The in cis T251I and P587L POLG1 base changes: Description of a new family and literature review

doi:10.1016/j.nmd.2015.01.004

Neuromuscular Disorders

Volume 25, Issue 4, April 2015, Pages 333-339

https://doi.org/10.1016/j.nmd.2015.01.004 Get rights and content

Highlights

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We report a family that carried the T251I+P587L and the new P116Q mutation in POLG1 gene.
•
We describe a particular spectrum of clinical signs associated with these three mutations.
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We do an extensive revision of literature data about the T251I+P587L mutations.

Abstract

Mutations in the polymerase gamma-1 (POLG1) gene, encoding the catalytic subunit of the mtDNA-specific polymerase-γ, compromise the stability of mitochondrial DNA (mtDNA) and are responsible for numerous clinical presentations as autosomal dominant or recessive progressive external ophthalmoplegia (PEO), sensory ataxia, neuropathy, dysarthria and ophthalmoparesis (SANDO), spinocerebellar ataxia with epilepsy (SCAE) and Alpers syndrome.

POLG1 mutations result in extremely heterogeneous phenotypes which often have overlapping clinical findings, making it difficult to categorize patients into syndromes, and genotype–phenotype correlations are still unclear.

We describe a new family with a particular spectrum of clinical signs, that carried the c.752C>T mutation in exon 3 (T251I) and the c.1760C>T in exon 10 (P587L) in cis. These mutations were associated in the proband and in her brother with the new probably pathogenic mutation c.347C>A in exon 2 (P116Q).

The proband presented a progressive cognitive impairment, mild myopathy, dilated cardiac right atrium and posterior white matter mild signal alteration, while her brother had migraine, mild myopathy, palpebral ptosis and posterior white matter mild signal alteration. Their mother and their sister carried the in cis T251I and the P587L mutations. The first presented neurosensorial hypoacusia, fatigue, heart block and a cerebral arteriovenous malformation nidus, while the latter had borderline intellectual functioning and signs of muscular involvement. Their father, with the P116Q mutation, had diabetes and myopathy.

The complexity of the genotype–phenotype correlations associated with POLG1 mutations is reinforced in this work as evidenced by the presence of different clinic features in patients carrying the same mutations.

Introduction

Disorders of nuclear–mitochondrial intergenomic cross talk are the most common form of mitochondrial disorders (MDs), especially with regard to mutations of the polymerase gamma-1 (POLG1) gene [1], that may account for about 25% of MDs [2]. The POLG1 gene on chromosome 15q25 encodes the α subunit of polymerase γ [3], a nuclear-encoded protein involved in replication and repair of mitochondrial DNA (mtDNA) in the eukaryotic cell [4]. POLG1 mutations have been found in patients with autosomal dominant or recessive progressive external ophthalmoplegia (PEO), often complicated by other clinical signs [5] and in ataxic and hepatocerebral syndromes [2].

However POLG1 mutations are associated with a wide spectrum of clinical symptoms and genotype–phenotype correlations are still unclear, as identical POLG1 mutations can give rise to distinct disease phenotypes, with a wide variation in age of onset, electron transport activities and either recessive or dominant pattern of inheritance [6].

In this work we describe a family with an unusual association of clinical signs, variably distributed between the family members, that carried the c.752C>T mutation in exon 3 (T251I) and the c.1760C>T in exon 10 (P587L) in cis, associated, in two of the siblings, with the new probably pathogenic mutation c.347C>A in exon 2 (P116Q). We report in detail the clinical characteristics and do an extensive revision of literature data about the T251I+P587L mutations.

Our work confirms the complexity of genotype–phenotype correlations of POLG1 mutations.

Section snippets

Case report

We examined 6 members (I-4, II-9, II-10, III-1, III-2, III-3) of an Italian non-consanguineous family, in 5 of whom we identified POLG1 gene mutations. Extensive clinical examinations, that included neurological, ophthalmological and cardiological examinations, hearing tests, EEG, EMG, brain MRI or CT, were carried out. Informed written consent was obtained. The family tree is shown in Fig. 1.

The proband (III-3), an 8 year-old girl, was born at term after an uneventful pregnancy. During

Morphologic and biochemical analysis

Muscle specimens of cases III-3, III-1, II-9 and I-4 were taken from the right biceps and 9 µm serial cross-sections were obtained for histochemical stains according to standard procedures. Immunohistochemical analysis was performed for patient I-4 using the following monoclonal antibodies: anti-mouse Dystrophin (VECTOR), anti-α-Sarcoglycan, anti-β-Sarcoglycan, anti-δ-Sarcoglycan, anti-γ-Sarcoglycan, anti-β-Dystoglycan, anti-Caveolin-3 (SANTA CRUZ Biotechnology), anti-laminin α2 chain (merosin)

Morphologic and biochemical analysis

Muscle biopsy of case III-3, performed at age 3, showed variation in fiber size, mild lipid accumulation, some fibers with reinforcement of subsarcolemmal oxidative enzyme activity and some central nuclei. Muscle biopsy of case III-1 showed variation in fiber size and some central nuclei. Case II-9 disclosed variation in fiber size, central nuclei and rare esterase-positive fibers. Case I-4 revealed variation in fiber size, multiple central nuclei and some esterase-positive fibers.

Discussion

POLG1 gene mutations compromise mtDNA stability and may promote accumulation of mtDNA point mutations, multiple deletions and depletion [5].

Recessive mutations tend to cause mtDNA depletion, are usually present in childhood and cause Alpers syndrome or other phenotypes that include liver failure, while dominant mutations tend to cause adult onset multiple secondary deletions of mtDNA and determine PEO phenotype [2]. Unfortunately, muscle analysis may or may not show mosaic pattern staining of

References (34)

ChinneryP.F. et al.
155th ENMC workshop: polymerase gamma and disorders of mitochondrial DNA synthesis, 21–23 September 2007, Naarden, The Netherlands
Neuromuscul Disord
(2008)
WalkerR.L. et al.
A PAC containing the human mitochondrial DNA polymerase gamma gene (POLG) maps to chromosome 15q25
Genomics
(1997)
RoppP.A. et al.
Cloning and characterization of the human mitochondrial DNA polymerase, DNA polymerase gamma
Genomics
(1996)
FerreiraM. et al.
Relative frequency of known causes of multiple mtDNA deletions: two novel POLG mutations
Neuromuscul Disord
(2011)
ChanS.S. et al.
DNA polymerase gamma and mitochondrial disease: understanding the consequence of POLG mutations
Biochim Biophys Acta
(2009)
ScuderiC. et al.
Severe encephalomyopathy in a patient with homoplasmic A5814G point mutation in mitochondrial tRNACys gene
Neuromuscul Disord
(2007)
HudsonG. et al.
Mitochondrial DNA polymerase-gamma and human disease
Hum Mol Genet
(2006)
FilostoM. et al.
Clinical and genetic heterogeneity in progressive external ophthalmoplegia due to mutations in polymerase gamma
Arch Neurol
(2003)
SanetoR.P. et al.
Polymerase gamma disease through the ages
Dev Disabil Res Rev
(2010)
DiMauroS. et al.
Cytochrome c oxidase deficiency in Leigh syndrome
Ann Neurol
(1987)

RiederM.J. et al.

Automating the identification of DNA variations using quality-based fluorescence re-sequencing: analysis of the human mitochondrial genome

Nucleic Acids Res

(1998)

RamenskyV. et al.

Human non-synonymous SNPs: server and survey

Nucleic Acids Res

(2002)

WongL.J. et al.

Molecular and clinical genetics of mitochondrial diseases due to POLG mutations

Hum Mutat

(2008)

TangS. et al.

Mitochondrial DNA polymerase gamma mutations: an ever expanding molecular and clinical spectrum

J Med Genet

(2011)

FerrariG. et al.

Infantile hepatocerebral syndromes associated with mutations in the mitochondrial DNA polymerase-gammaA

Brain

(2005)

LamanteaE. et al.

Sequence analysis of familial PEO shows additional mutations associated with the 752C→T and 3527C→T changes in the POLG1 gene

Ann Neurol

(2004)

StewartJ.D. et al.

Novel POLG1 mutations associated with neuromuscular and liver phenotypes in adults and children

J Med Genet

(2009)

Cited by (19)

Functional analysis of a novel POLγA mutation associated with a severe perinatal mitochondrial encephalomyopathy
2021, Neuromuscular Disorders
Citation Excerpt :
In Alpers syndrome, which is considered to be the most severe end of the spectrum of POLG-related disease, the onset is almost always after the first months of life [6,8,9, 25-27] and only rarely at birth [7]. The p.Thr251Ile/Pro587Leu double mutant is considered pathogenic and is associated with a wide range of clinical phenotypes [19]. The p.His1134Tyr mutation has not been described previously, but a compound heterozygous missense exchange of the same amino acid to arginine (p.His1134Arg) has been associated with a severe phenotype with onset at birth, early death and mtDNA depletion [25,28].
Mutations in the mitochondrial DNA polymerase gamma catalytic subunit (POLγA) compromise the stability of mitochondrial DNA (mtDNA) by leading to mutations, deletions and depletions in mtDNA. Patients with mutations in POLγA often differ remarkably in disease severity and age of onset. In this work we have studied the functional consequence of POLγA mutations in a patient with an uncommon and a very severe disease phenotype characterized by prenatal onset with intrauterine growth restriction, lactic acidosis from birth, encephalopathy, hepatopathy, myopathy, and early death. Muscle biopsy identified scattered COX-deficient muscle fibers, respiratory chain dysfunction and mtDNA depletion. We identified a novel POLγA mutation (p.His1134Tyr) in trans with the previously identified p.Thr251Ile/Pro587Leu double mutant. Biochemical characterization of the purified recombinant POLγA variants showed that the p.His1134Tyr mutation caused severe polymerase dysfunction. The p.Thr251Ile/Pro587Leu mutation caused reduced polymerase function in conditions of low dNTP concentration that mimic postmitotic tissues. Critically, when p.His1134Tyr and p.Thr251Ile/Pro587Leu were combined under these conditions, mtDNA replication was severely diminished and featured prominent stalling. Our data provide a molecular explanation for the patient´s mtDNA depletion and clinical features, particularly in tissues such as brain and muscle that have low dNTP concentration.
Overview of Atypical Diabetes
2020, Endocrinology and Metabolism Clinics of North America
Headache in mitochondrial disorders
2018, Clinical Neurology and Neurosurgery
Citation Excerpt :
Why POLG1 mutations show intrafamilial phenotypic heterogeneity with regard to headache is unknown [36]. One member of a family may present with migraine whereas the other may present without headache but with an arteriovenous malformation nidus [36]. There are some indications that fasting may trigger the development of migraine [37].
Headache is a prominent feature in mitochondrial disorders (MIDs) but no comprehensive overview is currently available. This review aims at summarising and discussing findings concerning type, frequency, pathogenesis, and treatment of headache in MIDs.
The most frequent headache types in MIDs are migraine and migraine-like headache (MLH). MLH is classified as secondary headache. More rarely, tension-type headache, trigemino-autonomic headache, or different secondary headaches can be found. Migraine or MLH may manifest with or without aura. MLH is frequently associated with an ongoing or previous stroke-like episode (SLE) or a seizure but may also occur independently of other neurological features. MLH may be associated with prolonged aura or visual phenomena after headache. Except for MLH, treatment of headache in MIDs is not at variance from other causes of headache. Beyond the broadly accepted subtype-related headache treatment, diet, cofactors, vitamins, and antioxidants may provide a supplementary benefit. Midazolam, l-arginine, or l-citrulline may be beneficial for MLH. The pathogenesis of headache in MIDs largely remains unsolved. However, since migraine and MLH respond both to triptanes, a shared pathomechanism is likely.
In conclusion, migraine and MLH are the prominent headache types in MIDs. MLH may or may not be associated with current or previous SLEs. MLH is pathophysiologically different from migraine and requires treatment at variance from that of migraine with aura.
Synergistic effects of the in cis T251I and P587L mitochondrial DNA polymerase γ disease mutations
2017, Journal of Biological Chemistry
Citation Excerpt :
This outcome strongly suggests that the presence of other in cis mutations could alter the function of Pol γ for better or worse. Scuderi et al. (19) recently compiled a comprehensive list of clinical phenotypes and genetic characteristics of the approximately 50 cases of T251I + P587L mentioned in the literature. The main clinical presentation is PEO, with or without ptosis, and secondary clinical features include ataxia, myopathy, epilepsy, neuropathy, and hepatic diseases.
Human mitochondrial DNA (mtDNA) polymerase γ (Pol γ) is the only polymerase known to replicate the mitochondrial genome. The Pol γ holoenzyme consists of the p140 catalytic subunit (POLG) and the p55 homodimeric accessory subunit (POLG2), which enhances binding of Pol γ to DNA and promotes processivity of the holoenzyme. Mutations within POLG impede maintenance of mtDNA and cause mitochondrial diseases. Two common POLG mutations usually found in cis in patients primarily with progressive external ophthalmoplegia generate T251I and P587L amino acid substitutions. To determine whether T251I or P587L is the primary pathogenic allele or whether both substitutions are required to cause disease, we overproduced and purified WT, T251I, P587L, and T251I + P587L double variant forms of recombinant Pol γ. Biochemical characterization of these variants revealed impaired DNA binding affinity, reduced thermostability, diminished exonuclease activity, defective catalytic activity, and compromised DNA processivity, even in the presence of the p55 accessory subunit. However, physical association with p55 was unperturbed, suggesting intersubunit affinities similar to WT. Notably, although the single mutants were similarly impaired, a dramatic synergistic effect was found for the double mutant across all parameters. In conclusion, our analyses suggest that individually both T251I and P587L substitutions functionally impair Pol γ, with greater pathogenicity predicted for the single P587L variant. Combining T251I and P587L induces extreme thermal lability and leads to synergistic nucleotide and DNA binding defects, which severely impair catalytic activity and correlate with presentation of disease in patients.
Role of the mitochondrial DNA replication machinery in mitochondrial DNA mutagenesis, aging and age-related diseases
2017, Ageing Research Reviews
Citation Excerpt :
Most of the mutations in Pol γ are associated with arPEO. They are compound heterozygotes and often occur with common Pol γ mutations, such as A467T (Van Goethem et al., 2003a), W748S (Van Goethem et al., 2004), R309L (Lamantea et al., 2002), G848S (Lamantea et al., 2002), R627W (Van Goethem et al., 2003a), N846S (Van Goethem et al., 2003c) or T251I in cis with P587L (Lamantea et al., 2002; Scuderi et al., 2015), to name a few. Patients with arPEO have the same clinical features as with adPEO, but with greater variation in symptoms and time of onset.
As regulators of bioenergetics in the cell and the primary source of endogenous reactive oxygen species (ROS), dysfunctional mitochondria have been implicated for decades in the process of aging and age-related diseases. Mitochondrial DNA (mtDNA) is replicated and repaired by nuclear-encoded mtDNA polymerase γ (Pol γ) and several other associated proteins, which compose the mtDNA replication machinery. Here, we review evidence that errors caused by this replication machinery and failure to repair these mtDNA errors results in mtDNA mutations. Clonal expansion of mtDNA mutations results in mitochondrial dysfunction, such as decreased electron transport chain (ETC) enzyme activity and impaired cellular respiration. We address the literature that mitochondrial dysfunction, in conjunction with altered mitochondrial dynamics, is a major driving force behind aging and age-related diseases. Additionally, interventions to improve mitochondrial function and attenuate the symptoms of aging are examined.
The Y831C Mutation of the POLG Gene in Dementia
2023, Biomedicines

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View full text

The in cis T251I and P587L POLG1 base changes: Description of a new family and literature review

Highlights

Abstract

Introduction

Section snippets

Case report

Morphologic and biochemical analysis

Morphologic and biochemical analysis

Discussion

Neuromuscul Disord

Genomics

Genomics

Neuromuscul Disord

Biochim Biophys Acta

Neuromuscul Disord

Mitochondrial DNA polymerase-gamma and human disease

Hum Mol Genet

Clinical and genetic heterogeneity in progressive external ophthalmoplegia due to mutations in polymerase gamma

Arch Neurol

Polymerase gamma disease through the ages

Dev Disabil Res Rev

Cytochrome c oxidase deficiency in Leigh syndrome

Ann Neurol

Automating the identification of DNA variations using quality-based fluorescence re-sequencing: analysis of the human mitochondrial genome

Nucleic Acids Res

Human non-synonymous SNPs: server and survey

Nucleic Acids Res

Molecular and clinical genetics of mitochondrial diseases due to POLG mutations

Hum Mutat

Mitochondrial DNA polymerase gamma mutations: an ever expanding molecular and clinical spectrum

J Med Genet

Infantile hepatocerebral syndromes associated with mutations in the mitochondrial DNA polymerase-gammaA

Brain

Sequence analysis of familial PEO shows additional mutations associated with the 752C→T and 3527C→T changes in the POLG1 gene

Ann Neurol

Novel POLG1 mutations associated with neuromuscular and liver phenotypes in adults and children

J Med Genet