Is Opitz G/BBB syndrome inherited ?
When caused by mutations in the MID1 gene, Opitz G/BBB syndrome has an X-linked pattern of inheritance. It is considered X-linked because the MID1 gene is located on the X chromosome, one of the two sex chromosomes in each cell. In males, who have only one X chromosome, a mutation in the only copy of the gene in each cell is sufficient to cause the condition. In females, who have two copies of the X chromosome, one altered copy of the gene in each cell can lead to less severe features of the condition or may cause no symptoms at all. Because it is unlikely that females will have two altered copies of the MID1 gene, females with X-linked Opitz G/BBB syndrome typically have hypertelorism as the only sign of the disorder. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.  Rarely, Opitz G/BBB syndrome is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. These cases are caused by a mutation in the SPECC1L gene or by a deletion of genetic material from one copy of chromosome 22 in each cell. Males and females with autosomal dominant Opitz G/BBB syndrome usually have the same severity of symptoms.  In both types of Opitz G/BBB syndrome, some affected people inherit the genetic change from an affected parent. Other cases may result from new mutations. These cases occur in people with no history of the disorder in their family.