This study aims to validate the genotype-phenotype relationship between a newly identified candidate mutation in the MLIP gene and a patient’s distal myopathy.

A cohort of 17 patients with rare myopathies were diagnosed in order to identify the faulty genes causative of their disease. Among those, RNA-sequencing from a patient affected with a progressive adult-onset distal myopathy revealed a homozygous stop-gain mutation in the alternatively spliced gene MLIP. MLIP (Muscular LMNA-Interacting Protein) is highly expressed in muscular tissue. Its role hasn’t been completely elucidated yet. However, it is known to be the direct interactant of LMNA (Lamin Type A/C), which has been linked with laminopathies, cardiomyopathies and muscular dystrophies when dysregulated. The mutation is present in exon 5, the NLS sequence and an alternatively spliced exon; suggestive of a mislocalization, a loss of function and isoform sensitive.

Coupling DNA sequencing and RNA sequencing, the analysis of the patient’s omics data led to the identification of the defective MLIP gene. CRISPR/Cas9 genome editing machinery was used in order to reproduce the candidate mutation in a cell line of immortalized human myoblasts.

Differential expression data showed an important downregulation of MLIP and, by a compensatory mechanism, an upregulation of its interactant LMNA. The mutant cell line seems to show slow proliferation. The expansion of the colony will permit the quantitative testing of: its proliferation rate, differentiation aptitude, cellular localization through immunofluorescence and interactome with LMNA, ISL1 and MYOCD.

Furthering our investigation around mutated MLIP with the cellular model, will allow the consolidation of the diagnosis brought to the patient, as well as gather additional functional data for this relatively unknown protein.