The family investigated showed the presence of multiple genetic disorders among their members. The presumable defective genes were related to coagulation factor X, familial hypercholesterolemia, mitral valve prolapse, and hypertrophic cardiomyopathy. The parents were offspring of two siblings, and their children comprised a nonidentical twin. While the proband demonstrated factor X deficiency, obstructive hypertrophic cardiomyopathy, and primary hypercholesterolemia, her parents and her elder sister were considered heterozygous for factor X. In addition, her mother had elevated plasma cholesterol levels, and her father primary hypercholesterolemia as well as mitral valve prolapse. The twin sister, heterozygous for factor X deficiency, displayed mitral valve prolapse. The clustering of defective genes in this family was considered to represent ‘coincidental’ occurrences rather than being linked to each other.