On a chilly afternoon in early spring, Mayumi Mitogawa, 52, and her 14-year-old son, Yutaka, sat together on a bench, getting ready to have their picture taken. He jokingly made a face and tried to push her out of the way, showing a hint of the shyness common to teens about being seen with their mom.

"He just loves to make people laugh," Mitogawa said, smiling affectionately at her son — who was born with trisomy 21, which causes Down syndrome — as he fooled around mimicking the motions of famous Japanese comedians. "I know that some people refer to children with Down syndrome as angels, but I don't see my son like that. He is just human."

Down syndrome is caused by an extra copy of chromosome 21. Symptoms include specific physical characteristics and intellectual disability, and often potential complications of the heart and other internal organs. It is estimated that 1 out of 1,000 babies are born with trisomy 21, and various medical studies show that the older the mother is, the higher the risk.