The gene that is mutated in this syndrome (SBDS) lies on the long arm of chromosome 7 at cytogenetic position 7q11.  It is composed of five exons and has an associated mRNA transcript that is 1. 6 kilobase pairs in length. The SBDS gene resides in a block of genomic sequence that is locally duplicated on the chromosome. The second copy contains a non-functional version of the SBDS gene that is 97% identical to the original gene, but has accumulated inactivating mutations over time.