Nuclear Abnormalities in <i>LMNA</i> p.(Glu2Lys) Variant Segregating with <i>LMNA</i>-Associated Cardiocutaneous Progeria Syndrome

Abstract

The LMNA gene encodes lamin A and lamin C, which play important roles in nuclear organization. Pathogenic variants in LMNA cause laminopathies, a group of disorders with diverse phenotypes. There are two main groups of disease-causing variants: missense variants affecting dimerization and intermolecular interactions, and heterozygous substitutions activating cryptic splice sites. These variants lead to different disorders, such as dilated cardiomyopathy and Hutchinson–Gilford progeria (HGP). Among these, the phenotypic terms for LMNA-associated cardiocutaneous progeria syndrome (LCPS), which does not alter lamin A processing and has an older age of onset, have been described. Here, we present the workup of an LMNA variant of uncertain significance, NM_170707.2 c. 4G>A, p.(Glu2Lys), in a 36-year-old female with severe calcific aortic stenosis, a calcified mitral valve, premature aging, and a family history of similar symptoms. Due to the uncertainty of in silico predictions for this variant, an assessment of nuclear morphology was performed using the immunocytochemistry of stable cell lines to indicate whether the p.(Glu2Lys) had a similar pathogenic mechanism as a previously described pathogenic variant associated with LCPS, p.Asp300Gly. Indirect immunofluorescence analysis of nuclei from stable cell lines showed abnormal morphology, including lobulation and occasional ringed nuclei. Relative to the controls, p.Glu2Lys and p.Asp300Gly nuclei had significantly (p < 0.001) smaller average nuclear areas than controls (mean = 0.10 units, SD = 0.06 for p.Glu2Lys; and mean = 0.09 units, SD = 0.05 for p.Asp300Gly versus mean = 0.12, SD = 0.05 for WT). After functional studies and segregation studies, this variant was upgraded to likely pathogenic. In summary, our findings suggest that p.Glu2Lys impacts nuclear morphology in a manner comparable to what was observed in p.Asp300Gly cells, indicating that the variant is the likely cause of the LCPS segregating within this family.

Keywords

• atypical progeroid syndrome
• <i>LMNA</i>
• mitral valve calcification
• nuclear abnormalities
• case report