Expanding the known phenotype of Mullegama–Klein–Martinez syndrome in male patients

Here, we report a novel case of a male patient with a hemizygous missense variant in STAG2 (p.Tyr159His) resulting in Mullegama–Klein–Martinez syndrome (MKMS), a rare X-linked cohesinopathy. He shares distinct clinical features with a previously reported male patient carrying the STAG2 variant p.Tyr159Cys, suggesting that this phenotype is determined by the position of the mutation. Additionally, our patient exhibits symptoms not previously associated with MKMS, expanding the known clinical phenotype of this rare disease.