Test ID: BWS
Beckwith-Wiedemann Syndrome (BWS) Methylation Analysis, Blood

Confirming a clinical diagnosis of Beckwith-Wiedemann syndrome (BWS)

Assessing prenatal cases if there is a high suspicion of risk for BWS based on ultrasound findings

Germline and prenatal testing are available on blood and amniocyte specimens, respectively. Prenatal testing for Beckwith-Wiedemann syndrome cannot be performed on chorionic villus specimens.

Beckwith-Wiedemann syndrome (BWS) is a disorder characterized by prenatal and/or postnatal overgrowth, neonatal hypoglycemia, congenital malformations, and an increased risk for embryonal tumors. Physical findings are variable and can include abdominal wall defects, macroglossia, and hemihyperplasia. The predisposition for tumor development is associated with specific tumor types such as adrenal carcinoma, nephroblastoma (Wilms tumor), hepatoblastoma, and rhabdomyosarcoma. In infancy, BWS has a mortality rate of approximately 20%.

Current data suggest that the etiology of BWS is due to dysregulation of imprinted genes in the 11p15 region of chromosome 11. Imprinting describes a difference in gene expression based on parent of origin. The majority of autosomal genes exhibit biallelic (maternal and paternal) expression, whereas imprinted genes normally express only 1 gene copy (either from the maternal or paternal allele). Imprinted genes are usually regulated by methylation, which prevents the gene from being expressed. Loss of expression or biallelic expression of an imprinted gene can lead to disease because of dosage imbalance. Some of the imprinted genes located in the region of 11p15 include H19 (maternally expressed), LIT1 (official symbol KCNQ1OT1; paternally expressed), IGF2 (paternally expressed), and CDKN1C (aliases p57 and KIP2; maternally expressed).

Approximately 85% of BWS cases appear to be sporadic, while 15% of cases are associated with an autosomal dominant inheritance pattern. When a family history is present, the etiology is often due to inherited point mutations in CDKN1C or an unknown cause. The etiology of sporadic cases includes:

-Hypomethylation of LIT1: approximately 50% to 60%

-Paternal uniparental disomy of chromosome 11: approximately 10% to 20%

-Hypermethylation of H19: approximately 2% to 7%

-Unknown: approximately 10% to 20%

-Point mutation in CDKN1C: approximately 5% to 10%

-Cytogenetic abnormality: approximately 1% to 2%

-Differentially methylated region 1 (DMR1) or DMR2 microdeletion: rare

The clinical presentation of BWS is dependent on which gene in the 11p15 region is involved. The risk for cancer has been shown to be significantly higher in patients with abnormal methylation of H19 versus LIT1. In patients with abnormal methylation of LIT1, abdominal wall defects and overgrowth are seen at a higher frequency.

Methylation abnormalities of LIT1 and H19 can be detected by methylation-sensitive multiple ligation-dependent probe amplification (MLPA) assay. While testing can determine methylation status, it does not identify the mechanism responsible for the methylation defect (such as paternal uniparental disomy or cytogenetic abnormalities). Normally, LIT1 is expressed from the paternal allele only, while H19 is expressed only from the maternal allele. Hypomethylation of the maternal copy of LIT1 is hypothesized to silence the expression of a number of maternally expressed genes, including CDKN1C. Hypermethylation of the maternal copy of H19 is hypothesized to silence the expression of H19 while also resulting in over-expression of IGF2. Absence of CDKN1C and H19 expression, in addition to over expression of IGF2, is postulated to contribute to the clinical phenotype of BWS.

An interpretive report will be provided.

An interpretive report will be provided.

In addition to disease-related probes, the multiple ligation-dependent probe amplification technique utilizes probes localized to other chromosomal regions as internal controls. In certain circumstances, these control probes may detect other diseases or conditions for which this test was not specifically intended. Results of the control probes are not normally reported. However, in cases where clinically relevant information is identified, the ordering physician will be informed of the result and provided with recommendations for any appropriate follow-up testing.

Rare polymorphisms exist that could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, additional testing should be considered.

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in our interpretation of results may occur if information given is inaccurate or incomplete.

Methylation status cannot be assessed on chorionic villus specimens.

A previous bone marrow transplant from an allogenic donor will interfere with testing. Call Mayo Medical Laboratories for instructions for testing patients who have received a bone marrow transplant.

This assay does not detect mutations in the CDKN1C (p57 [KIP2]) gene or balanced cytogenetic abnormalities such as translocations or inversions.

Normal methylation index was derived by studying 150 normal individuals. For 65 patients referred for Beckwith-Wiedemann syndrome testing, results of this multiple ligation-dependent probe amplification (MLPA) assay were compared to a Southern blot method. Results were concordant for 64 of 65 specimens. In 1 specimen, a deletion was identified by MLPA that was not detected by the Southern blot method.

1. DeBaun MR, Niemitz EL, McNeil DE, et al: Epigenetic alterations of H19 and LIT1 distinguish patients with Beckwith-Wiedemann Syndrome with cancer and birth defects. HumGenet 2002:70:604-611            

2. Choufani S, Shuman C & Weksberg R: Beckwith-Wiedemann Syndrome. Am J of Med Genet 2010:154C:343-354

3. Priolo M, Sparago A, Mammi C, et al: MS-MLPA is a specific and sensitive technique for detecting all chromosome 11p15.5 imprinting defects of BWS and SRS in a single-tube experiment. Euro J of Hum Genet 2008:16:565-571

4. Lennerz JK, Timmerman RJ, Grange DK, et al: Addition of H19 ‘Loss of Methylation Testing’ for Beckwith-Wiedemann Syndrome (BWS) Increases the Diagnostic Yield. J of Molecular Diagnostics 2010:12(5):576-588

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