Leber hereditary optic neuropathy plus dystonia, and transverse myelitis due to double mutations in MT-ND4 and MT-ND6

Abstract

Leber hereditary optic neuropathy (LHON) typically presents as painless central or centrocecal scotoma and is due to maternally inherited mitochondrial DNA (mtDNA) mutations. Over 95% of LHON cases are caused by one of three mtDNA “common” point mutations; m.3460G>A, m.11778G>A, or m.14484T>C, which are all in genes encoding structural subunits of complex I of the respiratory chain. Intriguing features of LHON include: incomplete penetrance, tissue specificity, and male predominance, indicating that additional genetic or environmental factors are modulating the phenotypic expression of the pathogenic mtDNA mutations. However, since its original description as a purely ophthalmological disorder, LHON has also been linked to multisystemic conditions with variable neurological, cardiac, and skeletal abnormalities. Although double “common” mutations have been reported to cause LHON and LHON-plus, they are extremely rare. Here, we present a patient with an unusual double point mutation (m.11778 G>A and m.14484T>C) with a multisystemic LHON-plus phenotype characterized by: optic neuropathy, ptosis, ataxia, dystonia, dysarthria, and recurrent extensive transverse myelitis.

Introduction

Leber hereditary optic neuropathy (LHON) is one of the most frequent mitochondrial diseases and typically presents in young men with painless loss of central vision in one eye, followed by loss of vision in the second eye within weeks or months [1–2]. Peripapillary telangiectasia are frequently present and can be a clue to the diagnosis. This loss of vision is due to selective vulnerability of retinal ganglion cells in the papillomacular bundle [3]. In vast majority of cases, LHON is a result of one of three mitochondrial DNA (mtDNA) point mutations within genes encoding polypeptide subunits of complex I of the mitochondrial respiratory chain [4–7]. Unlike most mtDNA mutations, which are heteroplasmic (a mixture of both mutant and normal mitochondrial genomes), in the majority of LHON patients, the causative mutation is homoplasmic (100% mutant mtDNA). Although LHON was the first described mitochondrial disease [8–9] and the first to be linked to anmtDNA point mutation [1] many features of the disorder are still unknown. One of the most intriguing features of LHON mutations is incomplete penetrance; all matrilineal members of a LHON pedigree carry the pathogenic mtDNA genotype, yet only some individuals develop the blindness. Other factors thought to modulate the phenotype include: protective effects of estrogen in women, enhanced mitochondrial biogenesis, mtDNA haplotypes, and tobacco smoking and alcohol consumption [10–13]. Although LHON was originally considered to be an isolated ophthalmic disorder [14], extra-ocular neurological manifestations have been reported including: cardiac pre-excitation syndrome, movement disorders, peripheral neuropathy, brainstem and basal ganglia involvement and multiple sclerosis-like syndromes [15–17]. The combination of LHON with extra-ocular manifestation has been described as “LHON-plus syndromes” [18], some of which have linked to mtDNA point mutations other than the three commonly identified in LHON. Interestingly, the LHON-plus mtDNA mutations predominantly occur in mitochondrial respiratory chain complex I subunits and can manifest as isolated optic neuropathy. A neuromyelitis optica (NMO)-like presentation of LHON mtDNA mutations has been described in few patients carrying single mutations [19–20]. Here, we report an atypical combination of LHON-plus with a “NMO spectrum-like” phenotype with ptosis, dysarthria, anddystonia and recurrent episodes of longitudinally extensive transverse myelitis with residual spasticity caused by double pathogenic LHON mtDNA mutations.

Case report

A 36-year-old man of Indian origin, was referred for evaluation of a complex neurological syndrome. He had a history of primary ocular symptoms beginning in childhood with bilateral ptosis and poor vision of the right eye. He relied on his left eye until age 25, when he developed vision loss of the left eye. He was evaluated and treated with vitamin B12 injections in India, but did not improve and was diagnosed with optic neuropathy of unknown etiology. Except for the blindness, he had no other health problems until age 33 years, when he noticed progressive gait impairment and loss of balance, with mild leg weakness and trouble with his speech, for which he was referred to a neurologist. Several months later, he felt right leg and arm weakness associated with pain; imaging showing a large cervical myelopathy/myelitis from C2-C3 to the C7-T1 level in the right central aspect of the cervical cord with subtle mass effect. He was treated with intravenous (IV) steroids for five days, with almost complete improvement after one month. One year after, he had an episode of weakness and pain in his left arm. MRI showed new/more extensive cervical and thoracic cord signal changes with trace enhancement (Fig.1a). He was treated with 5 days of IV steroids. He felt that his left arm function return to 90% of normal after the steroids. After several months, he had a new episode of numbness of left hand and right foot when he was 34 years old; a repeat spinal cord MRI showed new areas of enhancement at the cervical level. He was treated again with IV steroids followed by a taper. By two months later, he had recovered, and a new MRI showed resolution of cord enhancement. He denied history of headaches, seizures or sensory symptoms. There was no family history of neurological disorders or consanguinity. He smoked 2 cigarettes daily as a teenager until age 25 and denied alcohol use.

Figure 1.

a. T2-weighted sagittal MRI images showing extensive abnormal increased signal of the cervical cord from the cervical medullary junction through the lower cervical cord and upper thoracic region (35 y-o). b. Axial section showing preferential involvement of the anterior horns at the upper level of the cervical spine suggesting the “snake eyes sign” (36 y-o) (red arrow) c,d. T2-weighted axial MRI images reveal increased bilaterally signal of the putamen (red arrow), without significant white matter lesions.

Extensive studies were performed. Brain MRI showed bilateral increased T2-signal in the putamen with no white matter involvement (Fig.1c,d). The putaminal lesions remained from the past two years. Orbital MRI showed mild thinning of the prechiasmatic optic nerves without contrast enhancement. Brain magnetic resonance spectroscopy was reportedly normal. Venous lactate and pyruvate were elevated (4mM, with normal values 0.5–2.2 mM, and 0.23 mM, with normal values 0.03–0.15 mM, respectively). Cervical spine MRI at 38 years-old revealed a stable cervical cord abnormality C2-C5, with no enhancement. Axial sections in the upper region of the spinal cord showed preferentially anterior horn involvement (“snake eyes sign”) (Fig.1b). Nerve conduction studies and electromyography were normal. Muscle biopsy showed tubular aggregates, but no ragged-red fibers or cytochrome c oxidase (COX) deficient fibers. Respiratory chain enzyme activities measured spectrophometrically in muscle and fibroblast were normal; including complex I. Serum ceruloplasmin was slightly low 20mg/dL (27–37) with normal copper. The following blood tests were normal or negative: serum NMO/AQP4-IgG antibodies; copper; SSA/SSB antibodies; antinuclear antibodies; acetylcholine binding, blocking, and modulating antibodies; creatine kinase; aldolase; thyroid stimulating hormone; quantitative immunoglobulin; Lyme antibodies; erythrocyte sedimentation rate; C-reactive protein; antineutrophil cytoplasmic antibodies; HIV antibody; rapid plasma regain (RPR), blood smear for acanthocytes and anti-myelin oligodendrocyte glycoprotein (MOG) antibody. Cerebrospinal fluid (CSF) revealed normal white blood count (WBC), elevated lactate (4mM; normal 1.01–2.09) and pyruvate (0.23mM; normal 0.03–0.15), negative oligoclonal bands, normal CSF IgG index/synthesis, herpes simplex virus PCR, VDRL, angiotensin converting enzyme and NMO (anti-aquaporin 4 (AQP4)) IgG. Whole mtDNA sequencing of DNA from the patient’s skin fibroblast and blood revealed two known LHON mutations: m.11778G>A (81% heteroplasmic in skin fibroblast and 76% in blood) in MT-ND4 and m.14484T>C (homoplasmic) in MT-ND6(in both tissues). In contrast, the asymptomatic mother of the proband was positive only for the homoplasmic m.14484T>C (blood). The father was not available for genetic testing.

At age 36, examination showed normal mental status with mild bilateral ptosis with no ophthalmoparesis, mild facial weakness, and severe dysarthria. Visual acuity was severely reduction (20/400) and optic discs were pale. Extra-ocular movements were full with saccadic pursuit and end-lateral gaze-evoked nystagmus. Hearing was normal. Motor examination revealed increased tone, 4+ strength both arms and full strength in the legs with dystonic posturing of the right arm and both legs. Sensory and cerebellar functions were normal. Tendon reflexes were 3+ in the biceps, triceps, and knees, but normal at the ankles. Bilateral Hoffmann and crossed adductors were present but Babinski signs were absent. Gait was mildly wide-based with flexion dystonic posturing at the right wrist and elbow.

Discussion

This 36 year-old gentleman had an unusual LHON-plus presentation, characterized by childhood-onset optic neuropathy and ptosis and subsequent adult-onset limb dystonia, ataxia, speech disturbances, and recurrent episodes of myelitis causing spasticity due to an unusual coexistence of the two common LHON mutations: m.11778G>A and m.14484T>C. This complex phenotype of LHON, dystonia and recurrent transverse myelitis, has not been previously associated with these mutations. The simultaneous occurrence of the m. 11778 G>A and 14484 T>C observed in this patient has been previously reported in few additional families (see Table 1), but all had only ocular manifestations, except for one branch of a LHON pedigree that manifested a fatal infantile encephalopathy [21]. Episodic extensive spinal cord myelitis with optic atrophy has been reported in a patient with dual LHON mutations m.14484T>C and m.4160T>C [22].

Table 1.

Clinical/molecular characteristics of five previously reported cases/families, carrying both m.11778G>A and m.14484T>C mutations.

Author	Opthalmological features	Extraocular manifestations	Biochemical/Functional effects	Heteroplasmic percentage/homoplasmy in blood
Riordan-Eva et al. (1995)[45]	19 yo man. Poor visual recovery. Unaffected relatives.	No	NS	m.11778G>A Homoplasmic in blood m.14484T>C Heteroplasmic (70% in blood)
Brown et al. (2001)	9 yo girl, bilateral visual impairment. No sudden loss. Mild improvement in follow up. Asymptomatic mother	No	Yes	m.11778G>A Heteroplasmic (94% Proband, 31% mother in blood) m.14484T>C Homoplasmic in blood
Howell et al. (2002)	23 yo woman bilateral visual loss at 17, some visual improvement (US family). 42 yo woman onset of recurrent visual loss episodes	Fatal infantile encephalopathy (US family) Sarcoidosis (Australian family)	NS	m.11778G>A Heteroplasmic (65% in blood) m.14484T>C Homoplasmic in blood m.11778G>A Heteroplasmic (71% in blood) m.14484T>C Homoplasmic in blood
Cruz-Bermúdez et al. (2016)	27 yo woman slight bilateral vision loss at age 9. In last few years, clinical deficits have been stable.	No	No	m.11778G>A Homoplasmic in blood m.14484T>C Homoplasmic in blood m.11253T>C Homoplasmic in blood
Catarino et al. (2017)	76 yo woman with subacute vision loss at 75. 2 daughters 46 yo, 36yo Early onset at 6 and 9 years	No	Yes	m.11778G>A Homoplasmic in blood m.14484T>C Heteroplasmic (50% in blood), Daughter (80% m.11778G>A and 60% m.14484T>C in blood)
Our case	32 yo man, childhood-onset poor vision in the right eye. Left eye involvement in adulthood.	Dystonia, dysarthria, mild ataxia, ptosis, recurrent myelitis episodes	NS	m.11778G>A Heteroplasmic (81% fibroblast, 76% blood) m.14484T>C Homoplasmic (fibroblast & blood) Mother m.14484T>C Homoplasmic only (blood)

NS: Not studied.

LHON has been an exception to multiple rules in mtDNA disorders: 1) LHON mutations are typically homoplasmic rather than heteroplasmic; 2) the mutations affect men more frequently than women; and 3) the disorder is typically manifested in only one tissue (optic nerve) rather than multiple organs. While LHON was originally considered an isolated ophthalmic disorder, coexisting neurological disorders and other features such as cardiac conduction abnormalities and kyphosis are relatively frequent [17]. Since Anita Harding et al. first described a rare subset of LHON patients with MS-like features (LHON-MSL) [23], the associations between central nervous system demyelinating lesions and LHON has being confirmed in multiple additional patients [24–27].

The combination of optic neuropathy (ON) and recurrent myelitis in a male patient with recurrent events of ON and longitudinally extensive myelitis occurring weeks or even years apart, is more characteristic of a NMO spectrum disorder than LHON. Therefore, we considered the possibly of two rare independent conditions in our patient, but the presence of bilateral putaminal lesions, absence of NMO-IgG and anti-MOG serum antibodies, and previously reported cases of myelitis and LHON, make the double diagnosis unlikely. Only one report described the combination of LHON and NMO in a patient with a homoplasmic m.11778G>A mutation and AQP4 antibodies [28]. The pathology underlying the spinal cord and brain pathology in patients with LHON and demyelinating features remains unclear. Some cases of LHON with spinal cord involvement have been reported with selective degeneration of posterior columns [29–30]. It is not clear why dorsal tracts are preferentially affected. In our case, anterior cord degeneration was seen in upper segments of the cervical spine mimicking the “snake eyes sign” (Fig.1b). Snake eyes appearance has been described in disorders like ALS, cervical spondylotic amyotrophy, Hirayama disease, ossification of posterior longitudinal ligament, spinal cord infarct and acute flaccid myelitis but not in patients with LHON and spinal cord lesions.

The association of LHON with spastic dystonia (LDYT) is also rare (OMIM#500001) [32], but has been linked to mtDNA mutations in different complex I subunits (MT-ND1, MT-ND3, MT-ND4, and MT-ND6). The clinical characteristics of LDYT are: optic atrophy, spastic dystonia, basal ganglia lesions, and nearly absent complex I activity. The severity of the blindness and progressive generalized dystonia are variable. Childhood and adult-onset have been described and brain images have shown bilateral basal ganglia lucencies in brain computed tomography (CT) scan and occasionally accompanied by pyramidal tract signs and intellectual impairment. In addition to the double mtDNA mutations in the present case, at least five single mutations have been pathogenically associated with LDYT: MT-ND6 m.14459G>A and m.14596T>A, MT-ND4 m.11696A>G, MT-ND1 m.3697G>A and MT-ND3 m.10197G>A [31– 36]. The MT-ND1 m.3697G>A has also presented as mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) [37].

The m.11778G>A or m.14484T>C mutations, either in isolation or combined, have never previously been linked with LDYT and transverse myelitis. We hypothesize that in our patient, the two mutations interact synergistically to cause the severe clinical phenotype. Nevertheless, prior report do not support the synergistic hypothesis. First, the ophthalmological abnormalities in the “two mutation” LHON families previously reported do not appear to differ markedly in terms of the severity of initial vision loss, the eventual recovery in some affected individuals, or the overall penetrance in the pedigrees from classic “one-mutation” LHON pedigrees. Second, a recent study in cybrid cell lines carrying one of the 3 LHON mutations m.11778G>A, m.14484T>C, m.11253T>C, or the double m.11778G>A and m.14484T>C mutations, revealed no differences in mitochondrial function, demonstrating the absence of a synergistic effect in an in vitro model [38]. Third, while a partial reduction in complex I activity has been observed in patients with the m.11778G>A mutation [39], biochemical studies in LHON have produced conflicting results regarding extent of respiratory chain dysfunction, with the reported decrease of complex I activity relative to controls ranging from 0 to 50% for mutation m.11778G>A, 0–65% for m.14484T>C, and more significantly, 60–80%, for m.3460G>A [40]. Functional studies of the mitochondrial defects in lymphoblasts and transmitochondrial cybrid cells with one of three most common LHON mutations m.3460G>A, m.11778G>A orm.14484T>C revealed that the m.14484T>C mutation was associated with a milder biochemical defect than the two other mutations [41–42]. In our patient, respiratory chain enzyme activity measured in muscle and skin fibroblast were normal including, complex I. Therefore, the functional impact of both mutations on complex I activity does not seem to account for the severe phenotype. Spontaneous generation in the oocyte germline or early in embryogenesis may explain the additional heteroplasmic m.11778G>A mutation found in the proband but not the mother.

Another interesting aspect that warrants further investigation, is how a mitochondrial disorder can trigger a neuroinflammatory response, particularly myelitis. A study of the Ndufs4 knockout mouse showed increased transcriptional expression of immune and inflammatory genes coincident with vision impairment suggesting that inflammation is the link between complex I deficiency and vision loss [43]. Moreover, treatment of Ndufs4 KO mice with papaverine, zolpidem, and rapamycin-suppressed inflammation, prevent cell death and protected from visual loss [44]. While response of the myelitis to corticosteroids in our patient suggests an inflammatory etiology, we cannot exclude the possibility that other factors may have contributed in the severity of his phenotype including: gender, tobacco smoking, or other environmental factors in addition to mtDNA haplotype and nuclear DNA modifiers.

In summary, we report a case with an atypical phenotype characterized by LHON-plus and extensive recurrent myelitis episodes in the context of two primaryLHON mutations. This phenotype-genotype combination hasnot previously been reported and should encourage clinicians to screen for common LHON mutations in patients with different combinations of ON and other neurological symptoms. In addition, mitochondrial disorders including LHON should be considered as part of the broad differential presenting with myelitis, even when appearing to be typical demyelination.

Figure 2.