Clinicogenetical Variants of Progressive External Ophthalmoplegia - An Especial Review of Non-ophthalmic Manifestations

Neuropathic Pain as Main Manifestation of POLG-Related Disease: A Case Report

Mutations in nuclear-encoded genes that are involved in mitochondrial DNA replication and maintenance (e.g., POLG) have been associated with chronic progressive external ophthalmoplegia (CPEO) phenotype. These nuclear genome mutations may lead to multiple mitochondrial DNA deletions or mitochondrial DNA depletion. On the other hand, primary genetic defects of mitochondrial DNA (such as single large-scale deletion or point mutations) have also been associated with the CPEO phenotype. Chronic progressive external ophthalmoplegia (CPEO) may be a manifestation of specific syndromes that, when clinically recognized, prompt clinicians to investigate specific genetic defects. Thus, CPEO, as part of Kearns Sayre syndrome, suggests the presence of a large-scale deletion of mitochondrial DNA. However, in pure CPEO or CPEO plus phenotypes, it is more difficult to know whether causative genetic defects affect the nuclear or mitochondrial DNA. Here, we present a patient with a long-standing history of CPEO plus phenotype, in whom the sequencing of mitochondrial DNA from skeletal muscle was normal, and no other genetic defect was suspected at first. At the time of our evaluation, the presence of polyneuropathy and neuropathic pain prompted us to investigate nuclear genetic defects and, specifically, mutations in the POLG gene. Thus, the sequencing of the POLG gene revealed p.Thr251Ile and p.Pro587Leu mutations in one allele, and p.Ala467Thr mutation in another allele. Although one would expect that mutations in POLG lead to multiple mitochondrial DNA deletions or depletion (loss of copies), the absence of mitochondrial DNA abnormalities in tissue may be explained by heteroplasmy, a lack or no significant involvement of biopsied tissue, or a sampling bias. So, the absence of secondary mitochondrial DNA alterations should not discourage clinicians from further investigating mutations in nuclear-encoded genes. Lastly, mitochondrial point mutations and single mitochondrial DNA deletions very rarely cause CPEO associated with polyneuropathy and neuropathic pain, and POLG-related disease should be considered in this scenario, instead.

Atheromatosis of the Scalp: A Novel Feature of Chronic Progressive External Ophthalmoplegia Plus Due to a Single Mitochondrial DNA Deletion

Chronic progressive external ophthalmoplegia (CPEO) manifests phenotypically as ptosis with ophthalmoplegia or CPEO-plus, with the affection of muscles or organs other than the extra-ocular eye muscles. Herein, a case of CPEO-plus caused by a single mitochondrial DNA (mtDNA) deletion is represented, along with several previously unreported phenotypic features. The patient is a 76-year-old Caucasian female who had experienced slowly progressive bilateral ptosis since the age of 15, followed by gradual ophthalmoparesis without double vision. Since the age of 56, she had developed mild quadriparesis, depression, easy fatigability, hypersomnia, a facial tic, optic atrophy, cataract, glaucoma, hepatomegaly, hepatic steatosis, cholecystolithiasis, diverticulosis, hyperhidrosis, mild hyper-creatine-kinase-emia, hyperlipidemia, and hyperuricemia. Moreover, she had faced previously unreported manifestations of mitochondrial disorders, psoriasis, and multiple scalp atheromas. The phenotype and a single 5kb mtDNA deletion were employed to diagnose CPEO-plus. This case demonstrates that the phenotypic spectrum of CPEO-plus is broader than expected, that psoriasis and scalp atheromas are unique features of a mitochondrial disorder, and that CPEO progresses to CPEO-plus during the years.