This mutation is also known as 621+1G>T and 489+1G>T. It is a Class I splicing mutation, indicating it results in a premature termination codon. If a CF carrier has a child with another CF carrier, then the child has a 25% chance of having Cystic Fibrosis.
In SNPedia and the rest of the world (i.e. outside of the company 23andMe), this SNP is known as rs78756941.