BWS has been shown to specifically involve mutations in a defined region on the short arm of chromosome 11 referred to as 11p15.5, that leads to overactivity of the IGF-2 gene (growth factor) and/or no active copy of CDKN1C (inhibitor of cell proliferation gene).BWS can be caused by a range of different genetic defects. Over five distinct errors involving 11p15.5 have been identified in different BWS patients. Some patients have maternal chromosomal rearrangements of 11p15.5. Other patients have paternal uniparental disomy (UPD) of chromosome 11, meaning that the maternal copy of this chromosome is replaced with an extra paternal copy. Many other patients have abnormal DNA methylation in different areas of 11p15.5, meaning that normal epigenetic marks that regulate imprinted genes in this region are altered. A few other patients have a single gene copy located within 11p15, instead of two copies.The absence of a mutation in a child with clinical findings suggestive of BWS should not preclude a diagnosis of BWS. Even after extensive molecular testing, the specific defect causing BWS in an affected individual may remain unknown. BWS remains a clinical, rather than genetic, diagnosis, since physicians cannot identify and test for all the genetic causes of BWS. The clinical definition used for BWS is limited, because no standard diagnostic criteria exist that have been independently verified with patients who have either genetic or epigenetic mutations.
When molecular analyses were completed in 10 children who met a research criterion for BWS, only 7 of the 10 children had genetic or epigenetic mutations.Given that the genetics of BWS are complex, a child with BWS should be under the medical care of a geneticist or an expert in the management of BWS. Genes involved are IGF-2, CDKN1C, H19, and KCNQ1OT1. Association with CDKN1C
CDKN1C is a protein coding gene that encodes a cyclin-dependent kinase inhibitor that acts as a negative regulator of cell proliferation, effectively making CDKN1C a tumor suppressor gene. CDKN1C also works during fetal development, preventing the fetus from becoming too large. It is located on the short arm of the human chromosome 11 in the ICR2 region, along with many other imprinted genes. Since CDKN1C is preferentially maternally expressed, hypomethylation in the ICR2 region of the maternal allele can result in pathologies such as cancer or a defect known as Beckwith-Weidemann Syndrome. Beckwith-Weidemann Syndrome (BWS) may also be brought about by CDKN1C 11p15 epimutations. It may also be a result of deletions of small amounts of DNA that cause chromosomal abnormalities, rendering the gene inactive. This leaves only the paternally expressed IGF2 to promote cell proliferation. The reduction of growth restriction results in the overgrowth of many tissues, leading to the common symptoms of BWS. These symptoms may include macroglossia, organomegaly, periorbital fullness, and hernias.