Expansion of the 3MC Syndrome Spectrum: Novel COLEC10 Variants and a MASP1 Exon-Level Deletion.

3MC syndrome is a rare congenital malformation disorder caused by biallelic pathogenic variants in COLEC10, COLEC11, and MASP1. It is characterized by distinctive craniofacial anomalies, growth retardation, developmental delay, and variable systemic findings. Here, we report seven previously unreported patients with 3MC syndrome from five unrelated families. The cohort included five females and two males, aged 1-10 years. All patients exhibited characteristic craniofacial features, including hypertelorism, blepharoptosis, highly arched eyebrows, and epicanthus inversus. Cleft lip and/or palate were present in six patients, caudal appendage in four, congenital heart disease in two, hearing loss in four, and periumbilical anomalies in six. All patients showed neuromotor developmental delay. Molecular analysis identified novel pathogenic variants in COLEC10 in five patients and pathogenic alterations in MASP1 in two patients, including an exon-level deletion. These findings expand the clinical and molecular spectrum of 3MC syndrome and highlight the value of comprehensive molecular testing in its diagnosis.