A 4-year-old boy is brought to the pediatric clinic by his parents, who are concerned about multiple light brown spots on his skin that they have noticed since birth. The boy has no developmental delays or other complaints. On examination, he has 8 café-au-lait spots, each measuring ~1 cm in diameter, along with freckling in the axillary region. His father also has similar skin lesions and a history of benign skin tumors. Which of the following is most strongly associated with the presence of multiple café-au-lait spots in this child?
