At only 8 years old, Jonathan Martinez was already a survivor.

He had endured heart surgery and many other challenges presented by Williams syndrome, a rare neurodevelopmental disorder marked by cardiovascular disease, developmental delays and learning disabilities, as well as impressive creative talents.

On Monday, however, the little boy with the bright smile came face to face with an obstacle he couldn’t overcome: a gunman who entered his special education classroom at North Park Elementary in San Bernardino, Calif., and started shooting. Jonathan was fatally struck as he stood near his teacher, Karen Elaine Smith, who was shot dead by Cedric Anderson, her estranged husband.

“By all accounts, Jonathan Martinez was a happy and friendly child,” San Bernardino City Unified Superintendent Dale Marsden said at a news conference Tuesday.

Though special-education students are often saddled with stereotypes, Jonathan was born with a genetic disorder that defies preconception. Though Williams syndrome can lead to health problems and cognitive challenges, people with the disorder are also known for being extroverted, passionate and creatively inclined.

“Unlike disorders that can make connecting with your child difficult, children with Williams syndrome tend to be social, friendly and endearing,” Marsden said, reading from a description on the Williams Syndrome Association website.

“Parents often say the joy and perspective a child with this syndrome brings into their lives had been unimaginable,” he added.

Marsden added that the Martinez family wants to use their tragic loss to raise awareness about Williams syndrome, which affects up to 30,000 people in the United States, according to the Williams Syndrome Association.

A GoFundMe page that refers to Jonathan as “our family angel” and seeks to raise money for his funeral has raised more than $82,000 in less than a day.

The syndrome is genetically based, affecting males and females, researchers say. The disorder is caused by the deletion of about 26 genes on a copy of an individual’s No. 7 chromosome, according to the Williams Syndrome Association. Babies with Williams syndrome often face grave cardiovascular problems, while children face challenges understanding abstract reasoning and numbers, researchers say. Challenges can include kidney problems, hypersensitive hearing and poor motor skills, according to the association.

In a paper exploring the genetic origins of the syndrome — “The Neurocognitive Profile of Williams Syndrome: A Complex Pattern of Strengths and Weaknesses” — researchers from the Salk Institute for Biological Studies and the University of California at San Diego describe a little girl named Crystal to highlight the challenges the syndrome presents.

At 14, the researchers write, Crystal is “enthusiastic” and “ambitious.” She enjoys creating original stories and telling them on the spot and says things like, “You’re looking at a professional book writer.”

She is also a music lover who has composed lyrics and notes for a song.

“Considering her ease with language, her creative ideas, and her unshaking enthusiasm, her ambition to become a writer may seem plausible — however, Crystal has an IQ of 49,” the researchers write. “She fails all Piagetian seriation and conservation tasks, milestones normally attained by age 8. She has reading, writing, and math skills comparable to those of a first-grader, demonstrates visuo-spatial abilities of a 5- year-old, and cannot be left alone without a babysitter.”

In adulthood, people with Williams syndrome can often hold jobs or work as volunteers but benefit from supportive housing, according to the Williams Syndrome Association. Among their biggest challenges in adulthood is finding people to bond with.

“As people with Williams syndrome mature — beyond the structure of school and family activities — they often experience intense isolation which can lead to depression,” the association notes. “They are extremely sociable and experience the normal need to connect with others; however people with Williams syndrome often don’t process nuanced social cues and this makes it difficult to form lasting relationships.”