This clinical vignette describes a patient with Huntington's disease. Huntington's disease has an autosomal dominant hereditary pattern with anticipation. Anticipation is a term used to describe trinucleotide repeat disorders that if passed on, will present earlier and more severely in affected subjects than their than affected parent. In Huntington's disease, it is due to a "CAG" trinucleotide repeat on chromosome 4. Subjects with an affected parent have a 50% chance of inheriting the disease from them, and if present will have more severe disease.
Deighton et al provide a review on the genetics of musculoskeletal disease including the hereditary pattern of anticipation.
Deighton CM, Thomson G. Genetic anticipation and musculoskeletal disease. Ann Rheum Dis. 1994 Dec;53(12):787-8
PMID:7864684 (Link to Abstract)
Cole WG. Genetic aspects of orthopaedic conditions. In: Morrissy RT, Weinstein SL, eds. Lovell and Winter's Pediatric Orthopaedics. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006:145-165.