A Yemeni mother who fought to obtain a visa waiver to travel to California to see her terminally ill 2-year-old son was finally reunited with her only child just over a week ago.

On Friday night her son, Abdullah, died at the U.C.S.F. Benioff Children’s Hospital in Oakland, where he was being treated for hypomyelination, a genetic degenerative brain condition, a spokesman for the Council on American-Islamic Relations, a Muslim advocacy group known as CAIR, said on Saturday.

“We are heartbroken. We had to say goodbye to our baby, the light of our lives,” Abdullah’s father, Ali Hassan, said in a statement. “We want to thank everyone for your love and support at this difficult time.”

The family’s plight received widespread attention in the news media and drew support from three members of Congress who wrote a letter to the State Department asking for an expedited decision on the visa waiver.