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.

Bi-allelic variants in COLEC11 and MASP1 have been associated with 3MC syndrome, a clinical entity made of up four rare autosomal recessive disorders: Carnevale, Mingarelli, Malpuech, and Michels syndromes, characterized by variable expression of facial dysmorphia, cleft lip/palate, postnatal growth deficiency, hearing loss, cognitive impairment, craniosynostosis, radioulnar synostosis, and genital and vesicorenal anomalies. More recently, bi-allelic variants in COLEC10 have been described to be associated with 3MC syndrome. Syndromic features seen in 3MC syndrome are thought to be due to disruption of the chemoattractant properties that influence neural crest cell migration. We identified nine individuals from five families of Ashkenazi Jewish descent with homozygosity of the c.311G > T (p.Gly104Val) variant in COLEC10 and phenotype consistent with 3MC syndrome. Carrier frequency was calculated among 52,278 individuals of Jewish descent. Testing revealed 400 carriers out of 39,750 individuals of Ashkenazi Jewish descent, giving a carrier frequency of 1 in 99 or 1.01%. Molecular protein modeling suggested that the p.Gly104Val substitution alters local conformation. The c.311G > T (p.Gly104Val) variant likely represents a founder variant, and homozygosity is associated with features of 3MC syndrome. 3MC syndrome should be in the differential diagnosis for individuals with short stature, radioulnar synostosis, cleft lip and cleft palate.

The 3MC syndrome is a rare autosomal recessive syndrome characterized by facial dysmorphism, multiple congenital abnormalities, and postnatal growth deficiency. Hypertelorism, blepharophimosis, blepharoptosis, high-arched eyebrows, and cleft lip/palate compose the facial gestalt, which is the key component for diagnosing the syndrome. Biallelic pathogenic variants in MASP1, COLEC11, and COLEC10 are responsible for 3MC syndrome in which both genotypic and phenotypic heterogeneity is described. To date, 16 homozygous/compound heterozygous pathogenic variations in 27 patients from 22 families have been reported in the MASP1 gene associated with 3MC syndrome. Here, we report a male patient with a novel homozygous pathogenic variant in MASP1 in whom macrocephaly, pyloric stenosis, and prenatal findings including polyhydramnios, aortic dilatation, and intracranial cysts beside the distinctive facial features were detected. Reporting detailed clinical and molecular findings in patients is pivotal in terms of enabling the phenotypic and genotypic spectrum of this rare syndrome to be delineated.

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.