Exome sequencing identifies an MYH3 mutation in a family with distal arthrogryposis type 1

Abstract

Background: Few genes responsible for distal arthrogryposis type 1 are known, although genes coding for the proteins in the sarcomere have been implicated in other types of distal arthrogryposis. Cost-effective sequencing methods are now available to examine all genes in the human genome for the purpose of establishing the genetic basis of musculoskeletal disorders.

Methods: A multigenerational family with distal arthrogryposis type 1 characterized by clubfoot and mild hand contractures was identified, and exome sequencing was performed on DNA from one of the affected family members. Linkage analysis was used to confirm whether a genetic variant segregated with distal arthrogryposis.

Results: Exome sequencing identified 573 novel variants that were not present in control databases. A missense mutation in MYH3 (a gene coding for the heavy chain of myosin), causing an F437I amino acid substitution, was identified that segregated with distal arthrogryposis in this family. Linkage analysis confirmed that this MYH3 mutation was the only exome variant common to all six affected individuals.

Conclusions: Identification of an MYH3 mutation in this family with distal arthrogryposis type 1 broadens the phenotype associated with MYH3 mutations to include distal arthrogryposis types 1, 2A (Freeman-Sheldon syndrome), and 2B (Sheldon-Hall syndrome). Exome sequencing is a useful and cost-effective method to discover causative genetic mutations, although data from extended families may be needed to confirm the importance of the hundreds of identified variants.

Fig. 1

Distal limb contractures in family members with distal arthrogryposis type 1. A: The feet of the proband (identified as III:3 in Fig. 2), showing unilateral clubfoot of the left foot. B: The feet of the proband after correction of the clubfoot with use of the Ponseti method, showing limited residual deformity at the age of seven years. C: Proximally placed thumbs and distal interphalangeal joint contractures in an aunt of the proband (identified as II:7 in Fig. 2). D: Camptodactyly in the father of the proband (identified as II:9 in Fig. 2).

Fig. 2

Pedigree of the family, showing members with and without distal arthrogryposis type 1. Black shading indicates clubfoot, and asterisks indicate hand contractures. The presence of the MYH3 F437I mutation is indicated by “Mut,” and its absence is indicated by “WT.”

Fig. 3

Alignment of MYH3 amino acids surrounding the location corresponding to the F437I mutation in sequences from multiple species. The phenylalanine at residue 437 is indicated by the rectangle and is conserved across all of the species shown, including mouse, rat, human, cow, frog, and chicken. The sequences were aligned with use of the CLUSTALW program (http://align.genome.jp).

Fig. 4

Ribbon diagram of the MYH3 S2 (myosin head) region containing amino acids 4 through 1022. The location of the MYH3 F437I mutation identified in the family with distal arthrogryposis type 1 is shown in orange. The locations of five other known mutations causing distal arthrogryposis type 2A (Freeman-Sheldon syndrome) are shown in red; four of these are in the myosin head and lie in the groove that forms the ATP binding site. The image was generated by the Swiss-PDBViewer (DeepView) program (http://ca.expasy.org/spdbv) for protein accession number P11055 (MYH3).

Fig. 5

Linkage of distal arthrogryposis type 1 to chromosome 17p. A genome-wide profile of parametric multipoint LOD (logarithm of odds) scores for the family with distal arthrogryposis type 1, constructed from the Affymetrix 10K array data. The human chromosomes, running from the p terminal (left) to the q terminal (right), are concatenated on the horizontal axis. The vertical axis shows the parametric LOD score for the physical locations on the human chromosome indicated on the horizontal axis. The peak LOD (pLOD) score (defining the strongest region of linkage) of 1.86 was within chromosome 17p.