CARIBOU, Maine — Six months ago, as those around them ushered in the dawning of another new year, the family of 4-year-old Zyen Provost of Caribou was admittedly becoming discouraged again.

In January 2012, Zyen was diagnosed with XLP, short for X-linked lymphoproliferative syndrome, also known as Duncan’s syndrome. This genetic defect is found in boys and causes the immune system to respond abnormally to some viral infections, resulting either in an underactive or overactive immune system. The disease is seen so infrequently that only approximately 400 boys have been diagnosed worldwide, according to the XLP Research Trust.

If untreated, approximately 70 percent of patients with XLP die by the age of 10. Currently, the only cure is a stem cell transplant, a procedure that Zyen underwent at Boston Children’s Hospital on May 31.

“In January, the doctors were telling us that they were questioning whether the stem cell transplant worked or not,” his great-grandmother, Karyn Pinette of Caribou, said on Thursday. “So we thought that we might have to go through the whole process again. We were planning another fundraiser and getting ready for another transplant and anticipating the worst.”

Then, all of a sudden, they heard, “the best news ever.”

“He no longer has the disease,” Pinette said. “His DNA is 97 percent donor cells, which is excellent. We just found this out in April.”

Because of the success of the stem cell transplant, the life that Zyen had to put on hold when he got sick can now move forward. He is excited to attend afternoon preschool in the fall and loves to learn new things.

“He is like a little sponge,” she said. “He just soaks everything up. He loves to play legos and educational games.”

Zyen has involved parents in Kristopher Ginn, Pinette’s grandson, and Jessica Provost, Zyen’s mother. Pinette said that she and her husband, Ryan Pinette, still have Zyen living with them at their home. The family received tremendous support from community members and businesses who helped with fundraisers and donations during Zyen’s illness.

When he was recovering from the transplant, Zyen was not allowed to go far beyond the hospital grounds and his home. Now, he is having fun exploring all kinds of different places.

“We took him into a grocery store, and he was shocked by all of the different things that he saw,” Pinette said. “He hadn’t been in one since he was 12 months old. Its funny, seeing all of it through his eyes. And seeing how he is at the playground. He is off all of his medications and he isn’t trapped inside the house anymore.

“He loves going outside, and we are all so happy to have such a positive outcome has been outstanding,” she continued. “We all love seeing Zyen running around like he is. He’s all boy.”