FREM1 mutations cause bifid nose, renal agenesis, and anorectal malformations syndrome

Abstract

An autosomal-recessive syndrome of bifid nose and anorectal and renal anomalies (BNAR) was previously reported in a consanguineous Egyptian sibship. Here, we report the results of linkage analysis, on this family and on two other families with a similar phenotype, which identified a shared region of homozygosity on chromosome 9p22.2-p23. Candidate-gene analysis revealed homozygous frameshift and missense mutations in FREM1, which encodes an extracellular matrix component of basement membranes. In situ hybridization experiments demonstrated gene expression of Frem1 in the midline of E11.5 mouse embryos, in agreement with the observed cleft nose phenotype of our patients. FREM1 is part of a ternary complex that includes FRAS1 and FREM2, and mutations of the latter two genes have been reported to cause Fraser syndrome in mice and humans. The phenotypic variability previously reported for different Frem1 mouse mutants suggests that the apparently distinct phenotype of BNAR in humans may represent a previously unrecognized variant of Fraser syndrome.

Figure 1

Mutations in FREM1 are Responsible for Bifid Nose, Renal Agenesis, and Anorectal Malformations Syndrome (A) A representative BNAR patient from each of the two new families described in this report (note the discoloration at the tip of the nose that was observed in a subset of patients). (B) Chromatograms of the three mutations showing control sequences on top, with the mutation sites denoted by asterisks. (C) Multiple sequence alignments of the FREM1 protein reveal that the amino acids perturbed by the two missense mutations are highly conserved across species. (D) Schematic of the FREM1 protein indicating conserved domains and the location of mutations given in (B) (arrows), as well as truncating mutations that have been reported in mice (arrowheads). CSPG, chondroitin sulfate proteoglycan; LecC, type C lectin-like domain.

Figure 2

Frem1 Is Expressed in the Developing Nose (A) RNA in situ hybridization experiment showing strong expression in the snout region of an E11.5 mouse. (B) Inferior view along the plane of the dotted line in (A) showing strong expression at midline (x8). (C and D) Section of (A) showing strong expression at the area of fusion of the two medial nasal processes (x20) (C), and the sense control for comparison (D).