Blepharophimosis-intellectual disability syndrome, SBBYS type

Blepharophimosis-intellectual disability syndrome, SBBYS type (also known as Say-Barber-Biesecker-Young-Simpson syndrome or Ohdo syndrome, SBBYS variant) is a rare genetic disorder caused by mutations in the KAT6B gene (also known as MYST4), which encodes a histone acetyltransferase involved in gene regulation. The condition is characterized by a distinctive facial appearance including blepharophimosis (narrowing of the eye openings), ptosis (drooping eyelids), and a mask-like, immobile face. Affected individuals typically present with intellectual disability ranging from mild to severe, significant speech and language delay, and hypotonia (low muscle tone). Additional features may include long thumbs and great toes, patellar hypoplasia or aplasia (underdeveloped or absent kneecaps), hearing loss, congenital heart defects, dental anomalies, hypothyroidism, and cryptorchidism in males. The condition affects multiple body systems including the craniofacial structures, musculoskeletal system, central nervous system, endocrine system, and cardiovascular system. Growth may be impaired, and feeding difficulties are common in infancy. Thyroid dysfunction, particularly hypothyroidism, is a notable endocrine feature that requires monitoring. There is currently no cure for SBBYS-type blepharophimosis-intellectual disability syndrome. Management is supportive and multidisciplinary, involving ophthalmologic interventions for blepharophimosis and ptosis, speech and physical therapy, hearing aids if needed, thyroid hormone replacement for hypothyroidism, cardiac monitoring and surgical correction of heart defects when indicated, and special educational support. Early intervention programs are recommended to optimize developmental outcomes. Regular follow-up with multiple specialists is essential for comprehensive care.

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