<Tr> <Th> Prognosis </Th> <Td> 5--10% survive past a year old </Td> </Tr> <Tr> <Th> Frequency </Th> <Td> 1 per 5,000 births </Td> </Tr> <P> Edwards syndrome, also known as trisomy 18, is a genetic disorder caused by the presence of all, or part of a third copy of chromosome 18 . Many parts of the body are affected . Babies are often born small and have heart defects . Other features include a small head, small jaw, clenched fists with overlapping fingers, and severe intellectual disability . </P> <P> Most cases of Edwards syndrome occur due to problems during the formation of the reproductive cells or during early development . The rate of disease increases with the mother's age . Rarely cases may be inherited from a person's parents . Occasionally not all cells have the extra chromosome, known as mosaic trisomy, and symptoms in these cases may be less severe . Ultrasound can increase suspicion for the condition, which can be confirmed by amniocentesis . </P>

What gene or chromosome is affected by edwards syndrome