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3MC syndrome is an autosomal recessive disorder encompassing four rare disorders previously known as the Malpuech, Michels, Mingarelli and Carnevale syndromes. They are characterized by a variable spectrum of abnormalities, including facial dysmorphisms, along with genital, limb and vesico-renal anomalies. The syndrome was originally attributed to mutations in MASP1 and COLEC11 , which code for proteins involved in the lectin complement pathway. More recently, mutations in COLEC10 , a third gene coding for collectin CL-L1, were identified in a limited number of patients with 3MC syndrome. Here we describe a 4-years-old patient with typical 3MC phenotypic characteristics, including blepharophimosis, telecanthus, high arched eyebrows, fifth finger clinodactyly, sacral dimple and horseshoe kidney. Initial genetic analysis was based on clinical exome sequencing, where only MASP1 and COLEC11 genes are present, without evidence of pathogenic variants. Sanger sequencing of COLEC10 identified the homozygous frameshift variant c.807_810delCTGT; p.Cys270Serfs*33, which results in the loss of the natural stop codon. The resulting protein is 24 amino acids longer and lacks a conserved cysteine residue (Cys270), which could affect protein folding. Segregation studies confirmed that both parents were carriers for the variant: interestingly they originate from the same area of Apulia in southern Italy. Plasma levels of CL-L1 in the patient and her parents were within normal range, suggesting that this variant does not modify transcription or secretion. However, the variant affects the chemo-attractive feature of CL-L1, as HeLa cells migrate significantly less in response to the mutant protein compared to the wild-type one. [ABSTRACT FROM AUTHOR]