Somatic and germinal mosaicism in a Han Chinese family with laminopathies

Area of Science:

• Genetics
• Molecular Biology
• Neurology

Background:

• Laminopathies are a group of muscle disorders caused by mutations in the LMNA gene.
• These conditions, including limb girdle muscular dystrophy and dilated cardiomyopathy, are typically autosomal dominant.
• Mosaicism, where a mutation is present in some cells but not others, is rarely studied in laminopathies.

Purpose of the Study:

• To investigate a Han Chinese family with suspected laminopathies.
• To identify the genetic cause of the disease in the proband.
• To explore the role of mosaicism in the inheritance of LMNA gene mutations.

Main Methods:

• Genetic analysis to detect mutations in the LMNA gene.
• Reverse-transcription polymerase chain reaction (RT-PCR) to assess LMNA mRNA levels.
• Western blotting to evaluate lamin A/C protein expression in skeletal muscle.

Main Results:

• A novel splice site mutation (c. 1158-3 C>T) in the LMNA gene was identified in the proband.
• The proband's mother exhibited de novo somatic and gonadal mosaicism for this mutation, with normal clinical presentation.
• Reduced LMNA mRNA and lamin A/C protein levels were observed in the proband, likely due to nonsense-mediated mRNA decay.

Conclusions:

• This study underscores the critical role of mosaicism in identifying pathogenic variants in laminopathies.
• The presence of the mutation in the mother's blood sample, despite her normal phenotype, highlights diagnostic challenges.
• Accurate genetic counseling requires careful consideration of potential mosaicism in affected families.