Identification of a novel FBN1 gene mutation in a Chinese family with Marfan syndrome

Abstract

Purpose: To identify the mutation in the fibrillin-1 gene (FBN1) in a Chinese family with Marfan syndrome (MFS).

Methods: Patients and family members were given complete physical, ophthalmic, and cardiovascular examinations. Genomic DNA was extracted from leukocytes of venous blood of six individuals in the family and 170 healthy Chinese individuals. All of the 65 coding exons and their flanking intronic boundaries of FBN1 were amplified in the proband by polymerase chain reaction and followed by direct sequencing. The mutation identified in the proband was screened in the other family members and the 170 healthy Chinese individuals by direct sequencing. Protein conservation analysis was performed in six species using an online ClustalW tool. Protein structure was modeled based on the Protein data bank and mutated in DeepView v4.0.1 to predict the functional consequences of the mutation.

Results: A novel heterozygous c.3703T>C change in exon 29 of FBN1 was detected in the proband, which resulted in the substitution of serine by proline at codon 1235 (p.S1235P). This mutation was also present in two family members but absent in the other, unaffected family members and the 170 healthy Chinese individuals. The mutant residue located in the calcium binding epidermal growth factor-like#15 domain is highly conserved among mammalian species and could probably induce conformation change of the domain.

Conclusions: We indentified a novel p.S1235P mutation in FBN1, which is the causative mutation for MFS in this family. Our result expands the mutation spectrum of FBN1 and contributes to the study of the molecular pathogenesis of Marfan syndrome.

Figure 1

The pedigree of the family. Squares and circles indicate males and females, respectively, and the darkened symbols represent the affected members. Slashed symbols denote that the subject is deceased. Symbols with a question mark in the center indicate that the member is not diagnosed clearly. Asterisks indicate the subjects participating in this study. The patient indicated by the arrow is the proband.

Figure 2

Photographs of the proband. A and B display the slit lamp photographs of both of the proband’s eyes after the pupils were dilated, showing ectopia lentis. In the right eye (A), the lens is dislocated nasally. In the left eye (B), the lens is dislocated superonasally. C shows arachnodactyly of the proband.

Figure 3

A novel FBN1 mutation in exon 29. A-C show a heterozygous T>C transition (indicated by the arrow) resulting in the substitution of serine by proline (S1235P) in the proband, patient II:2, and the proband’s daughter, IV:4, respectively. D-F show the corresponding normal sequence in unaffected family members II:7 and III:4 and spouse II:6, respectively. G shows the corresponding normal sequence in a healthy member. H displays the sequence alignment of FBN1 orthologs surrounding the mutated site using ClustalW. The serine1235 of the human FBN1 protein is highly conserved in several species. These sequences were selected from the NCBI database.

Figure 4

Structure analyses of the missense mutation in the calcium binding (cb) epidermal growth factor (EGF)-like#15 domain. A displays the location of the affected module in the neonatal region of the fibrillin-1 domain structure. B displays the consensus secondary structure of a prototypical cb EGF-like domain. Calcium binding in the NH₂-terminal region of the wild-type domain is mediated by the consensus sequence (D/N)-X-(D/N)(E/Q)Xm(D/N)Xn(Y/F) (m and n are variables), and highly conserved amino acids are identified by their single-letter amino acid code. Letter C in the schematic represents the highly conserved cysteines of cb EGF-like domain, and the lines between cysteines represent disulfide bridges. The mutation S1235P is located at the 39th residue of the domain, which neither interferes with calcium binding of the domain nor influences disulfide bond formation. C displays the 3D structure of the cb EGF-like#15 domain, which is created based on the Protein data bank (PDB) template 1LMJ (45% sequence identity) by DeepView v4.0.1. The yellow lines represent disulfide bonds, and the purple residue represents the unaffected serine. D displays the potential consequence of the mutation. The purple residue represents the substitute proline, and the purple dashed lines mean steric clash with surroundings, which may lead to unstable conformation.