Trigonocephaly-broad thumbs syndrome

Trigonocephaly-broad thumbs syndrome, also known as Say-Barber-Biesecker-Young-Simpson syndrome or Ohdo syndrome (SBBYS variant), is an extremely rare genetic disorder characterized by a distinctive combination of craniofacial anomalies and limb abnormalities. The hallmark features include trigonocephaly (a triangular shape of the forehead due to premature fusion of the metopic suture), broad thumbs and great toes, and intellectual disability. Affected individuals typically present with blepharophimosis (narrowing of the eye openings), a mask-like facial appearance with a fixed facial expression, and small mouth. Additional features may include short stature, hearing loss, congenital heart defects, and joint abnormalities. The condition primarily affects the skeletal system (particularly the skull and digits), the central nervous system (causing developmental delay and intellectual disability), and the cardiovascular system. Facial features are often distinctive and include a flat nasal bridge, thin upper lip, and low-set ears. Some patients may also exhibit hypotonia (decreased muscle tone) and feeding difficulties in infancy. This syndrome has been associated with mutations in the KAT6B gene (also known as MORF or MYST4), which encodes a histone acetyltransferase involved in chromatin remodeling and gene regulation. The condition follows an autosomal dominant inheritance pattern, with most cases arising from de novo (new) mutations. Treatment is supportive and symptomatic, involving a multidisciplinary approach that may include craniofacial surgery for trigonocephaly, cardiac surgery if heart defects are present, hearing aids for hearing loss, speech therapy, physical therapy, and special educational support for developmental delays. Regular monitoring by a team of specialists is recommended.

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