Novel SLC20A2 variant in a Japanese patient with idiopathic basal ganglia calcification-1 (IBGC1) associated with dopa-responsive parkinsonism

Novel SLC20A2 variant in a Japanese patient with idiopathic basal ganglia calcification-1 (IBGC1) associated with dopa-responsive parkinsonism

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Download PDF Data Report Open access Published: 04 September 2019 Novel SLC20A2 variant in a Japanese patient with idiopathic basal ganglia calcification-1 (IBGC1) associated with


dopa-responsive parkinsonism Yaeko Ichikawa1, Masaki Tanaka2,3, Eriko Kurita1, Masanori Nakajima1, Masaki Tanaka1, Chizuko Oishi1, Jun Goto4, Shoji Tsuji  ORCID:


orcid.org/0000-0001-5602-56862,3,5 & …Atsuro Chiba1 Show authors Human Genome Variation volume 6, Article number: 44 (2019) Cite this article


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Subjects Medical geneticsNeurological disorders Abstract


Idiopathic basal ganglia calcification-1 (IBGC1) is an autosomal dominant disorder characterized by calcification in the basal ganglia, which can manifest a range of neuropsychiatric


symptoms, including parkinsonism. We herein describe a 64-year-old Japanese IBGC1 patient with bilateral basal ganglia calcification carrying a novel SLC20A2 variant (p.Val322Glufs*92). The


patient also presented with dopa-responsive parkinsonism with decreased dopamine transporter (DAT) density in the bilateral striatum and decreased cardiac 123I-meta-iodobenzylguanidine


uptake.

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Idiopathic basal ganglia calcification (IBGC), also known as Fahr disease or primary familial brain calcification (PFBC), is a disorder characterized by bilateral calcifications in the basal


ganglia and other brain regions. Clinical manifestations of IBGC range from asymptomatic to neuropsychiatric symptoms, including dystonia, parkinsonism, ataxia, and cognitive impairment1.


Typically, the inheritance mode of familial IBGC is an autosomal dominant one and to date, four dominant causal genes of familial IBGC have been identified, including SLC20A2 (IBGC1, MIM:


#213600), PDGFRB (IBGC4, MIM: #615007), PDGFB (IBGC5, MIM: #615483), and XPR1 (IBGC6, MIM: #616413)2,3,4,5. Recently, MYORG was reported as an autosomal recessive causal gene for IBGC


(IBGC7, MIM: #618317)6,7. Variants in SLC20A2, encoding the type III sodium-dependent phosphate transporter 2 (PiT-2), are a major cause of IBGC8,9. Herein, we report an IBGC1 patient with a


novel variant in SLC20A2 associated with dopa-responsive parkinsonism.


The patient was a 63-year-old Japanese woman who presented to our hospital with a one-month history of lumbago and unsteady gait. Neurological examination revealed gait disturbance with


stooped posture and short steps, but rigidity, tremor, weakness, and cerebellar symptoms were not observed. Computed tomography (CT) images of her brain revealed marked calcifications in the


bilateral basal ganglia, thalami, and dentate nuclei (Fig. 1a). Laboratory tests showed that serum calcium, phosphate, and intact parathyroid hormone levels were all within the normal


ranges. There was no family history of IBGC or parkinsonism. After written informed consent was obtained, we analyzed all the coding regions of the IBGC causative genes, SLC20A2, PDGFRB, and


PDGFB, by Sanger sequencing as previously reported10. We diagnosed her as IBGC1 based on the identification of a novel heterozygous frameshift variant, p.Val322Glufs*92


(NM_006749.4:c.965_966delTG, exon 8), in SLC20A2 (Fig. 1b). The variant was absent in the following genome databases: dbSNP 151 (https://www.ncbi.nlm.nih.gov/projects/SNP/), Integrative


Japanese Genome Variation Database (http://ijgvd.megabank.tohoku.ac.jp/), Exome Aggregation Consortium database version 0.3.1 (http://exac.broadinstitute.org/), and Human Gene Mutation


Database (HGMD® Professional 2019.1).

Fig. 1: Imaging and sequencing findings of the patient.


a Computed tomographic (CT) images of the patient show calcifications in the bilateral basal ganglia, thalami, and dentate nuclei. b Electropherogram and sequence of SLC20A2 (NM_006749.4)


from the patient’s DNA shows the c.965_966delTG variant. DNA and corresponding amino acid sequences of wild-type and mutant SLC20A2 alleles are also shown. The c.965_966delTG variant causes


a frameshift variant (p.Val322Glufs*92). c Dopamine transporter (DAT) single photon emission CT shows diffusely decreased DAT density in the bilateral striatum. The specific binding ratios


(SBRs) of both striatum were 0.51 (right) and 0.14 (left). d 123I-meta-iodobenzylguanidine (123I-MIBG) myocardial scintigraphy shows decreased cardiac 123I-MIBG uptake with early and delayed


heart to mediastinum (H/M) rates of 1.995 and 1.585, respectively

Full size image


Ten months after her first visit, she was hospitalized because of difficulties in standing up without assistance at the age of 64. She showed severe bradykinesia, postural instability, and


mild symmetric rigidity without tremor. Her Unified Parkinson Disease Rating Scale part III (UPDRS-III) score was 43 of 108 on the ninth hospital day. Her Mini-Mental State Examination score


was 24 of 30, and her Hasegawa dementia scale revised was 22 of 30. Dopamine transporter (DAT) single photon emission CT using 123I-ioflupane showed diffusely decreased DAT density in the


bilateral striatum (Fig. 1c). The specific binding ratios (SBRs) of both striatum were 0.51 (right) and 0.14 (left). Her 123I-meta-iodobenzylguanidine (123I-MIBG) myocardial scintigraphy


revealed reduced cardiac 123I-MIBG uptake with early and delayed heart to mediastinum (H/M) rates of 1.995 and 1.585, respectively (Fig. 1d). Levodopa therapy (200 mg/day) was started on the


14th hospital day and was effective against bradykinesia and postural instability. She was able to walk without assistance in her room. On the 122nd hospital day, she received 600 mg/day of


levodopa, and her UPDRS-III score markedly improved from 43 to 11.


The variants associated with IBGC are located widely in SLC20A2 among the patients with IBGC, and the correlation of genotype and phenotype remains unclear1,9,11.


Parkinsonism is one of the common clinical symptoms of IBGC. Tadic et al. showed that 13% of patients with SLC20A2 or PDGFRB variants presented with parkinsonism1. Another review reported


motor improvement with dopatherapy in five patients with genetically confirmed IBGC12. Genetically confirmed Japanese IBGC1 patients presenting with parkinsonism have also been reported


(Table 1)10,13,14. Among the five variants summarized in Table 1, two variants (c.516+1G>A and c.965_966delTG) are frameshift variants, presumably resulting in loss of function of SLC20A2.


In addition, a decreased level of SLC20A2 protein was described in the case with the missense variant (c.1909A>C, S637R), raising the possibility of unstable mutant protein13. Although the


functional investigations were not reported for the two missense variants (R71H and G90V), loss-of-function variants are considered for the three variants shown in Table 1. Consistent with


previous reports, the majority of variants associated with IBGC are loss-of-function variants8,9, and the present study also suggests that loss-of-function mechanisms are likely involved in


at least of the three variants. The present case demonstrated decreased DAT density in the bilateral striatum and decreased cardiac 123I-MIBG uptake (Fig. 1c, d). The decreased DAT density


in the bilateral striatum suggested presynaptic dopaminergic dysfunction, which was reported in patients with IBGC14,15,16,17. Saito et al. also showed that postsynaptic dopaminergic


dysfunction in the bilateral striatum matched calcified regions16. These findings suggested that basal ganglia calcification might result in dopaminergic dysfunction in IBGC patients. The


three cases with reduced DAT density in the striatum (cases 2, 5, and 7. Table 1) also presented with decreased cardiac 123I-MIBG uptake, which was indistinguishable from that observed in


patients with Lewy body diseases, including idiopathic Parkinson disease (PD)18. Since PD is a relatively common disease in Japan (prevalence of ~150 per 100,000 persons in Japan)19, the


coincidental presence of idiopathic PD and IBGC remains a possibility concerning dopa-responsive parkinsonism of patients with IBGC1. However, it is important to pay attention to patients


with IBGC who show dopa-responsive parkinsonism to provide appropriate treatment. To clarify the etiologies of dopa-responsive parkinsonism occasionally observed in patients with IBGC,


further functional analyses including DAT SPECT and 123I-MIBG myocardial scintigraphy will be required in a larger number of patients with genetically confirmed IBGC.

Table 1 Variants of


SLC20A2 and clinical features of genetically confirmed IBGC1 Japanese patients with parkinsonismFull size table HGV Database


The relevant data from this Data Report are hosted at the Human Genome Variation Database at https://doi.org/10.6084/m9.figshare.hgv.2603


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Acknowledgements


This work was supported by Grant-in-Aid (No. H26-Jitsuyoka [Nanbyo]-Ippan-080) from the Ministry of Health, Labour and Welfare, Japan (S.T.).


Author informationAuthors and Affiliations Department of Neurology, Kyorin University School of Medicine, Tokyo, Japan


Yaeko Ichikawa, Eriko Kurita, Masanori Nakajima, Masaki Tanaka, Chizuko Oishi & Atsuro Chiba


Department of Neurology, The University of Tokyo Hospital, Tokyo, Japan


Masaki Tanaka & Shoji Tsuji


Institute of Medical Genomics, International University of Health and Welfare, Chiba, Japan


Masaki Tanaka & Shoji Tsuji


Department of Neurology, International University of Health and Welfare Mita Hospital, Tokyo, Japan


Jun Goto


Department of Molecular Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan


Shoji Tsuji


AuthorsYaeko IchikawaView author publications You can also search for this author inPubMed Google Scholar


Masaki TanakaView author publications You can also search for this author inPubMed Google Scholar


Eriko KuritaView author publications You can also search for this author inPubMed Google Scholar


Masanori NakajimaView author publications You can also search for this author inPubMed Google Scholar


Masaki TanakaView author publications You can also search for this author inPubMed Google Scholar


Chizuko OishiView author publications You can also search for this author inPubMed Google Scholar


Jun GotoView author publications You can also search for this author inPubMed Google Scholar


Shoji TsujiView author publications You can also search for this author inPubMed Google Scholar


Atsuro ChibaView author publications You can also search for this author inPubMed Google Scholar


Corresponding author Correspondence to Yaeko Ichikawa.

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About this articleCite this article Ichikawa, Y., Tanaka, M., Kurita, E. et al. Novel SLC20A2 variant in a Japanese patient with idiopathic basal ganglia calcification-1 (IBGC1) associated


with dopa-responsive parkinsonism. Hum Genome Var 6, 44 (2019). https://doi.org/10.1038/s41439-019-0073-7


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Received: 01 June 2019


Revised: 18 July 2019


Accepted: 25 July 2019


Published: 04 September 2019


DOI: https://doi.org/10.1038/s41439-019-0073-7


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