A 15-year-old girl has developed multiple nodules on her skin over the past 10 years. On physical examination, there are 20 scattered, 0.3-cm to 1-cm, firm nodules on the patient's trunk and extremities. There are 12 light brown macules averaging 2 to 5 cm in diameter on the skin of the trunk. Slit-lamp examination shows pigmented nodules in the iris. A sibling and a parent are similarly affected. Genetic analysis shows a loss-of-function mutation. Which of the following inheritance patterns is most likely to be present in this family?

Neurofibromatosis type 1 (NF-1) is characterized by the development of multiple neurofibromas and pigmented skin lesions. Neurofibromas are most numerous in the dermis but also may occur in visceral organs. Patients with NF-1 also may develop a type of sarcomatous neoplasm known as a malignant peripheral nerve sheath tumor (MPNST). NF-1 is a tumor suppressor that appears with an autosomal dominant pattern of inheritance, though some cases result from spontaneous new mutations (no prior family members with the mutation). NF-1 exhibits variable expressivity, because the manifestations (location and types of neoplasms) are not the same in all patients. The other forms of inheritance listed are not associated with tumor suppressor genes.