CLCN2-related leukoencephalopathy with novel compound heterozygous variants followed with magnetic resonance imaging over 17 years: a case report

Abstract

Background

CLCN2-related leukoencephalopathy (CC2L) is a rare autosomal recessive disorder caused by biallelic variants of CLCN2, which encodes chloride channel 2. Although CC2L is associated with distinct radiological features, it presents with a wide range of clinical features.

Case presentation

A 34-year-old woman presented to our hospital with a sudden onset of vertigo with headache. The patient reported intermittent headaches and tingling in both arms since the age of 31 years. On the first visit, the patient was alert and neurologically intact, except for slight hyperreflexia of the limbs without laterality. Head magnetic resonance imaging (MRI) showed high-intensity signals on axial T2-weighted fluid-attenuated inversion recovery and diffusion-weighted images bilaterally in the posterior limbs of the internal capsules, cerebral peduncles, superior and middle cerebellar peduncles, decussation of superior cerebellar peduncles, and central tegmental tract. All the patient’s symptoms were resolved or eased following supportive care. The patient stopped attending our hospital at the age of 46 years. At 51 years of age, the patient revisited our hospital because of the recurrence of vertigo, headache, and nausea. She did not present with any abnormalities by neurological examination. Head MRI showed widespread high-intensity signals similar to those 17 years ago. Genetic testing revealed compound heterozygous variants in CLCN2 (NM_004366.6): a novel variant c.1828 C > T, p.(Arg 610*) from her father and c.61dup, p.(Leu21Profs*27) from her mother. The patient was finally diagnosed with CC2L. She received supportive treatment, which made her symptoms manageable.

Conclusions

This is a detailed report of a patient with adult-onset CC2L who was successfully diagnosed and followed up with head MRI. This report provides new insights into CC2L and highlights its persistent, distinct, and stable characteristics observed in head MRI over one decade and the difficulty in forming a diagnosis without MRI when patients have minimal and common symptoms, such as in the present case.

Background

Symptoms of CLCN2-related leukoencephalopathy (CC2L), a rare disorder associated with biallelic mutations of CLCN2 [1] include ataxia, learning disabilities, headaches, mild visual impairment, and male infertility [2]. CLCN2 encodes chloride channel 2 (ClC-2), a chloride channel in the plasma membrane that regulates brain ions and water homeostasis in humans, and various mutations of CLCN2 have been reported [3]. Decreased ClC-2 function in the plasma membrane of astrocytes and oligodendrocytes causes volume retention, myelinic edema, and vacuolation [4].

CC2L is not associated with any specific neurological findings, and its diagnosis is often made through characteristic findings on brain magnetic resonance imaging (MRI) scans and by establishing a proband by identifying biallelic pathogenic variants in CLCN2 using genetic testing [2]. Previously, MRI of adult patients with CC2L demonstrated restricted diffusion suggesting myelin vacuolation confined to the specified white matter structures(4). Despite the importance of MRI for correctly diagnosing CC2L, the monitoring of changes in MRI findings over a prolonged period (i.e., over a decade) has not been reported in patients with CC2L.

We report the case of an individual with CC2L who exhibited distinct findings on head MRI scans over a decade, while only exhibiting common symptoms including vertigo and headache. The diagnosis of CC2L was confirmed by the presence of compound heterozygous variants of CLCN2, including a novel variant. This case report describes the clinical course and follow-up brain MRI findings of adult-onset CC2L.

Case presentation

A 34-year-old Japanese woman presented to our hospital (the National Center of Neurology and Psychiatry National Center Hospital) with a sudden onset of vertigo with headache. Her headache was mild and self-limiting, and its characteristics were similar to those of tension-type headaches. The patient reported intermittent headaches and tingling in both arms since the age of 31 years. The patient’s vertigo started at the age of 32 years when she tilted her head downward. The patient had a history of developmental dysplasia of the hip and angle closure glaucoma. She reported no family history of neurological disease, including her parents, younger sister, and daughter. Her parents were nonconsanguineous. On the first visit, the patient was alert and neurologically intact, except for slight hyperreflexia of the limbs without laterality. Blood tests revealed no abnormalities. Head MRI revealed high-intensity signals on axial T2-weighted, fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted images (DWIs) bilaterally in the posterior limbs of the internal capsules, cerebral peduncles, decussation of superior cerebellar peduncles and middle cerebellar peduncles (Fig. 1). The patient’s symptoms were resolved or eased following supportive care with oral betahistine mesylate. She stopped attending our hospital at the age of 46 years because her symptoms had ameliorated.

Fig. 1.

Brain MRI of the patient at 34 years of age. A–C; Axial fluid-attenuated inversion recovery images, D–F; diffusion-weighted images. Brain MRI of the patient at the age of 51 years. G–I; Axial fluid-attenuated inversion recovery images, J–L; diffusion-weighted images. Abnormally high signal (arrows) in the middle cerebellar peduncles (A, D, G, J), cerebral peduncles and decussation of the superior cerebellar peduncle (B, E, H, K), and posterior limbs of the internal capsules (C, F, I, L) are shown. The abnormally high signal was largely unchanged over the 17 years, although cerebellar atrophy progressed slightly

At 51 years of age, the patient revisited our hospital because of the recurrence of vertigo, headache, and nausea. She did not present with any abnormalities, including nystagmus, ataxia, and hyperreflexia, on neurological examination. An ophthalmological examination was not performed. Head MRI revealed multiple high-intensity signals of axial T2-weighted FLAIR and DWIs that were similar to those observed during her first hospital visit, except for a slight progression of cerebellar atrophy (Fig. 1).

Given the distinct abnormalities detected in the series of head MRI scans, genetic testing was performed for CLCN2 variants. This analysis was approved by the NCNP Clinical Research Review Committee (No. A2019-125), and written informed consent was obtained from the patient and her parents. Genomic DNA was extracted from peripheral blood samples and analyzed via panel testing, whereby the coding exons and untranslated regions/introns of 25 genes (SOX10, GJC2, POLR3A, POLR3B, TUBB4A, PLP1, SLC16A2, SLC17A5, FAM126A, HSPD1, MBP, DEGS1, PYCR2, RARS1, POLR1C, SLC35A2, CLCN2, SPTAN1, GABRG2, U2AF2, AIMP1, EIF2AK2, EPRS, UBTF, and TMEM106B) were covered by 100 reads or more (Kazusa DNA Research Institute, Chiba, Japan). The sequenced reads were aligned to the GRCh38 reference genome using BWA-mem (version 0.7.17), and read processing and variant calls were performed using GATK (version 4.1.9.0). The panel testing and subsequent Sanger sequencing revealed compound heterozygous variants in CLCN2 (NM_004366.6): c.1828 C > T, p.(Arg 610*) from the patient’s father and c.61dup, p.(Leu21Profs*27) from her mother (Fig. 2). On the basis of these results, the patient was finally diagnosed with CLCN2-related leukoencephalopathy (CC2L). To date, her symptoms have been subtle and stabilized by symptomatic anti-dizziness and pain treatments. Furthermore, no cognitive or behavioral changes have been observed.

Fig. 2.

Electropherogram of the patient and her parents. The patient had a compound heterozygous variant in CLCN2, c.61dupC, p. (Leu21Profs*27) from her mother and c.1828 C > T, p. (Arg 610*) from her father

Discussion and conclusions

This case study describes a patient who had CC2L for over 17 years with common symptoms including vertigo and headache, and who was continuously followed up with head MRI. ClC-2, encoded by CLCN2, is one of nine chloride-transporting proteins in the ClC family, and biallelic variants of CLCN2 were reported to cause CC2L [4]. ClC-2 is highly expressed in the brains of humans and regulates neuronal cell volume and post-synaptic responses to gamma-aminobutyric acid and glycine [5, 6]. Because CC2L is associated with distinct head MRI features, MRI might help guide the accurate diagnosis of CC2L. However, changes in MRI over time among patients with CC2L are unclear.

The current case had adult-onset CC2L and compound heterozygous variants in CLCN2 (NM_004366.6): c.61dup, p.(Leu21Profs*27) in exon 1 and c.1828 C > T, p.(Arg 610*) in exon 16, which have not been reported previously. In the Genome Aggregation Database (gnomAD, v4.0.0) [7], allele frequencies of c.61dup and c.1828 C > T are 0.00001921 and 0.000007445, respectively. Interestingly, the allele frequencies of c.61dup and c.1828 C > T are 0.00209 and 0.000129, respectively, in the 54 K JPN database [8], which suggests that c.61dup is relatively prevalent in the Japanese population. The American College of Medical Genetics and Genomics has recommended that these two variants be classified as likely pathogenic (PVS1, PM2_supporting, PM3) [9]. Patients with CC2L were previously reported to have numerous CLCN2 variants [2, 4, 10, 11]. To the best of our knowledge, among previous studies published in English, only two cases of Japanese patients with CC2L have been reported, both of whom carried the homozygous c.61dup variant [1, 12]. In addition, a 70-year-old Japanese man with CC2L was described in an abstract from the regional conference of the Japanese Society of Neurology (December 2021, in Japanese). He had compound heterozygous variants in CLCN2, including the previously unreported c.983 + 2T > A and c.61dup variants. However, we were unable to acquire the details of this case.

Our case exhibited a relatively mild and stable clinical course of CC2L, which differs markedly from previously reported Japanese cases with CC2L. Variability in phenotypes, particularly regarding the age of onset, has been reported since CC2L was first identified [3]. The clinical symptoms of the patient started in adulthood and to date, have been successfully controlled by supportive care. In addition, our patient had an asymptomatic period that lasted for approximately 5 years. The most common neurological findings in CC2L are mild cerebellar ataxia, which can include action tremor and gait instability following initial normal motor functions [2, 4]. Most CC2L patients demonstrate mild clinical phenotypes with prolonged survival. The highly variable clinical presentation and age of onset in reported cases might be associated with the extent of ClC-2 loss-of-function [4].

Previous reports have suggested no genotype-phenotype correlation in CC2L. For example, patients with the same homozygous nonsense variant p.(Trp570*) showed significant differences in the age of onset and phenotype [3]. One of two Japanese patients with the homozygous c.61dup variant presented with generalized tonic-clonic convulsions at the age of 3 months, which were responsive to antiepileptic drugs and did not recur [1]. Another patient had transient fever, headache, and neck stiffness caused by aseptic meningitis without other neurological abnormalities [12]. The c.61dup variant terminates translation at the N-terminal of CLCN2, which might truncate a major section of ClC-2 [1]. The novel, likely pathogenic, c.1828 C > T, p.(Arg 610*) variant terminates translation at the C-terminal of CNCN2, and the c.2257 C > T, p. (Arg753*) variant, which terminates translation at the C-terminal region, was reported to lead to a loss of function [13]. The current case suggests a possible correlation between genotype and phenotype in CC2L. The compound heterozygous variants in CLCN2, including the c.61dup variant, may be more strongly associated with older age of onset and milder symptoms than its homozygous variants. However, compound heterozygous variants of CC2L are relatively rare, and additional cases are needed to better understand this correlation.

Our patient had a clinical phenotype similar to those in previous reports, yet none of the symptoms were specific to CC2L. Her symptoms were mild, intermittent, and manageable with symptomatic treatment. Therefore, we cannot exclude the possibility that her symptoms were unrelated to CC2L. An accurate diagnosis of CC2L is challenging if it depends solely on clinical features, and its ambiguous symptoms and rarity, the necessity of head MRI, and the critical need for gene testing make it difficult to diagnose. However, a recent report suggested that the phenotypic variation in CC2L is more likely to contribute to a difficult diagnosis than its rarity [3, 4]. The intensive implementation of MRI might reveal a larger number of patients with very mild or even asymptomatic forms of CC2L.

The typical characteristics of CCL2 in our patient observed by head MRI images (abnormal symmetrical high signals at the middle cerebellar peduncles, cerebral peduncles and decussation of the superior cerebellar peduncle, and posterior limbs of the internal capsules of axial T2-weighted, FLAIR, and DWIs) remained largely unchanged over the 17 years following her first hospital visit. A series of head MRI scans showed no changes over time, except for a slight progression of cerebellar atrophy. Why the abnormal findings of MRI, including DWIs, remained stable is unclear. However, it may be related to intramyelinic edema, characterized by distinct brain MRI findings involving specific fiber tracts that pass through the brainstem, which are strongly suggestive of CC2L [4, 14]. The major criteria for this condition are abnormally low-intensity signals on T1-weighted images and abnormally high-intensity signals on T2-weighted images in the posterior limbs of the internal capsules, cerebral peduncles, and middle cerebellar peduncles. These features are compatible with the head MRI findings in the current case. In addition, the central tegmental tracts in the medulla, the middle cerebellar peduncles, and the decussation of the superior cerebellar peduncles in the midbrain showed similar intensity abnormalities, which support a diagnosis of CC2L [2]. Restricted diffusion in some affected structures in patients with CC2L was attributed to intramyelinic edema caused by small vacuoles and extracellular spaces [3]. DWI shows hyperintensity in pathological areas, and restricted diffusion in the ADC maps may vary between patients [14]. Of note, some of these characteristic findings in head MRI have been reported to disappear in follow-up MRI [1]. The history of abnormalities in our patient indicated that these MRI features were stable over a long period. Interestingly, our patient did not develop ataxia or muscle weakness despite the detection of lesions in the T2-weighted, FLAIR, and DWI images over 17 years. These discrepancies between clinical features and radiological images might be related to intramyelinic edema without impaired axonal function [10].

In summary, we presented the case of adult-onset CC2L in a Japanese patient with novel compound heterozygous variants in CLCN2. Long-term changes in MRI in CC2L were studied by multiple MRI scans over a decade. CC2L is a rare disease that can present with common symptoms, such as headache and vertigo, as observed in our patient whose characteristic MRI findings remained stable for over a decade. If prolonged headache or vertigo is reported, head MRI should be considered for differential diagnosis to exclude rare diseases such as CC2L at any stage.

Abbreviations

CC2L

CLCN2-related leukoencephalopathy

ClC-2

Chloride channel 2

DWI

Diffusion-weighted imaging

FLAIR

Fluid-attenuated inversion recovery

MRI

Magnetic resonance imaging

Author contributions

M. O. provided medical outpatient care and drafted the manuscript. H. S. and M. N. conducted genetic testing for CLCN2 variants. N. S. performed imaging and analyzed the results. K. I. supported the genetic testing. M. T. supported and advised the diagnosis and patient care. All authors were involved in the conception and design of the work. All authors revised the manuscript critically for important intellectual content, gave final approval of the version to be published, and agreed to be accountable for all aspects of the work.

Funding

This work was supported in part by grants from an intramural fund from the National Center of Neurology and Psychiatry [6–8] (MT), the Japan Society for the Promotion of Science, Grant-in-Aids for Scientific Research (23K27566) (HS), Japan Agency for Medical Research and Development (AMED; grant numbers: JP23ek01099674 and JP23ek0109637 (HS), JP21wm0425019 (MT)), Ministry of Health, Labour and Welfare, Japan (JPMH21FC1015) (KI), Ministry of Health, Labour and Welfare Research on rare and intractable diseases (JPMH23FC1010) (HS), and Takeda Science Foundation Specific Research Grants (HS).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

The patient provided informed consent to participate.

Consent for publication

Written consent was obtained from the patient for publication of this case report. A copy of the written consent is available for review by the Editor of this journal.

Competing interests

The authors declare no competing interests.