Opitz G/BBB syndrome is classified into two types based on genetic mutation and inheritance patterns: X-linked Opitz syndrome, which is caused by a mutation in a specific gene MID1 (midline 1) on chromosome X, and autosomal dominant Opitz G/BBB syndrome, which is caused by a deletion of 22q11.2. The gene discussed is MID1; the disease is Opitz G/BBB syndrome.