Phenotypic and molecular reanalysis of a cohort of patients with monogenic diabetes reveals a case of partial lipodystrophy due to the A8344G mutation in the mitochondrial DNA

SUMMARY

Familial partial lipodystrophy (FPLD) is a very rare genetic disease characterized by insulin resistance due to a loss of subcutaneous fat from the extremities together with a progressive storage of fat around the face and neck and inside the abdomen. In over 50% of cases, molecular genetic testing reveals pathogenic variants in two nuclear genes, LMNA and PPARG. The case reported here refers to a woman phenotypically diagnosed with FPLD, who presented with diabetes and multiple cervical lipomatosis and in whom no variant had been found in the nuclear genes classically associated with this syndrome that could explain her phenotype. Genetic sequencing using a target panel containing 48 nuclear genes related to monogenic diabetes plus the whole mitochondrial genome revealed the mitochondrial variant m.A8344G in 84.1% heteroplasmy. Following molecular diagnosis, her phenotype was expanded with the recognition of additional clinical characteristics: mild sensorineural hearing loss, proximal myopathy, fatigue, cognitive impairment, sensory ataxia, cardiac abnormalities and, finally, muscle biopsy findings compatible with mitochondrial disease. Therefore, careful and detailed phenotypic and genotypic reanalysis proved crucial in improving molecular diagnosis in FPLD.