MT-ND5 mutation causing exercise intolerance displays intercellular heteroplasmy and rapid shifts between generations

Area of Science:

• Genetics
• Cell Biology
• Mitochondrial Medicine

Background:

• Maternally inherited mitochondrial DNA mutations can cause disease.
• Heteroplasmy, the presence of both mutant and wild-type mitochondrial DNA, complicates inheritance patterns.
• The MT-ND5 mutation m.13271T>C causes exercise intolerance.

Purpose of the Study:

• To investigate the inheritance and cellular segregation of the MT-ND5 mutation m.13271T>C.
• To understand the implications of heteroplasmy and segregation for disease transmission.
• To inform genetic counseling for mitochondrial disorders.

Main Methods:

• Analysis of mutation levels in bulk and subcloned muscle cell cultures.
• Mitochondrial DNA transmission studies across generations.
• Investigation of mutation distribution in patient tissues, placenta, and umbilical cord blood.

Main Results:

• The m.13271T>C mutation showed rapid segregation to homoplasmy in cultured cells.
• Mutation levels expanded from mother to patient, with notable accumulation in skeletal muscle.
• The mutation was absent in the patient's placenta and umbilical cord blood, suggesting germline segregation.
• Evidence suggests intercellular heteroplasmy in the patient's germline.

Conclusions:

• The m.13271T>C mutation undergoes rapid intercellular heteroplasmy, potentially leading to homoplasmy in cultured cells.
• Germline transmission studies indicate intercellular heteroplasmy may be present in the patient's germline.
• Strict segregation of mitochondrial DNA mutations accentuates bottleneck effects and complicates genetic counseling for maternally inherited diseases.