Novel FREM1 mutations in a patient with MOTA syndrome: Clinical findings, mutation update and review of FREM1-related disorders literature

Two novel mutations within FREM1 gene in patients with bifid nose

BACKGROUND

Bifid nose is a rare congenital deformity and the etiology is unknown. The purpose of this study was to report genetic variation in family of patients with bifid nose.

METHODS

Twenty-three consecutive patients who were diagnosed with mild bifid nose were operated with z-plasty from 2009 to 2021. Three underage patients (a pair of twins and a girl) from two family lines, who came to our hospital for surgical treatment, were enrolled. Whole exome sequencing and Sanger sequencing were conducted. Z-shaped flaps were created and the cartilago alaris major were re-stitched. Photographs and CT scan before and after surgery were obtained. Clinical outcomes, complications and patients' satisfaction were evaluated and analyzed. The follow-up time ranges from 2 to 3 years (2.4 ± 1.2 years).

RESULTS

Most patients were satisfied with the outcome (96.2%). The nasal deformities were corrected successfully with z-plasty technique in one-stage. FREM1 c.870_876del and c.2 T > C were detected with Whole exome sequencing, which have not been reported before. The results of Sanger sequencing were consistent with those of Whole exome sequencing.

CONCLUSIONS

The newly detected mutations of FREM1 have a certain heritability, and are helpful to make an accurate diagnosis and provide a better understanding of bifid nose mechanism. Z-plasty technique can be an effective technical approach for correcting mild bifid nose deformity.

Cryptophthalmos: associated syndromes and genetic disorders

PURPOSE

Cryptophthalmos is a rare congenital condition caused by anomalous eyelid development where the eyelid folds do not develop or fail to separate. Cryptophthalmos can be unilateral or bilateral and can occur in isolation or as part of an underlying syndrome. We aim to identify genetic syndromes associated with cryptophthalmos to facilitate genetic diagnosis.

METHODS

We performed a retrospective medical record review of all patients diagnosed with cryptophthalmos followed at a single center between 2000 and 2020. The analysis included medical history, clinical examination findings, and genetic testing results.

RESULTS

Thirteen patients were included, 10 (77%) males, mean age of 2.4 years. Eight (61%) had bilateral cryptophthalmos, and 4 (31%) had complete cryptophthalmos. Associated ocular abnormalities included corneal opacities (13/13, 100%), upper eyelid colobomas (12/13, 92%), and microphthalmia/clinical anophthalmia (3/13, 23%). All cases of complete cryptophthalmos had bilateral disease. An underlying clinical or molecular diagnosis was identified in 10/13 (77%) cases, including Fraser syndrome (n = 5), amniotic band syndrome (n = 1), FREM1-related disease (n = 1), Goldenhar versus Schimmelpenning syndrome (n = 1), MOTA syndrome (n = 1), and CELSR2-related disease (n = 1).

CONCLUSION

This is the first report of a possible association between cryptophthalmos and biallelic CELSR2 variants. Children with cryptophthalmos, especially those with extra-ocular involvement, should be referred for comprehensive genetic evaluation.

Frem1 activity is regulated by Sonic hedgehog signaling in the cranial neural crest mesenchyme during midfacial morphogenesis

BACKGROUND

Frem1 has been linked to human face shape variation, dysmorphology, and malformation, but little is known about its regulation and biological role in facial development.

RESULTS

During midfacial morphogenesis in mice, we observed Frem1 expression in the embryonic growth centers that form the median upper lip, nose, and palate. Expansive spatial gradients of Frem1 expression in the cranial neural crest cell (cNCC) mesenchyme of these tissues suggested transcriptional regulation by a secreted morphogen. Accordingly, Frem1 expression paralleled that of the conserved Sonic Hedgehog (Shh) target gene Gli1 in the cNCC mesenchyme. Suggesting direct transcriptional regulation by Shh signaling, we found that Frem1 expression is induced by SHH ligand stimulation or downstream pathway activation in cNCCs and observed GLI transcription factor binding at the Frem1 transcriptional start site during midfacial morphogenesis. Finally, we found that FREM1 is sufficient to induce cNCC proliferation in a concentration-dependent manner and that Shh pathway antagonism reduces Frem1 expression during pathogenesis of midfacial hypoplasia.

CONCLUSIONS

By demonstrating that the Shh signaling pathway regulates Frem1 expression in cNCCs, these findings provide novel insight into the mechanisms underlying variation in midfacial morphogenesis.

The Potential Role of FREM1 and Its Isoform TILRR in HIV-1 Acquisition through Mediating Inflammation

FREM1 (Fras-related extracellular matrix 1) and its splice variant TILRR (Toll-like interleukin-1 receptor regulator) have been identified as integral components of innate immune systems. The potential involvement of FREM1 in HIV-1 (human immunodeficiency virus 1) acquisition was suggested by a genome-wide SNP (single nucleotide polymorphism) analysis of HIV-1 resistant and susceptible sex workers enrolled in the Pumwani sex worker cohort (PSWC) in Nairobi, Kenya. The studies showed that the minor allele of a FREM1 SNP rs1552896 is highly enriched in the HIV-1 resistant female sex workers. Subsequent studies showed that FREM1 mRNA is highly expressed in tissues relevant to mucosal HIV-1 infection, including cervical epithelial tissues, and TILRR is a major modulator of many genes in the NF-κB signal transduction pathway. In this article, we review the role of FREM1 and TILRR in modulating inflammatory responses and inflammation, and how their influence on inflammatory responses of cervicovaginal tissue could enhance the risk of vaginal HIV-1 acquisition.

Heterozygous intragenic deletions of FREM1 are not associated with trigonocephaly

Recessive mutations in FRAS1-related extracellular matrix 1 (FREM1) are associated with two rare genetic disorders, Manitoba-oculo-tricho-anal (MOTA) and bifid nose with or without anorectal and renal anomalies (BNAR). Fraser syndrome is a more severe disorder that shows phenotypic overlap with both MOTA and anorectal and renal anomalies and results from mutations in FRAS1, FREM2 and GRIP1. Heterozygous missense mutations in FREM1 were reported in association with isolated trigonocephaly with dominant inheritance and incomplete penetrance. Moreover, large deletions encompassing FREM1 have been reported in association with a syndromic form of trigonocephaly and were designated as trigonocephaly type 2. Trigonocephaly results from premature closure of the metopic suture and typically manifests as a form of nonsyndromic craniosynostosis. We report on 20 patients evaluated for developmental delay and without abnormal metopic suture. Chromosomal microarray analysis revealed heterozygous FREM1 deletions in 18 patients and in 4 phenotypically normal parents. Two patients were diagnosed with MOTA and had homozygous FREM1 deletions. Therefore, although our results are consistent with the previous reports of homozygous deletions causing MOTA, we report no association between heterozygous FREM1 deletions and trigonocephaly in this cohort.

Facial cleft? The first case of manitoba-oculo-tricho-anal syndrome with novel mutations in China: a case report

Background

Manitoba-oculo-tricho-anal (MOTA) syndrome is a rare syndrome with only 27 cases reported worldwide so far, but none was reported in the population of Eastern Asia. Such extremely low prevalence might be contributed by misdiagnosis due to its similarities in ocular manifestations with facial cleft. In our study, we discovered the first case of MOTA syndrome in the population of China, with 2 novel FRAS1 related extracellular matrix 1 (FREM1) gene stop-gain mutations confirmed by whole exome sequencing.

Case presentation

A 12-year-old Chinese girl presented with facial cleft-like deformities including aberrant hairline, blepharon-coloboma and broad bifid nose since birth. Whole exome sequencing resulted in the identification of 2 novel stop-gain mutations in the FREM1 gene. Diagnosis of MOTA syndrome was then established.

Conclusions

We discovered the first sporadic case of MOTA syndrome according to clinical manifestations and genetic etiology in the Chinese population. We have identified 2 novel stop-gain mutations in FREM1 gene which further expands the spectrum of mutational seen in the MOTA syndrome. Further research should be conducted for better understanding of its mechanism, establishment of an accurate diagnosis, and eventually the exploitation of a more effective and comprehensive therapeutic intervention for MOTA syndrome.

Toll-like Interleukin 1 Receptor Regulator Is an Important Modulator of Inflammation Responsive Genes

TILRR (Toll-like interleukin-1 receptor regulator), a transcript variant of FREM1, is a novel regulatory component, which stimulates innate immune responses through binding to IL-1R1 (Interleukin-1 receptor, type 1) and TLR (Toll-like receptor) complex. However, it is not known whether TILRR expression influences other genes in the NFκB signal transduction and pro-inflammatory responses. Our previous study identified FREM1 as a novel candidate gene in HIV-1 resistance/susceptibility in the Pumwani Sex worker cohort. In this study, we investigated the effect of TILRR overexpression on expression of genes in the NFκB signaling pathway in vitro. The effect of TILRR on mRNA expression of 84 genes related to NFκB signal transduction pathway was investigated by qRT-PCR. Overexpression of TILRR on pro-inflammatory cytokine/chemokine(s) secretion in cell culture supernatants was analyzed using Bioplex multiplex bead assay. We found that TILRR overexpression significantly influenced expression of many genes in HeLa and VK2/E6E7 cells. Several cytokine/chemokine(s), including IL-6, IL-8 (CXCL8), IP-10, MCP-1, MIP-1β, and RANTES (CCL5) were significantly increased in the cell culture supernatants following TILRR overexpression. Although how TILRR influences the expression of these genes needs to be further studied, we are the first to show the influence of TILRR on many genes in the NFκB inflammatory pathways. The NFκB inflammatory response pathways are extremely important in microbial infection and pathogenesis, including HIV-1 transmission. Further study of the role of TILRR may identify the novel intervention targets and strategies against HIV infection.

A homozygous mutation p.Arg2167Trp in FREM2 causes isolated cryptophthalmos

Cryptophthalmos (CO, MIM: 123570) is rare congenital anomalies of eyelid formation, which can occur alone or in combination with multiple congenital anomalies as part of Fraser syndrome (FS) or Manitoba Oculotrichoanal syndrome. Causal mutations have been identified for these syndromes but not in the isolated cases. Here, we described two patients from two unrelated Chinese families: one with unilateral isolated CO, while the other with unilateral CO and renal agenesis. A novel homozygous mutation (c.6499C>T: p.Arg2167Trp) and compound heterozygote mutations (c.15delG; c.6499C>T: p.Arg2167Trp) in FREM2 (NM_172862) were identified for the two patients, respectively. The deletion mutation c.15delG resulted in a frameshift and triggered the nonsense-mediated mRNA decay. For the shared missense mutation, p.Arg2167Trp altered a conserved residue and was predicted to affect protein structure by in silico analysis. Functional analysis revealed that Arg2167Trp mutant decreased its interaction with FRAS1 related extracellular matrix 1 (FREM1) and impaired the function of the FRAS1-FRAS1 related extracellular matrix 1 (FREM2)-FREM1 ternary complex required for normal embryogenesis. Furthermore, considering that mutation (c.5914C>T: p.Glu1972Lys) in FREM2 causes FS, a severe systemic disorder, we also compared these two different missense mutations. Our results showed that p.Arg2167Trp had a weaker effect in interrupting interactions between FREM2 and FREM1 than FS-associated missense mutation p.Glu1972Lys. Overall, our data demonstrate that the homozygous mutation p.Arg2167Trp in FREM2 causes isolated CO, which will facilitate our better understanding of the molecular mechanisms underlying the disease.