» What causes Cornelia de Lange Syndrome


Mosaicism, means there are different groups of cells with different genetic make-up in a person. This means that some cells in the person will have the mutation and others will not. Mosaicism has been found to occur frequently in CdLS (23). Approximately 15-20% of individuals with classic features of CdLS have mosaic changes in NIPBL; and although it is rare, individuals with CdLS can also have mosaic changes in SMC3, RAD21 or SMC1A. These mosaic changes cannot be found using genetic testing that examines an individual’s DNA from their white blood cells (23,24,46).

In some circumstances, if an individual is found to be mosaic for a mutation, it is thought that there could be a variation in the severity of the clinical findings. However, there is no evidence that this occurs in CdLS. It is suggested that there may be a selection against these gene changes occurring in blood cells (41, 23, 46), meaning they may not be identified using blood tests. Genetic testing can evaluate DNA for mosaicism by examining fibroblasts (connective tissue cells), buccal cells (cheek cells) or bladder epithelial cells (cells in urine) instead (R5) (23,24).

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