The Holt-Oram syndrome is an autosomal dominant condition characterized by skeletal abnormalities that are frequently accompanied by congenital cardiac defects. The cause of these disparate clinical features is unknown. To identify the chromosomal location of the Holt-Oram syndrome gene, we performed clinical and genetic studies.
Two large families with the Holt-Oram syndrome were evaluated by radiography of the hands, electrocardiography, and transthoracic echocardiography. Genetic-linkage analyses were performed with polymorphic DNA loci dispersed throughout the genome to identify a locus that was inherited with the Holt-Oram syndrome in family members.
A total of 19 members of Family A had Holt-Oram syndrome with mild-to-moderate skeletal deformities, including triphalangeal thumbs and carpal-bone dysmorphism. All affected members of Family A had moderate-to-severe congenital cardiac abnormalities, such as ventricular or atrial septal defects or atrioventricular-canal defects. Eighteen members of a second kindred (Family B) had Holt-Oram syndrome with moderate-to-severe skeletal deformities, including phocomelia. Twelve of the affected members had no cardiac defects; six had only atrial septal defects. Genetic analyses demonstrated linkage of the disease in each family to polymorphic loci on the long arm of chromosome 12 (combined multipoint lod score, 16.8). These data suggest odds greater than 10(16):1 that the genetic defect for Holt-Oram syndrome is present on the long arm of chromosome 12 (12q2).
Mutations in a gene on chromosome 12q2 can produce a wide range of disease phenotypes characteristic of the Holt-Oram syndrome. This gene has an important role in both skeletal and cardiac development.