When Danny was born, it was discovered that he carried the Fragile X gene, which caused him to be born with a mental handicap. A few years after his birth, his parents Cody McCall and Evelyn Bass decided that they wanted another child, but they didn’t want to risk having another child naturally. They feared that if they had another child naturally, that child could also inherit the gene and develop a mental handicap. Cody and Evelyn could not afford to provide for two children, with a mental handicap, so they decided to adopt instead of having another child naturally.
After making the decision to adopt, they soon brought home a newborn baby girl that they named Samantha. When Sam was only three years old, Evelyn decided that she didn’t want Sam anymore and she no longer wanted to deal with Cody’s drifter ways. So Evelyn left Sam with Cody and took Danny when she moved to Bailey’s Beach, Rhode Island. Evelyn was very distant and emotionally abusive towards Danny because of his mental handicap. No longer wanting to deal with him, she kept Danny locked up in the basement, while she went on with her daily life.
When Sam grew up and was a teen, Cody told her all about Evelyn and Danny. Wanting to confront her mother for abandoning her, Sam set out to find her and ended up in Bailey’s Beach. When Sam went into her mother’s house and began to look around, she was horrified to find her brother Danny chained up in the basement. She quickly unchained him and helped him escape, promising him that she would care for him and give him a better life. As they were sneaking out of the house Danny accidentally knocked over a candle that set the house ablaze with fire. Sam and Danny had no idea that their mother was inside the house when it burnt down and she was killed.
After leaving Bailey’s Beach, Danny and Sam went on with their lives and Sam did the best that she could to care for herself and Danny and give her brother a good life. Years later, the night of the fire came back to haunt them, when Sam was charged with setting the fire that killed their mother, when in actuality it was Danny who had knocked over the candle and started the fire. Wanting to protect her brother, Sam confessed and took the blame for starting the fire that killed their mother. After a few months of being on the run and hiding, Sam's close friend and future lover, mobster Jason Morgan was able to get the charges against Sam dropped, by paying an inmate on death row to confess to starting the fire. Both Sam and Danny were now in the clear and able to move on with their lives. Jason also graciously arranged for Danny to attend a specialized school in Hawaii. However, Danny misunderstood his sister’s intentions and believing that she was trying to send him away he harbored resentment towards her and refused contact with Sam.
In October 2005, Jason and Sam moved to Hawaii to start their new life together. While there Sam and Danny reconciled and Sam was able to explain to Danny that she wasn’t trying to send him away, but only wanted to provide a better life for him. Danny understood and forgave his little sister. Sam and Danny enjoyed their time together in Hawaii until Jason and Sam had to move back to Port Charles, because of a mob threat in the form of the sinister Ruiz family.
In February 2006, Danny returned to Port Charles just in time for an encephalitis epidemic. Sam quickly fell ill, and after caring for her in the hospital, so did Danny. An antidote was found, but there was only enough to be given to one person and the two candidates were Alexis Davis and Danny. Alexis was given the dose and Sam grieved for the loss of her brother. The dying Danny told Sam how glad he was that their parents "chose her," to be his little sister, leading Sam to the discovery that she and Danny were not biological siblings and she was adopted into the McCall family. Sam and Danny shared a sad and tearful goodbye, and as Danny was dying he told Sam that he could hear the angels and could see his niece, Sam’s late daughter Lila McCall coming to greet him. After Danny died, Sam held his favorite red baseball cap near and dear to her heart.
Danny made one last appearance in the form of a vision in May 2006 after Sam was shot and almost died. In the vision Sam had to choose between dying and going with Danny or fighting to live and embracing her new family, which included her two new little sisters Kristina Corinthos-Davis and Molly Lansing-Davis and a woman she hated, Alexis Davis, who was revealed to be Sam’s biological mother. Ultimately Sam chose to fight to live, and recovered from her comatose state.
In 2012, Sam gave birth to a son that she named Danny in memory of her brother.
On February 21, 2014 (22 on the show), eight years since Danny passed away, Sam's biological father, Julian Jerome made a donation to the Fragile X foundation in Danny's name and gave the certificate to Sam.