Axial spondylometaphyseal dysplasia is also caused by NEK1 mutations

Axial spondylometaphyseal dysplasia (axial SMD) is a unique form of SMD characterized by dysplasia of axial skeleton and retinal dystrophy. Recently, C21orf2 has been identified as the first disease gene for axial SMD; however, the presence of genetic heterogeneity is known. In this study, we identified NEK1 as the second disease gene for axial SMD. By whole-exome sequencing in a patient with axial SMD, we identified compound heterozygous mutations of NEK1, c.3107C>G (p.S1036∗) and c.3830A>C (p.D1277A), which co-segregated in the family. NEK1 mutations have previously been found in three types of short rib thoracic dystrophy, which have no retinal dystrophy. The skeletal phenotype of our patient was milder than those of previously reported cases with NEK1 mutations and those with axial SMD harboring C21orf2 mutations. Phenotypes associated with NEK1 mutations are variable and the phenotype-genotype corelation in skeletal ciliopathies is challenging.