sentence: Experiments performed on mice have demonstrated that homozygous mutations in the proof-reading polymerase γ subunit A ( PolgA ) that lead to accelerated accumulation of subsequent mutations and deletions in mtDNA , cause dramatic decrease in lifespan , premature aging with all the characteristic symptoms ( alopecia , spine kyphosis , osteoporosis ) , as well as loss of subcutaneous fat and reduced fertility [ 11 ] .