FALMOUTH — Tess Bigelow has a gene mutation so rare there’s not even a name for it.

The developmentlly delayed 8-year-old, who attends Falmouth Elementary School, functions more on the level of a toddler; she learned to walk last year and does not speak.

But every day she’s becoming more and more independent, according to her mother, Dr. Kate McCrann, and that’s in no small part due to the support the family has received.

Now Bigelow’s young cousins, Patrick, 8, and Max McCrann, 5, have set up a neighborhood lemonade stand in the hope of raising enough money to help cover some of Tess’ many expenses.

While serving $1 glasses of lemonade on a summer weekend may not make much of a dent in the more than $100,000 needed to perform a phenotype study on Tess, the boys are well on their way toward their target goal of $1,000.

If they can raise that amount by the end of the summer, Patrick McCrann said, they can help the Bigelows purchase a special piece of equipment that would help Tess function better day-to-day.

On June 9, many people stopped by the McCranns’ stand at the corner of Johnson and Raymond roads in Falmouth Foreside, to offer their support and encouragement.

Kate McCrann said her daughter has received “tons of testing” over the years and had her genome mapped in an effort to discover what is causing her neurodevelopmental disorder.

What the Bigelow family learned is that Tess has a mutation in the USP7 gene, which has caused developmental delay and also led to hip dysplasia and visual impairment.

Although the Bigelow family has so far only been able to discover 30 or so other kids like Tess around the world, the common denominator for those with the USP7 mutation seems to be severe developmental delay, brain and spinal cord abnormalities, and speech impairment. All of the children are also on the autism spectrum.

McCrann said her daughter receives regular physical, occupational, speech and vision therapy, and can make herself understood by using a special assistive communications device.

McCrann said she and her husband, Bo Bigelow, “are blessed” to live in Falmouth “where everyone is nothing but supportive.”

Included in those who accept Tess for who she is, McCrann said, is Tess’ older brother, Dana Bigelow, a sixth-grader at Falmouth Middle School. “He’s a fantastic, unreal older brother, who takes on a lot of responsibility,” she said.

As a doctor who practices gastroenterology, “I knew nothing about pediatrics or child development,” McCrann said, “but as a mother I knew something was different about Tess almost from the moment she was born.”

After finally learning what caused their daughter’s condition, Bigelow and McCrann, who practices at Mercy Hospital, created the Foundation for USP7 Related Diseases

The foundation is working to provide “a future of possibilities” for those who are diagnosed with the disorder, according to the organization’s website, with the ultimate goal of curing the disease.

Meanwhile, the lemonade stand being run by Tess’ cousins has caught the attention of the social media platform Nextdoor, which has named it one of the 10 best in the country.

Annie Barco, communications manager for Nextdoor, said the criteria for choosing the top lemonade stands include “the passion and inspiration for the charity they are supporting and community involvement.”

She said Nextdoor has also pledged to match the amount raised by the McCrann brothers, up to $500.

In recognizing neighborhood lemonade stands, Barco said the hope is for “these kids to realize they have the power to enact change … and that something as simple as a lemonade stand can positively impact someone else’s life in a big way.”

In running their lemonade stand, the McCranns have the help of their neighbors Peter and Jonathan Kearns, who are 10 and 8.

Jonathan Kearns said he and his brother pitched in because they want to “know more about why Tess is the way she is.” So far, according to Peter Kearns, the four have earned more than $300 after only a couple of weekends selling lemonade.

The boys said what’s most fun about the lemonade stand is being outside, working with their friends on the project and earning money for a good cause.

Kate Irish Collins can be reached at 710-2336 or [email protected]. Follow Kate on Twitter: @KIrishCollins.

Patrick McCrann, far right, runs a lemonade stand with his neighbors Peter and Jonathan Kearns to raise money for medical expenses incurred by McCrann’s cousin, Tess Bigelow.

Tess Bigelow, 8, has a rare gene mutation that’s caused severe neurodevelopmental delays, which is why her parents, Bo Bigelow and Kate McCrann, have created the Foundation for USP7 Related Diseases. Also pictured is Tess’ older brother, Dana Bigelow.