BWS (Beckwith-Wiedemann syndrome) is a genetic overgrowth condition present from birth that affects roughly 1 in 10,500 to 13,700 newborns. It occurs because of changes in how certain genes on chromosome 11 are activated, leading to excessive fetal growth, an enlarged tongue, abdominal wall defects, and an increased risk of childhood tumors. Most children with BWS do well with proper monitoring, and many of the most noticeable features improve as they grow older.
How BWS Affects the Body
The hallmark features of BWS revolve around overgrowth. Babies are often born large for their gestational age, typically above the 90th percentile in weight, and may continue to grow faster than expected in early childhood. About 90% of children with BWS have macroglossia, an enlarged tongue that can be significant enough to protrude from the mouth. This is often the most immediately visible sign at birth.
Other common features include omphalocele (where abdominal organs push through the belly button area at birth), enlarged internal organs like the liver or kidneys, and hemihyperplasia, where one side of the body grows noticeably larger than the other. Some children also have distinctive ear creases or small pits on the back of the ear, a facial birthmark called a nevus simplex, and low blood sugar in the newborn period caused by excess insulin production.
Not every child has every feature. BWS exists on a spectrum, and some cases are mild enough that they go undiagnosed for months or even years.
What Causes It
BWS stems from disruptions in a cluster of genes on chromosome 11 (region 11p15.5) that control how quickly a fetus grows. Normally, you inherit two copies of every gene, one from each parent, but some genes are “imprinted,” meaning only the copy from one parent is supposed to be active. In BWS, this system goes wrong.
The key player is a gene that produces a powerful fetal growth factor called IGF2. Normally only the father’s copy is active. In the majority of sporadic BWS cases, both copies switch on, a phenomenon called loss of imprinting. The result is too much growth signal. At the same time, a gene called CDKN1C, which normally acts as a brake on cell division and is active from the mother’s copy, may be silenced or mutated. With the accelerator stuck on and the brake released, tissues overgrow.
Mutations in CDKN1C are particularly associated with omphalocele, appearing in about 81% of patients who carry those mutations. Most BWS cases (around 85%) are sporadic, meaning they occur without a family history. A small percentage are inherited, and families with one affected child can pursue genetic counseling to understand recurrence risk.
Connection to Assisted Reproduction
Children conceived through assisted reproductive technologies like IVF have a roughly 4 to 10 times higher frequency of BWS compared to naturally conceived children. This likely happens because the laboratory handling of embryos can disrupt the delicate imprinting process on chromosome 11. The absolute risk remains low, since BWS itself is rare, but the association is well established enough that fertility specialists are aware of it.
How BWS Is Diagnosed
Diagnosis relies on a combination of clinical features and genetic testing. A widely used scoring system assigns 2 points to cardinal features (macroglossia, omphalocele, lateralized overgrowth, bilateral Wilms tumor, excess insulin production, or placental abnormalities) and 1 point to suggestive features (high birth weight, ear pits, transient low blood sugar, enlarged kidneys or liver, umbilical hernia). A score of 4 or higher confirms BWS clinically. A score of 2 or 3 warrants genetic testing.
Molecular testing looks for methylation changes and other abnormalities at the 11p15.5 region. Current techniques detect the underlying genetic cause in about 80 to 85% of patients with classic or atypical BWS. In milder cases involving only isolated lateralized overgrowth, the detection rate drops to around 11%, which means a negative genetic test does not rule the condition out if the clinical picture fits.
Tumor Risk and Surveillance
The most serious concern with BWS is an elevated risk of embryonal tumors during early childhood. Reported tumor risk estimates range from 4% to 21%, depending on the study and the specific genetic subtype. The most common tumors are Wilms tumor (a kidney cancer) and hepatoblastoma (a liver cancer), both of which are highly treatable when caught early.
Because of this risk, children with BWS follow a structured screening schedule. From birth through age 4, they receive abdominal ultrasounds every 3 months, with views of the liver, adrenal glands, and kidneys, along with blood tests measuring a liver tumor marker called AFP at the same interval. From ages 4 through 7, screening narrows to kidney-only ultrasounds every 3 months. After age 7 or 8, the risk of these childhood tumors drops substantially and routine screening typically stops.
The specific genetic subtype influences tumor risk. For example, certain imprinting patterns carry a higher Wilms tumor risk, while others are more associated with hepatoblastoma. Knowing the molecular subtype helps doctors tailor the surveillance plan.
Managing the Enlarged Tongue
Macroglossia is often the feature that requires the most active management. A significantly enlarged tongue can obstruct the airway, interfere with feeding, delay speech development, and push the teeth and jaw out of alignment over time.
Tongue reduction surgery is considered when there is airway obstruction, feeding difficulty requiring tube feeds, moderate to severe obstructive sleep apnea, speech delay, or progressive dental deformities. Most surgical teams prefer to wait until at least 6 months of age, with many recommending the procedure between ages 2 and 3, to allow time for natural improvement and to reduce the risk of complications or tongue regrowth.
In severe cases, surgery happens much earlier. Babies who need breathing support like continuous positive airway pressure or who have significant sleep apnea in the newborn period may benefit from tongue reduction before 12 months. The earliest reported case was performed at just 12 days of age due to severe airway compromise. The current recommendation is to base timing on symptom severity rather than a fixed age cutoff, with input from sleep specialists, feeding therapists, and surgeons.
Other Early Childhood Concerns
Low blood sugar in the newborn period affects a significant number of BWS babies. In some cases it is mild and temporary, resolving within the first few days of life. In others, the excess insulin production is persistent and requires medical treatment to prevent the neurological damage that prolonged low blood sugar can cause. Monitoring blood glucose levels closely in the first days and weeks after birth is a standard part of BWS care.
Omphalocele or large umbilical hernias may need surgical repair. Kidney abnormalities, including structural malformations and a condition where calcium deposits form in the kidneys, are monitored over time and managed as needed. Children with hemihyperplasia, where limbs on one side grow longer or larger, may eventually need orthopedic input if the leg length difference becomes significant enough to affect walking.
What to Expect Long Term
The overgrowth tendency in BWS generally slows and normalizes during childhood. Many of the most dramatic features, like rapid growth and visceromegaly, become less pronounced by school age. Adults with BWS typically reach a normal or near-normal height and body proportion. Cognitive development is usually unaffected unless there were complications like prolonged low blood sugar in infancy or prematurity.
The tumor risk window is largely confined to the first 8 years of life, which means that once a child ages out of the surveillance period without developing a tumor, that particular concern is essentially behind them. Adults with BWS may still have some residual features like subtle facial characteristics, kidney differences, or leg length discrepancy, but most lead fully independent lives. Genetic counseling is useful for adults with BWS who plan to have children, since the inheritance pattern depends on the specific molecular mechanism involved.