The first grader who died earlier this week after collapsing at a South Philadelphia elementary school had a congenital heart defect that caused his death, the medical examiner's office said Friday.

The child, Sebastian Gerena, 7, had an "anomalous origin of the left coronary artery," said James Garrow, a spokesman for the Philadelphia Health Department. The condition was discovered during an autopsy Thursday.

Researchers have found that the condition can lead to sudden death. Typically, less blood reaches the heart because of the irregularity, and the blood that does reach the heart lacks sufficient oxygen.

The boy attended Jackson Elementary School in South Philadelphia, where he experienced a medical emergency Wednesday afternoon and appeared to stop breathing.

School staff administered CPR and called 911. The child was taken to Children's Hospital of Philadelphia, where doctors pronounced him dead.

A nurse works at the school only on Thursdays and every other Friday as a result of budget constraints. A retired nurse who happened to be volunteering at the school on Wednesday was among those who performed CPR on the child before emergency personnel arrived.

The boy's death seized the attention of the school community and education advocates who demonstrated Thursday seeking more funding for the Philadelphia School District.

Students, educators and activists marched in the rain Thursday from City Hall to Gov. Corbett's office, demanding additional money from the city and state for the district's cash-strapped schools. They called for the restoration of counselors and nurses.

On Friday, Gov. Corbett said he was "deeply troubled" by teachers' union officials using "the recent tragedy at Andrew Jackson Elementary School as an opportunity to make a political statement and to further your self-serving agenda."

Writing in response to a letter from city, state, and national union leaders, Corbett said: "I offer my sincere condolences to the family of the child, and I want to commend the staff at Jackson Elementary for their prompt response. As a parent and grandparent, I can only imagine how heartbreaking this loss is for the child's family, classmates, teachers and friends."

In a letter released by the governor's staff, Corbett wrote that the Philadelphia School District was "following regulations, like every other school district in Pennsylvania, for staffing their schools with school nurses.

"In Philadelphia's case, as you point out in your letter, that nursing decision was made five years ago, prior to me taking office, by the school district administration," Corbett wrote. "Faculty and support staff across the commonwealth are trained in first aid/CPR to intervene in case of an emergency - as was done by the staff at Andrew Jackson Elementary School this week."

Jerry Jordan, president of the Philadelphia Federation of Teachers, said in a statement Friday afternoon: "Our letter to the governor says it all: We need more nurses, counselors and other services for children in our schools. We want Corbett and his School Reform Commission to take ownership for denying these programs to Philadelphia's schoolchildren, and take responsibility for restoring them.

"The city is grieving the loss of a young child in school for a second time this school year - we need public education funding that will help prevent tragedies like this from occurring again."

A sixth grader died after suffering an asthma attack in October.