A novel autosomal recessive GJA1 missense mutation linked to Craniometaphyseal dysplasia

Abstract

Craniometaphyseal dysplasia (CMD) is a rare sclerosing skeletal disorder with progressive hyperostosis of craniofacial bones. CMD can be inherited in an autosomal dominant (AD) trait or occur after de novo mutations in the pyrophosphate transporter ANKH. Although the autosomal recessive (AR) form of CMD had been mapped to 6q21-22 the mutation has been elusive. In this study, we performed whole-exome sequencing for one subject with AR CMD and identified a novel missense mutation (c.716G>A, p.Arg239Gln) in the C-terminus of the gap junction protein alpha-1 (GJA1) coding for connexin 43 (Cx43). We confirmed this mutation in 6 individuals from 3 additional families. The homozygous mutation cosegregated only with affected family members. Connexin 43 is a major component of gap junctions in osteoblasts, osteocytes, osteoclasts and chondrocytes. Gap junctions are responsible for the diffusion of low molecular weight molecules between cells. Mutations in Cx43 cause several dominant and recessive disorders involving developmental abnormalities of bone such as dominant and recessive oculodentodigital dysplasia (ODDD; MIM #164200, 257850) and isolated syndactyly type III (MIM #186100), the characteristic digital anomaly in ODDD. However, characteristic ocular and dental features of ODDD as well as syndactyly are absent in patients with the recessive Arg239Gln Cx43 mutation. Bone remodeling mechanisms disrupted by this novel Cx43 mutation remain to be elucidated.

Figure 1. Pedigree information and case description.

(A) Pedigrees of Families 1, 2 and 3 with mutation in the novel CMD gene GJA1. Proband DNA from Family 1 was used for exome sequencing (Arrow). (B) Radiographic images of proband for Family 3 show hyperostosis of cranial base and facial bones, femoral flaring and undertrabeculation of metaphyses with dense diaphyseal bone consistent with findings in Family 2. Diffuse widening of the proximal and medial phalanges are consistent with findings in CMD patients from Family 2 [18].

Figure 2. Confirmatory sequencing.

Sanger sequencing to confirm exome sequencing data with a mutation in the CONNEXIN 43 gene GJA1 in position c.716G>A (p.Arg239Gln). Data shown for Family 1 (VIII5 proband; VIII3 unaffected sibling; VII5 and VII6 heterozygous parents), Family 2 (V1 proband, V4 affected cousin; IV26 and IV27afffected aunts; V2 and V3 unaffected cousins; IV39 and IV40 heterozygous parents of V1; IV46 and IV47 heterozygous parents of V4) and Family 3 (III11 proband; III12 unaffected sibling; II8 and II9 heterozygous parents).

Figure 3. Phylogenetic comparison of GJA1 across species.

Position of the mutation within a highly conserved region indicated with arrow.

Figure 4. Domain structure of CONNEXIN 43.

The CX43 protein consists of an intracellular amino acid domain (AT), four transmembrane domains (TM), two extracellular loops and one intracellular loop. The novel CMD mutation is indicated as a red dot in the carboxyl-terminal domain (CT).