loss occur frequently enough that hearing should be monitored from an early age. Visual problems are also reported at higher-than-expected rates.
Heart differences, including congenital heart defects and widening of the aorta, have been reported more often than in the general population. Gastrointestinal issues, including cyclical vomiting and abdominal migraines, can persist into adulthood. Palatal abnormalities (differences in the roof of the mouth) and early onset of puberty are additional features that clinicians watch for.
How KBG Syndrome Is Diagnosed
Diagnosis is based on a combination of clinical features and genetic testing. There are no formal consensus diagnostic criteria, so clinicians look for the pattern: large upper central incisors, characteristic facial features, short stature, skeletal findings, and developmental delay. The large teeth are often the single most helpful clue, since macrodontia is relatively uncommon in other genetic conditions.
Genetic testing for mutations in ANKRD11 can confirm the diagnosis. This is especially valuable because the facial features can be subtle, particularly in very young children or in mildly affected individuals who might otherwise go undiagnosed.
Living With KBG Syndrome as an Adult
Most published research on KBG syndrome has focused on children, but a 2025 study surveying 91 adults with the condition has started filling in the picture of what life looks like beyond childhood. The findings show that many of the health challenges from childhood, including seizures, psychiatric conditions, sleep problems, dental and skeletal issues, and vision and hearing difficulties, continue to affect quality of life into adulthood.
Some adults with KBG syndrome do achieve meaningful independence. The study found that skills like independent living, grocery shopping, and driving were acquired by some individuals, with the highest rates of skill attainment in the 35-to-44 age group. However, people who continued to experience seizures in adulthood were much less likely to live independently. The researchers noted that the diagnosis alone should not set limits on someone’s future aspirations, since the condition affects people in highly variable ways.
Life expectancy is not well characterized in existing research, but the condition is not described as life-limiting in itself. The key to long-term wellbeing appears to be ongoing monitoring and management of the various comorbidities, particularly heart health, seizures, and mental health, that can accumulate over time.