Modifying Factors in Striated Muscle Laminopathies

Condition(s) studied

Investigational drug(s) / intervention(s)

Skin Biopsy: The skin biopsy is performed in the consultation outclinic room. A local anaesthetic (anaesthetic patch to be applied to the skin) is required for this procedure. The skin biopsy is usually performed on the front of the forearm (but can be performed on the arm, thigh or leg). After disinfection, a fragment of 3 to 4 mm in diameter is removed with a biopsy-punch (single-use device). If necessary, a suture can be placed. Otherwise, the wound is covered with Steristrip and a sterile dressing. The skin sample, intended for a fibroblast culture, will be placed in a flask to be kept at room temperature. It will be labelled with specific labels and sent to the local biological resource centre.

Muscle biopsy: The muscle biopsy is performed in a sterile room. A local anaesthetic is required for this procedure. After selecting the muscle from which the sample will be taken (usually from the deltoid muscle at the shoulder stump), placing a sterile field and disinfecting, a small incision is made in the skin until the selected muscle is exposed. A bundle of muscle fibres of approximately 1 cm x 0.5 cm is removed. The skin is then sutured and covered with a sterile dressing. The procedure takes about 30 minutes (including patient set-up). The muscle sample will be divided into 2 fragments, one for myoblast culture, the other for frozen tissue. The 2 vials will be labelled with specific labels and then sent to the local biological resource centre

Study summary

Mutations in the LMNA gene, which codes for lamins A and C, proteins of the nuclear lamina, are responsible for a wide spectrum of pathologies, including a group specifically affecting striated skeletal and cardiac muscles, with cardiac involvement being life-threatening. At the skeletal muscle level, a wide phenotypic spectrum has been described, ranging from severe forms of congenital muscular dystrophy to less severe forms of limb-girdle muscular dystrophy. The great clinical variability of striated muscle laminopathies, both inter- and intra-familial, can be observed in the age of onset, severity of signs and progression of muscle and heart involvement. To date, more than 400 LMNA mutations have been associated with striated muscle laminopathies (www.umd.be/LMNA/), highlighting strong clinical and genetic heterogeneity. A few recurrent mutations linked to a difference in severity have been identified. However, these genotype-phenotype relationships and the rare cases of digenism reported do not explain all the clinical variability of laminopathies. Therefore, there are probably other factors of severity than the causative mutation, called "modifier genes".

Identification of such modifier genes has been initiated by studying a large family with significant clinical variability in the age of onset of muscle signs. A segregation analysis within this family identified 2 potential modifier loci. High-throughput sequencing restricted to these 2 regions according to phenotypic subgroups did not led to meaningful results so far. In addition, an international retrospective study of the natural history of early muscle laminopathies has allowed the investigators to highlight a strong inter-family clinical variability in patients carrying recurrent mutations. The investigators thus have strong preliminary data that could allow them to identify modifying genetic factors in a cohort of patients carrying a mutation in the LMNA gene.

In order to identify these factors that modulate the clinical severity of laminopathies, the investigators wish to collect biological material (muscle and/or skin biopsies) from patients carrying a mutation in the LMNA gene. The study of this biological material using multi OMICs technics will allow the investigators to identify and functionally validate the action of these modifying genes.

OMIICs is a set of techniques for characterising biological molecules using high-throughput approaches such as DNA sequencing, RNA sequencing and/or chromatin conformation (ATACseq...), proteins.

Eligibility

Primary outcome measure(s)

• Skeletal muscle severity outcome — 5 years
  Will be a composite scale combining maximal motor acquisitions (sitting, walking, running) and what remains as motor skills with disease course (still running, only walking, only sitting, inability to sit)). In details: * The maximal motor acquisitions (M2A) : no motor acquisitions = 0, only rolling = 1, only sitting = 2, only walking = 3, running = 4. * The remaining motor skills (RMS) with disease course: still running = 3, only walking = 2, only sitting = 1, inability to sit = 0. The composite scale for a given patient will be M2A + RMS.
• Cardiac muscle severity outcome — 5 years
  Will be a composite scale according to left ventricle ejection fraction (normal\>55%, moderate \<55% and \>45%, severe\<45%) and the presence or absence of conduction defects and arrhythmias.
• Protective structural variant outcome — 5 years
  Structural gene variants identified on patient biological materials by Whole Genome Sequencing (WGS), associated with the mild disease severity.
• Protective differential gene expression outcome — 5 years
  differential gene expression identified on patient biological materials by RNA sequencing (RNA-seq) associated with the mild disease severity.
• Protective 3D chromatin conformation outcome — 5 years
  3D conformation of chromatin identified on patient biological materials by Chromatin Immuno-Precipitaiton Sequencing (CHIP Seq) associated with the mild disease severity.
• Aggravating structural variant outcome — 5 years
  Structural gene variants identified on patient biological materials by Whole Genome Sequencing (WGS), associated with the worse disease severity.
• Aggravating differential gene expression outcome — 5 years
  Differential gene expression identified on patient biological materials by RNA sequencing (RNA-seq) associated with the worse disease severity.
• Aggravating 3D chromatin conformation outcome outcome — 5 years
  3D conformation of chromatin identified on patient biological materials by Chromatin Immuno-Precipitaiton Sequencing (CHIP Seq) associated with the worse disease severity.

Trial sites (8)

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