Say-Barber-Biesecker Syndrome, also known as Say-Barber-Biesecker-Young-Simpson (SBBYS) variant, is a variant of a rare genetic condition called Ohdo syndrome. SBBYS causes genital abnormalities in males, missing or underdeveloped kneecaps (patellae), learning problems (intellectual disability), and abnormal facial features. The features of SBBYS are usually noticed in infancy. Males have undescended testes (cryptorchidism) while females have normal genitalia. Infants will also seem floppy, due to low muscle tone (hypotonia), and will also have problems feeding. Along with underdeveloped kneecaps, affected children will also have stiff hip, knee, and ankle joints, while the joints in their upper body may be loose. Affected children may also have long thumbs and big toes. SBBYS causes specific facial features, including prominent cheeks, a wide nasal bridge, and a nose with a rounded tip. SBBYS occurs in less than 1 in a million children.
SBBYS is caused by changes (mutations) within the KAT6B gene and is inherited in an autosomal dominant fashion, meaning a mutation in one of the two KAT6B gene copies a child has is enough to cause the condition. Most cases of SBBYS are caused by a new mutation in the affected child (not inherited from an affected parent). The KAT6B gene is responsible for making an enzyme that modifies the proteins that hold chromosomes together (histones). Scientists believe the gene is important for early development of the skeleton and nervous system. If a doctor suspects SBBYS, they can confirm the diagnosis with genetic testing. Sadly, there is no cure for SBBYS at this time. If your child has been diagnosed with SBBYS, talk with their doctor to discuss treatment options and recommendations. Support groups are a good resource for additional information and to connect with other families affected by SBBYS.