About wiedmann-beckwith syndrome
What is wiedmann-beckwith syndrome?
Beckwith-Wiedemann syndrome (BWS) is a rare genetic overgrowth disorder. It is characterized by a wide spectrum of symptoms and physical findings that vary in range and severity from case to case. However, in many individuals, associated features include above-average birth and weight and increased growth after birth (postnatally), an usually large tongue (macroglossia), enlargement of certain internal organs (visceromegaly), and protrusion of a portion of the intestines and abdominal organs through a tear in the wall of the stomach or bellybutton (abdominal wall defects). BWS may also be associated with low blood sugar levels within the first few days or the first month of life (neonatal hypoglycemia), advanced bone age, particularly up to age four; distinctive grooves in the ear lobes and other facial abnormalities, abnormal enlargement of one side or structure of the body (hemihyperplasia) may occur, resulting in unequal (asymmetric) growth, and an increased risk of developing certain childhood cancers.
In approximately 85 percent of cases, BWS results from genetic changes that appear to occur randomly (sporadically). Approximately 10-15 percent of cases of this syndrome run in families and show autosomal dominant inheritance. Researchers have determined that BWS results from various abnormalities affecting the proper expression or structure of certain genes within a specific region of chromosome 11.
What are the symptoms for wiedmann-beckwith syndrome?
The phenotypic features of BWS vary greatly from person to person, which can make clinical diagnosis based on physical exam findings and molecular diagnosis based on genetic testing challenging. Sometimes, the clinical and molecular diagnoses do not match because clinically the patients may not have many salient physical features of BWS even if they have changes in the BWS critical region based on genetic testing. Some individuals may appear mildly affected while others appear more significantly affected. Affected individuals may not have all of the symptoms listed. The range of clinical features due to changes on chromosome 11p15.5 has been redefined as the Beckwith-Wiedemann spectrum.
Diagnosis of BWS can be challenging because patients are often mosaic as the genetic abnormalities characteristic of BWS may occur in some cells or parts of the body but not others). For this reason, it may be helpful to perform genetic testing on multiple tissues (such as skin biopsies or removed tumors or pancreas tissue).
Some infants with BWS are born prematurely, but still have an excessive birth weight (large for gestational age). Over half of infants with BWS are above the 97th percentile in weight for gestational age. Overgrowth can continue throughout childhood (macrosomia). Abnormal enlargement of one side or structure of the body (lateralized overgrowth) may occur, resulting in asymmetric growth. Lateralized overgrowth or isolated lateralized overgrowth (ILO) is a new term used to describe what was previously termed hemihypertrophy or hemihyperplasia. ILO is defined as asymmetric overgrowth of the body. ILO is not limited to one side of the body and it does not specify what part or tissue is displaying overgrowth. For example, a patient may have a larger left arm and a larger right leg.
Abdominal wall defects can include an omphalocele (also known as exomphalos), in which part of an infant’s intestines and abdominal organs are outside of the body because of an opening in the belly button. The intestines and other organs are covered by a thin membrane. Less severe abdominal defects can include protrusion of part of the intestines through an abnormal opening in the muscular wall of the abdomen near the umbilical cord (umbilical hernia), or Weakness and separation of the left and right muscles of the abdominal wall (diastasis recti). Additionally, the internal organs of affected individuals can become abnormally enlarged (organomegaly). Any or all of the following organs may be affected: liver, spleen, pancreas, kidneys, or adrenal glands.
Some newborns with BWS may have Low blood sugar (neonatal hypoglycemia or hyperinsulinism) due to overgrowth and excessive secretion of the hormone insulin by the pancreas. Insulin helps regulate blood glucose levels by promoting the movement of glucose into cells. Most infants with neonatal hypoglycemia associated with BWS have mild and transient symptoms. However, without proper detection and appropriate treatment, neurological complications may result. Congenital hyperinsulinism is the most common cause for persistent and severe low blood sugar.
Patients with BWS may have an enlarged tongue (macroglossia), which can cause difficulties in speaking, feeding, and breathing. In addition to macroglossia, BWS may be characterized by other abnormalities of the skull and facial (craniofacial) region. Such features may include distinctive slit-like grooves or creases in the ear lobes and dimples on the back of the ears (ear creases or pits), Prominent eyes with relative underdevelopment of the bony cavity of the eyes (intraorbital hypoplasia), and/or a prominent back region of the skull (occiput). Some infants may have flat, pale red or reddish purple facial marks at birth, most commonly on the eyelids and forehead, which consist of abnormal clusters of small blood vessels (facial nevus simplex). Such marks typically become less apparent during the first year of life. In patients with lateralized overgrowth, one side of the face may appear larger than the other. Due to the mosaic nature of BWS, some patients have eyes with multiple colors. Additionally, in some affected patients, there may be improper contact of the teeth of the upper and lower jaws (malocclusion) and abnormal protrusion of the lower jaw (mandibular prognathism), features that may occur secondary to macroglossia.
A variety of kidney (renal) abnormalities can occur in individuals with BWS, including abnormally large kidneys (nephromegaly), improper development of the innermost tissues of the kidney (renal medullary dysplasia), and the formation of calcium deposits in the kidney (nephrocalcinosis), which could potentially impair kidney function. Additional abnormalities include duplication of the series of tubes and ducts through which the kidneys reabsorb water and sodium (duplicated collecting system), widening of some of the small tubes and collecting ducts (medullary sponge kidney), and the presence of small pouches (diverticula) on the kidneys. Kidney stones have been reported to occur in adolescents and adults with BWS.
Patients with BWS may have an increased risk of developing certain childhood cancers. Embryonal cancers occur in approximately 8% of patients with BWS. The most common types of tumors are Wilms tumor (a kidney tumor), hepatoblastoma (a liver tumor), neuroblastoma (a nerve cell tumor), rhabdomyosarcoma (a soft tissue tumor), and adrenal carcinoma (an adrenal gland tumor). The overall tumor risk is highest during the first two years of life.
Many clinical features of BWS become less evident with increasing age and many adults experience normal growth and appearance. Neurological (brain) development appears to be unaffected in BWS, unless associated with prolonged, untreated neonatal hypoglycemia, extreme prematurity, or a chromosomal duplication. Adult patients may present with medical issues related to these clinical features or have required surgical intervention in early childhood. Most features in adults with BWS, such as renal issues and back pain, are consequences of pediatric issues. However, more research is needed to determine the relationship between features of adults with BWS and pediatric symptoms.
What are the causes for wiedmann-beckwith syndrome?
Genetics is the study of genes whereas epigenetics is the study of how those genes are turned on or off (gene expression). BWS results from various abnormalities affecting the proper expression of genes that control growth within a specific region of chromosome 11(11p15.5). This region is referred to as the BWS critical region.
Approximately 80% of people with BWS have no family history of this syndrome. For these people, BWS is usually caused by epigenetic changes that appear to occur randomly (sporadically). More rarely, BWS is caused by genetic changes that are passed down from a parent (inherited). Approximately 5-10% of patients have BWS due to a family history of the syndrome. About 14% of patients with BWS have an unknown cause for diagnosis.
Everyone has two copies of every gene, one received from the father and one received from the mother. In most people, both genes are “turned on” or active. However, some genes are “turned off” or preferentially silenced based upon which parent that gene came from (a process known as genomic imprinting). Genomic imprinting is controlled by marks on the DNA called methylation. Proper genomic imprinting is necessary for normal development and defective imprinting on chromosome 11 can lead to BWS. Several genes that control growth on chromosome 11 are imprinted, which means that the gene is only active from the mother’s chromosome or the father’s chromosome but not both.
Imprinted genes tend to be clustered or grouped together. Chromosome 11p15.5 has two imprinting cluster regions known as imprinting centers 1 and 2 (IC1 and IC2). Several specific imprinted genes are located in these regions. The improper imprinting of these two regions leads to the improper expression of the genes located within the regions, playing a role in the development of BWS. These genes include H19 (a gene that signals not to grow), IGF2 (insulin-like growth factor II), KCNQ10T1 (LIT1), and CDKN1C (p57[KIP2])(a gene that signals not to grow).
H19 is a long noncoding RNA thought to play a role in inhibiting growth. IGF2 is a growth factor. KCNQ10T1 is a noncoding RNA and CDKN1C is a cell cycle regulator and tumor suppressor. Researchers believe that the paternally-expressed genes promote growth and that the maternally-expressed genes act as tumor suppressor genes or inhibit growth. Normally, H19 and CDKN1C are expressed from the maternal chromosome and IGF2 and KCNQ1OT1 are expressed from the paternal chromosome. Improper methylation in the BWS critical region can lead to an imbalance of the “grow” and “don’t grow” signals, leading to overgrowth.
Gain of methylation (hypermethylation) at imprinting center 1 (IC1 GOM) occurs in about 5% of patients with BWS. This leads to decreased H19 expression and increased IGF2 expression.
Imprinting center 2 (IC2) is associated with KvDMR, a chemical switch found on the KCNQ1 gene. Loss of methylation (hypomethylation) at KvDMR of imprinting center 2 (IC2 LOM) occurs in about 50% of people with BWS. This leads to increased KCNQ10T1 (long QT intronic transcript 1 [LIT1]) expression and decreased CDKN1C expression.
Imprinting errors may also be caused by a chromosomal abnormality known as uniparental disomy (UPD). UPD occurs when a person receives both copies of a chromosome (or part of a chromosome) from one parent instead of receiving one copy from each parent. Approximately 20% of people with BWS have UPD. In BWS, both copies of chromosome 11 are received from the father (paternal uniparental disomy (pUPD)). As a result, there are too many active paternally-expressed genes (IGF2) in this region and not enough maternally-expressed genes (H19, CDKN1C). Uniparental paternal disomy occurs after fertilization (post-zygotic), and therefore the risk of recurrence is extremely low.
Mosaic genome-wide paternal uniparental isodisomy (GWpUPD) occurs in about 10% of BWS due to pUPD (approximately 2% of all patients with BWS). In the case of GWpUPD, every chromosome is inherited from the father in the cells that carries the abnormality, instead of just chromosome 11 as in pUPD. GWpUPD is associated with a greater tumor risk. The severity of GWpUPD varies according the number of cells affected and where the affected cells are located within the patient.
Abnormal changes (mutations) of the CDKN1C gene have been detected in some individuals with BWS. The loss of proper expression or “underexpression” of the gene is thought to play an important role in causing the disorder. Approximately 5% of people with BWS are found to have mutations of the CDKN1C gene. The mutation is inherited as an autosomal dominant trait, which means that only one copy of the mutated gene is needed to pass down the disorder. However, CDKN1C is normally only maternally expressed, and therefore, the offspring will only be affected (i.e. have BWS) if the mutation is passed from mother to offspring. Approximately 40% of individuals with a family history of BWS have mutations of the CDKN1C gene. Mutations in CDKN1C can also occur randomly without the mother carrying the change (de novo mutation). Patients with BWS due to CDKN1C changes have a 50% risk of passing the mutation to their children.
Research has shown that small deletions (microdeletions) affecting imprinting center 1 (IC1) of chromosome 11p15.5 may be the cause of familial BWS in some people. Approximately 1-2% of patients with BWS have deletions involving 11p15.5. Microdeletions of the KCNQ10T1 (LIT1) gene have also been identified in some people with BWS. These microdeletions appear to cause BWS when inherited maternally; when inherited paternally, the disorder does not develop. Small duplications (microduplications), affecting imprinting center 1 (IC1) of chromosome 11p15.5 inherited from the father can also cause BWS. These microduplications can also occur randomly (de novo).
Approximately 2-4% of cases of BWS are due to various chromosomal abnormalities involving the 11p15.5 chromosomal region. This includes chromosomal inversions or rearrangements (translocations) or the presence of extra chromosomal material (duplications).
Phenotype genotype correlation: Researchers are investigating if specific causes of BWS are associated with specific symptoms (genotype-phenotype correlation). Research indicates that omphalocele and macroglossia are more common in individuals with defects of IC2 or a mutation of the CDKN1C gene. Patients with pUPD are at a greater risk for lateralized overgrowth and hyperinsulinism. Individuals with defects of IC1 or pUPD appear to be at a greater risk of developing an associated tumor such as Wilms tumor. Patients with pUPD are also have a greater risk of developing a liver tumor (hepatoblastoma). The different molecular types of BWS each carry a different tumor risk. More research is necessary to determine how the specific causes of BWS correlate with the various symptoms of the disorder.
What are the treatments for wiedmann-beckwith syndrome?
The treatment of BWS is directed toward the specific symptoms that are apparent in each individual. Treatment may require the coordinated efforts of a team of specialists. Geneticists, pediatricians, plastic surgeons, endocrinologists, nephrologists (kidney specialists), orthodontists (dental specialists), pulmonologists (lung specialists), speech pathologists, pediatric oncologists, and other healthcare professionals may need to systematically and comprehensively plan an affected child’s treatment.
In newborns with BWS, regular monitoring of blood glucose levels should be performed to ensure prompt detection and treatment of hypoglycemia. Although neonatal hypoglycemia is usually mild and temporary, its early detection and treatment is essential in preventing associated neurologic complications. Treatment measures may include the administration of intravenous glucose, frequent feedings, certain medications (e.g., diazoxide or octreotide), and/or surgical intervention in some cases.
In many infants with umbilical hernia, the defect may spontaneously disappear by the age of approximately one year. Surgery is usually not required unless an umbilical hernia becomes progressively larger, does not spontaneously resolve (e.g., by about three or four years of age), and/or is associated with certain complications. However, in newborns with an omphalocele, surgical repair of the defect is typically required shortly after birth.
Similar to other features associated with BWS, macroglossia can vary in severity. Patients with macroglossia are at an increased risk for obstructive sleep apnea, feeding difficulties, speech difficulties, and potential jaw development issues. Patients with macroglossia require the support of a multidisciplinary team. They should undergo feeding evaluation and sleep studies in addition to consultations with plastic surgeons and pulmonologists if needed. Feeding difficulties caused by macroglossia may require the support of feeding specialists or dieticians. Treatment may include the use of specialized nipples or the temporary insertion of a nasogastric tube. Speech difficulties may require the support of speech therapy. A pulmonologist can evaluate the degree to which macroglossia affects a patient’s breathing and sleeping. A polysomnography (sleep study) may be used to assess for obstructive sleep apnea, airway obstruction, airway resistance, severe desaturation, sleep disordered breathing, and snoring. Continuous positive airway pressure (CPAP) is a method used to support children with obstructive sleep apnea. Some patients may undergo tongue reduction surgery with the goal of improving breathing, feeding, and jaw or dental malformations due to macroglossia. Patients with macroglossia should be followed closely by a multidisciplinary team.
Regular orthopedic evaluation is recommended for patients with lateralized overgrowth. Some patients with significant lateralized overgrowth of the limbs may require shoe lifts and in some cases, surgical correction may be needed.
In addition, infants and patients with BWS should undergo regular abdominal and renal ultrasounds, and measurement of serum alpha-fetoprotein levels as recommended enabling early detection and treatment of certain malignancies that may occur in association with BWS (e.g., Wilms tumor, hepatoblastoma).
Alpha-fetoprotein (AFP) is a protein produced by the liver. AFP levels typically decline during infancy; however, AFP may be abnormally elevated in blood if certain tumors are present (hepatoblastoma). The trend in AFP levels over time should be followed in patients with BWS and normal AFP values for children with BWS are available to aid in interpretation of results. There have been recent discussions regarding the utility of AFP screening in young children. While some suggest that the invasiveness of a regular blood draw may be stressful for many families, AFP has proven to be a useful early indicator for hepatoblastoma.
According to the United States-based guidelines, screening is recommended for all patients with a clinical or molecular diagnosis of BWS by AFP analysis and a full abdominal ultrasound every three months until the 4th birthday (to screen for hepatoblastoma and Wilms tumor) followed by renal ultrasounds every 3 months until 7th birthday (to screen for Wilms tumor). Additional screening by urine analysis for neuroblastoma is recommended for patients with CDKN1C mutations. Also, screening for patients with BWS due to GWpUPD may extend beyond the 7th birthday.
If a tumor develops in association with BWS, the appropriate treatment measures vary depending on the specific tumor present, the stage and/or extent of disease, and/or other factors. Treatment methods may include surgery (for example, nephron-sparing kidney resection in the case of a Wilms tumor), use of certain anticancer drugs (chemotherapy), radiation therapy, and/or other measures. (For more information on Wilms tumor, choose “Wilms” as your search term in the Rare Disease Database.)
Patients with cardiac, gastrointestinal, and renal abnormalities may require certain medications, surgery, or other medical interventions. These patients should be referred to appropriate specialists. Genetic counseling may be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.
Late-onset complications with BWS may require continued follow-up in adulthood. More research is needed to understand the features and associated treatments for adults with BWS.
What are the risk factors for wiedmann-beckwith syndrome?
BWS affects males and females in equal numbers. It is estimated to occur in 1 in 10,340 individuals in the general population. Because people who are mildly affected may go undiagnosed, it is difficult to determine the true frequency of BWS in the general population.
There is no specific increased risk for BWS within specific race/ethnicity populations although the clinical presentations may vary between groups.
Research suggests that patients conceived with assistive reproductive technology (ART), such as in vitro fertilization (IVF) and/or intracytoplasmic sperm injection (ICSI), may be at a greater risk of developing disorders resulting from genomic imprinting (such as BWS) than the general population. A recent study revealed a tenfold increased risk for BWS in patients conceived via ART, with a prevalence of one in 1,126 patients. The majority of patients with BWS who are conceived through ART have BWS due to IC2 LOM. More research is necessary to determine the exact relationship between such technologies and the development of BWS.
Studies have also shown that the frequency of twin pregnancies is more common in the BWS population than in the general population. However, twins with BWS tend to present with varying levels of severity (discordance) making it challenging for physicians to diagnose and manage twins with BWS.