Opitz G/BBB syndrome, MID1-related (also called MID1-OS), is a condition that causes multiple birth defects and intellectual disability predominantly in individuals assigned male at birth.
Symptoms of MID1-OS include unique facial features and birth defects in areas like the throat, genitals, heart, and brain. Some people with this condition also have a cleft lip or palate. More than 30% of individuals may have developmental delays or intellectual disabilities. The severity of symptoms can vary a lot, even within the same family. Almost everyone with MID1-OS has facial differences, such as eyes that are farther apart than usual (hypertelorism). Other common facial features include a wide nose bridge, a prominent forehead, and low-set ears.
There is no cure for Opitz G/BBB syndrome. Treatment focuses on managing the specific symptoms a person has. Many of the birth defects can be treated with surgery. Early intervention and supportive services can help those with developmental delays.
Opitz G/BBB syndrome is caused by pathogenic variants in the MID1 gene and exhibits X-linked recessive inheritance. This means that one pathogenic variant is enough to cause the disease in both individuals assigned male at birth (who have one X chromosome and one Y chromosome) and individuals assigned female at birth (who have two X chromosomes) may experience symptoms depending on how many copies of the X chromosome that has the pathogenic variant are turned on in the cells.
Individuals assigned female at birth (XX) are considered carriers and usually do not have disease symptoms, but they may have increased distance between the eyes (hypertelorism) with no other symptoms.
Resources:
National Organization for Rare Disorders
Written August 2024
