Ohdo syndrome, SBBYS variant(redirected from Young-Simpson syndrome)
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Ohdo syndrome, SBBYS variantAn extremely rare (30 cases in the world literature), multi-system, possibly autosomal recessive malformation complex (OMIM:603736) characterised by microcephaly, distinct facies, severe blepharophimosis, an immobile mask-like face, a bulbous nasal tip, and a small mouth with a thin upper lip. It presents in infancy with severe hypotonia and feeding problems. Associated skeletal problems include joint laxity, abnormally long thumbs and great toes, and dislocated or hypoplastic patellae. Structural cardiac defects are present in around 50% of cases, as well as dental anomalies such as small and pointed teeth. Affected individuals may have defects in thyroid structure or function. SBBYSS is usually associated with severe mental retardation, delayed motor milestones, significantly impaired speech, hearing impairment, abnormal ears and growth retardation. Male patients may have cryptorchidism and scrotal hypoplasia.
Defects in KAT6B, which encodes a histone acetyltransferase that can either up- or downregulate transcription, cause Ohdo syndrome.