Hyponatremia in neuromyelitis optica spectrum disorders: Literature review

Phenotypic Heterogeneity in Patients with Mutations in the Mitochondrial Complex I Assembly Gene NDUFAF5

BACKGROUND

Rare mutations in NADH:ubiquinone oxidoreductase complex assembly factor 5 (NDUFAF5) are linked to Leigh syndrome.

OBJECTIVE

We aimed to describe clinical characteristics and functional findings in a patient cohort with NDUFAF5 mutations.

METHODS

Patients with biallelic NDUFAF5 mutations were recruited from multi-centers in Taiwan. Clinical, laboratory, radiological, and follow-up features were recorded and mitochondrial assays were performed in patients' skin fibroblasts.

RESULTS

Nine patients from seven unrelated pedigrees were enrolled, eight homozygous for c.836 T > G (p.Met279Arg) in NDUFAF5 and one compound heterozygous for p.Met279Arg. Onset age had a bimodal distribution. The early-onset group (age <3 years) presented with psychomotor delay, seizure, respiratory failure, and hyponatremia. The late-onset group (age ≥5 years) presented with normal development, but slowly progressive dystonia. Combing 25 previously described patients, the p.Met279Arg variant was exclusively identified in Chinese ancestry. Compared with other groups, patients with late-onset homozygous p.Met279Arg were older at onset (P = 0.008), had less developmental delay (P = 0.01), less hyponatremia (P = 0.01), and better prognosis with preserved ambulatory function into early adulthood (P = 0.01). Bilateral basal ganglia necrosis was a common radiological feature, but brainstem and spinal cord involvement was more common with early-onset patients (P = 0.02). A modifier gene analysis showed higher concomitant mutation burden in early-versus late-onset p.Met279Arg homozygous cases (P = 0.04), consistent with more impaired mitochondrial function in fibroblasts from an early-onset case than a late-onset patient.

CONCLUSIONS

The p.Met279Arg variant is a common mutation in our population with phenotypic heterogeneity and divergent prognosis based on age at onset. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Electrolyte Disorders in Mitochondrial Cytopathies: A Systematic Review

SIGNIFICANCE STATEMENT

Several recent studies identified mitochondrial mutations in patients with Gitelman or Fanconi syndrome. Mitochondrial cytopathies are generally not considered in the diagnostic workup of patients with electrolyte disorders. In this systematic review, we investigated the presence of electrolyte disorders in patients with mitochondrial cytopathies to determine the relevance of mitochondrial mutation screening in this population. Our analysis demonstrates that electrolyte disorders are commonly reported in mitochondrial cytopathies, often as presenting symptoms. Consequently, more clinical attention should be raised for mitochondrial disease as cause for disturbances in electrolyte homeostasis. Further prospective cohort studies are required to determine the exact prevalence of electrolyte disorders in mitochondrial cytopathies.

BACKGROUND

Electrolyte reabsorption in the kidney has a high energy demand. Proximal and distal tubular epithelial cells have a high mitochondrial density for energy release. Recently, electrolyte disorders have been reported as the primary presentation of some mitochondrial cytopathies. However, the prevalence and the pathophysiology of electrolyte disturbances in mitochondrial disease are unknown. Therefore, we systematically investigated electrolyte disorders in patients with mitochondrial cytopathies.

METHODS

We searched PubMed, Embase, and Google Scholar for articles on genetically confirmed mitochondrial disease in patients for whom at least one electrolyte is reported. Patients with a known second genetic anomaly were excluded. We evaluated 214 case series and reports (362 patients) as well as nine observational studies. Joanna Briggs Institute criteria were used to evaluate the quality of included studies.

RESULTS

Of 362 reported patients, 289 had an electrolyte disorder, with it being the presenting or main symptom in 38 patients. The average number of different electrolyte abnormalities per patient ranged from 2.4 to 1.0, depending on genotype. Patients with mitochondrial DNA structural variants seemed most affected. Reported pathophysiologic mechanisms included renal tubulopathies and hormonal, gastrointestinal, and iatrogenic causes.

CONCLUSIONS

Mitochondrial diseases should be considered in the evaluation of unexplained electrolyte disorders. Furthermore, clinicians should be aware of electrolyte abnormalities in patients with mitochondrial disease.

Associations between neuromyelitis optica spectrum disorder, Sjögren's syndrome, and conditions with electrolyte disturbances

OBJECTIVE

Electrolyte disorders are among the important conditions negatively affecting the disease course of neuromyelitis optica spectrum disorder (NMOSD). Possible mechanisms may include renal tubular acidosis (RTA) accompanying Sjögren's syndrome (SS), syndrome of inappropriate antidiuretic hormone secretion (SIADH), and central diabetes insipidus (DI). Currently, the overlap profiles between these conditions remain uncertain.

METHODS

This cross-sectional study collected data from the nationwide administrative Diagnosis Procedure Combination (DPC) database and evaluated the overlap profiles.

RESULTS

Among the 28,285,908 individuals from 1203 DPC-covered hospitals, 8477 had NMOSD, 174108 had SS, 4977 had RTA, 7640 had SIADH, and 24,789 had central DI. Of those with NMOSD, 986 (12%) had SS. The odds ratio (OR) for a diagnosis of NMOSD in those with SS compared with those without was 21 [95% confidence interval (CI), 20-23]. Overlap between NMOSD and SS was seen both in males (OR, 28 [95% CI, 23-33]) and females (OR, 16 [15-17]) and was more prominent in the younger population. Among patients with SS, the prevalence of RTA was lower in patients with NMOSD compared with those without NMOSD. Patients with NMOSD showed a higher prevalence of SIADH (OR, 11 [7.5-17]; p < 0.0001) and DI (OR, 3.7 [2.4-5.3]; p < 0.0001). Comorbid SS in NMOSD was associated with a higher prevalence of DI.

CONCLUSIONS

Patients with NMOSD are likely to have SS, SIADH, and central DI. RTA in SS does not facilitate the overlap between NMOSD and SS. SS in NMOSD may predispose patients to DI.

Overlap syndrome of anti-aquaporin-4 positive neuromyelitis optica spectrum disorder and systemic lupus erythematosus: A systematic review of individual patient data

BACKGROUND

Neurological involvement can occur in systemic lupus erythematosus (SLE) due to co-existing neuromyelitis optica spectrum disorder (NMOSD). The symptoms can mimic those of neuropsychiatric manifestations of SLE. Pathogenic anti-aquaporin-4 (AQP4) antibodies, commonly found in NMOSD, are responsible for the neuroinflammatory response and secondary demyelinating lesions. These anti-AQP4 antibodies can be the drivers of neuroinflammatory process in SLE patients, which is distinct from the immunopathogenesis seen in traditional neuropsychiatric SLE. The clinical course is often a relapsing one and is managed differently. In this review, we describe and outline the clinical course and outcomes of AQP4+ NMOSD/SLE overlap cases.

METHODS

To investigate the co-existence of SLE with AQP4+NMOSD, we conducted a systematic review of individual patient data from case reports and case series reported in major databases. The study extracted clinic-demographic features, imaging and laboratory profiles, treatment approaches, and outcomes of these patients. Inclusion criteria for the review required patients to have positivity for AQP4 or NMO in the blood and/or cerebrospinal fluid (CSF) and exhibit at least one manifestation of both NMOSD and SLE.

RESULTS

In this overlap between SLE and AQP4+NMOSD, a high female preponderance was observed, with 42 out of 46 patients (91.3%) being female. Nearly half of the NMOSD cases (47.8%) had onset after lupus, with a median of 5 years between the two diagnoses. Hematological manifestations were seen in the majority of patients (63%), as well as longitudinally extensive transverse myelitis (87%), and brainstem involvement on imaging (29.6%). Cerebrospinal fluid analysis showed a dominantly lymphocytic pleocytosis, with oligoclonal bands being reported scarcely. Although cyclophosphamide was the most common steroid sparing agent used for maintenance, robust evidence for both efficacy and safety in AQP4+NMOSD is available for mycophenolate mofetil, azathioprine, and rituximab. The majority of reported cases showed a relapsing course, while one patient had a monophasic course.

CONCLUSION

AQP4+NMOSD in SLE patients is a relapsing and neurologically disabling disorder that can mimic neuropsychiatric manifestations, frequently occurs after the onset of lupus or may predate, responds to immunosuppressants, and necessitates indefinite treatment.

Pearls & Oy-sters: Syndrome of Inappropriate Antidiuretic Hormone Secretion Presenting as Neuromyelitis Optica Spectrum Disorder Flare

While it was previously believed that neuromyelitis optic spectrum disorder (NMOSD) mostly affected the optic nerves and the spinal cord, it is increasingly recognized that NMOSD can involve any area of the CNS where aquaporin-4 is highly expressed. These other areas can include the hypothalamus and the circumventricular organs that surround the third and fourth ventricles, serving as osmoregulators. The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is one of the most common causes of hyponatremia and has been associated with NMOSD due to these lesions. In this report, we present a case of a patient with known NMOSD, who presented with dizziness, fatigue, and generalized weakness and whose workup revealed hyponatremia in the setting of SIADH and hypothalamic demyelinating lesions. This case illustrates an atypical presentation of NMOSD and the importance of looking for syndromes, such as SIADH. This can guide diagnostic testing, such as getting thin MRI cuts through the hypothalamus and brainstem, as well as advanced management techniques such as immunotherapy.

Neuromyelitis Optica Spectrum Disorder With Hyponatremia as an Initial Presentation: A Case Report

The diagnosis of neuromyelitis optica spectrum disorder (NMOSD) is easily missed or delayed because of its multiple clinical features, especially at initial presentation. Hyponatremia is an infrequent complication of NMOSD and can present as an initial sign. Hyponatremia in a patient with NMOSD might be caused by autoimmune-related antibodies that attack the hypothalamus, causing inappropriate antidiuretic hormone secretion. Awareness of this pathophysiologic mechanism will help clinicians in the early diagnosis of NMOSD. We report a case of NMOSD with hyponatremia as the initial presentation.

Psychiatric symptoms as initial manifestation in neuromyelitis optica spectrum disorder without cortical lesions: A report of two cases

Diagnosing neuromyelitis optica spectrum disorder (NMOSD) remains a challenge, especially in patients with atypical presentations. Here, we describe two NMOSD patients who initially presented psychiatric symptoms without cortical lesions. This report expands our understanding of the possible presentations of NMOSD. Knowledge of rare initial symptoms may allow timely diagnosis and early therapeutic intervention, preventing more severe attacks affecting the spinal cord or eyes.

Influence of osmolality on gastrointestinal fluid volume and drug absorption: potential impact on oral salt supplementation

Background

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is the most frequent cause of hyponatremia in patients with cerebrovascular disease, and is often treated with oral salt tablets. However, we have shown that osmolality-dependent variations in gastrointestinal (GI) fluid volume can alter the concentration of a poorly permeable drug in the GI tract, potentially affecting its absorption. Here, we examined the effect of ingestion of hyperosmotic solution (10% NaCl) on drug concentration and absorption in the GI tract.

Methods

The effects of osmolality on luminal fluid volume and drug absorption in rat intestine (jejunum, ileum and colon) were examined by means of an in situ closed loop method using fluorescein isothiocyanate-dextran 4000 (FD-4) and atenolol. In vivo absorption in rats was determined by measuring the plasma concentration after oral administration of the test compounds dissolved in purified water or hyperosmotic solution (10% NaCl).

Results

Administration of hyperosmotic solution directly into the GI tract significantly increased the GI fluid volume, owing to secretion of water into the lumen. After administration in hyperosmotic solution, the luminal concentration of non-permeable FD-4 was significantly lower than the initial dosing concentration, whereas after administration in purified water, the luminal concentration exceeded the initial concentration. The fraction absorbed of atenolol was markedly lower after administration in hyperosmotic solution than after administration in purified water. An in vivo pharmacokinetic study in rats was consistent with these findings.

Conclusions

Administration of hyperosmotic NaCl solution increased GI fluid volume and reduced the plasma level of orally administered atenolol. This may imply that oral salt tablets used to treat hyponatremia in SIADH patients could decrease the intestinal absorption of concomitantly administered drugs, resulting in lower plasma exposure.

Neuromyelitis optica, aquaporin-4 antibodies, and neuroendocrine disorders

Neuromyelitis optica (NMO) is an autoimmune disorder of the central nervous system that preferentially affects the optic nerve and the spinal cord. In around 80% of NMO patients, autoantibodies binding to aquaporin-4 (AQP4) are detected. AQP4-IgG unifies a spectrum of disorders (NMOSD) that include not only optic neuritis, longitudinally extensive transverse myelitis but also syndromes caused by lesion of the diencephalic region and the circumventricular organs (CVOs). The distinctive immunopathological characteristics of NMOSD lesions, occurring in regions where AQP4 is highly expressed, supports a central role for AQP4-IgG in disease pathogenesis. AQP4 expression is concentrated in CVOs and in the hypothalamus, mainly in the dorsal hypothalamic area, dorsomedial hypothalamic nucleus and suprachiasmatic nucleus. Several neuroendocrine disorders caused by inflammatory lesions involving the diencephalic region have been described in patients with NMOSD, including syndrome of inappropriate antidiuresis, sleep disorders, and other endocrinopathies caused by hypothalamic injury. Focus of this chapter is the involvement of hypothalamus and CVOs in AQP4 autoimmunity.

Longitudinal Evaluation of Serum MOG-IgG and AQP4-IgG Antibodies in NMOSD by a Semiquantitative Ratiometric Method

Background and purpose: Immunoadsorption (IA) is an antibody-depleting therapy used to treat neuromyelitis optica spectrum disorder (NMOSD) associated to antiaquaporin 4 (anti-AQP4-IgG) and antimyelin oligodendrocyte glycoprotein (anti-MOG-IgG) serum autoantibodies. Our aim was to evaluate longitudinal changes of serum MOG-IgG and AQP4-IgG antibody titer and to correlate it with the clinical status.

Methods: Autoantibody titer and clinical features of two MOG-IgG+/AQP4-IgG– and two AQP4-IgG+/MOG-IgG– patients with NMOSD were collected at baseline (T0), after 6 IA courses (T1), and then 2 weeks (T2) and 6 months after treatment (T3). A fluorescent ratiometric assay was used for a quantitative detection of MOG and AQP4 antibodies, based on HEK-293 cells transfected with the full-length hMOG fused to GFP or h-AQP4-M23 isoform fused to m-cherry, respectively. We defined the antibody titer as MOG quantitative ratio (MOGqr) and AQP4 quantitative ratio (AQP4qr).

Results: In Case 1, the MOGqr dropped from 0.98 at T0 to 0.14 at T3, and in Case 2, it decreased from 0.96 at T0 to undetectable at T3. In Case3, the AQP4qr remained high: 0.90 at T0 and 0.92 at T3. In Case 4, the AQP4qr decreased from 0.50 at T0 to undetectable at T3. Complete recovery was found in Cases 1, 2, and 4.

Conclusions: Semiquantitative ratiometric method accurately detects even slight variation of MOG-IgG and AQP4-IgG titer, suggesting it may be useful to monitor the antibody titer during the disease course and maintenance immunotherapy.

Novel mutations in the mitochondrial complex I assembly gene NDUFAF5 reveal heterogeneous phenotypes

Primary mitochondrial complex I deficiency is the most common defect of the mitochondrial respiratory chain. It is caused by defects in structural components and assembly factors of this large protein complex. Mutations in the assembly factor NDUFAF5 are rare, with only five families reported to date. This study provides clinical, biochemical, molecular and functional data for four unrelated additional families, and three novel pathogenic variants. Three cases presented in infancy with lactic acidosis and classic Leigh syndrome. One patient, however, has a milder phenotype, with symptoms starting at 27 months and a protracted clinical course with improvement and relapsing episodes. She is homozygous for a previously reported mutation, p.Met279Arg and alive at 19 years with mild neurological involvement, normal lactate but abnormal urine organic acids. We found the same mutation in one of our severely affected patients in compound heterozygosity with a novel p.Lys52Thr mutation. Both patients with p.Met279Arg are of Taiwanese descent and had severe hyponatremia. Our third and fourth patients, both Caucasian, shared a common, newly described, missense mutation p.Lys109Asn which we show induces skipping of exon 3. Both Caucasian patients were compound heterozygotes, one with a previously reported Ashkenazi founder mutation while the other was negative for additional exonic variants. Whole genome sequencing followed by RNA studies revealed a novel deep intronic variant at position c.223-907A>C inducing an exonic splice enhancer. Our report adds significant new information to the mutational spectrum of NDUFAF5, further delineating the phenotypic heterogeneity of this mitochondrial defect.