Assi, Muhannad

Basak, A. Nazli

Forouhideh, Yalda

Gorges, Martin

Kassubek, Jan

Knehr, Antje

Ludolph, Albert C.

Meitinger, Thomas

Mueller, Kathrin

Pinkhardt, Elmar H.

Ruf, Wolfgang

Schradt, Falk

Seker, Tuncay

Strom, Tim M.

Tunca, Ceren

Uttner, Ingo

Weishaupt, Jochen H.

English

Open Access LMU ( Ludwig-Maximilians-Univ. München)

LETTER TOTHE EDITORA biallelic mutation links MYORG to autosomal-recessive primary familialbrain calcificationYalda Forouhideh,1 Kathrin Müller,1 Wolfgang Ruf,1 Muhannad Assi,1 Tuncay S eker,2Ceren Tunca,3 Antje Knehr,1 Tim M. Strom,4,5,6 Martin Gorges,1 Falk Schradt,1Thomas Meitinger,4,5,6 Albert C. Ludolph,1 Elmar H. Pinkhardt,1 A. Nazlı Bas ak,3Jan Kassubek,1 Ingo Uttner1 and Jochen H. Weishaupt11 Neurology Department, Ulm University, Ulm, Germany2 GENOMIZE, Bogazici University, Technology Transfer Region, Istanbul, Turkey3 Suna and Inan K|raç Foundation, Neurodegeneration Research Laboratory, KUTTAM, Koç University Med School,Istanbul, Turkey4 SyNergy, Munich Cluster for Systems Neurology, Ludwig Maximilians Universität München, Germany5 Institute of Human Genetics, Technische Universität München, München, Germany6 Institute of Human Genetics, Helmholtz Zentrum München, Neuherberg, GermanyCorrespondence to: Jochen H. WeishauptNeurology DepartmentUlm UniversityAlbert-Einstein-Allee 1189081 UlmGermanyE-mail: jochen.weishaupt@uni-ulm.deSir,Primary familial brain calcification (PFBC) is an adult-onset hereditary disease marked by calcium deposits inmultiple parts of the brain and progressive symptoms thatcan include cerebellar and extrapyramidal syndromes, dys-arthria and neuropsychiatric alterations (Fahr’s syndrome)(Fahr, 1931; Nicolas et al., 2013a, b). Heterozygous muta-tions in PDGFB, PDGFRB, XPR1 and SCL20A2 cancause autosomal-dominantly inherited PFBC (Wang et al.,2012; Keller et al., 2013; Nicolas et al., 2013a, b; Legatiet al., 2015), while autosomal-recessively inherited casesremained genetically unexplained. Most recently, however,Yao et al. (2018) have suggested that biallelic mutations inthe gene KIAA1161/MYORG are a recessive cause forPFBC, based on the analysis of six Chinese families.However, an independent confirmation is currently missingand no MYORG-linked PFBC case has been reported fromoutside China. Here, we show complementary data indicat-ing that MYORG is a novel PFBC disease gene and providean in-depth phenotype characterization.The index patient (Fig 1; Patient IV.1) is a currently 43-year-old male of Turkish origin who presented to ourdepartment with progressive cerebellar dysarthria, and sub-sequently also gait ataxia, dysphagia and forgetfulnessstarting at the age of 39 years. Moreover, family membersreported personality changes with emotional instability,depressive episodes, and intermittent aggressive behaviour.On neurological exam, mild gait disturbance, a dysmetricfinger-nose-test and brisk deep tendon reflexes on the rightside were noted. Logopedic exam confirmed the severe dis-turbance predominantly of the pharyngeal phase ofdeglutition. Neuropsychological examination consisting ofCorsi-Block Span, Digit Span, Paired Associate WordLearning, Doors-Test, Symbol Digit Modalities Test, andWAIS Picture Arrangement revealed a mild cognitiveimpairment with reduced verbal and non-verbal episodicmemory, verbal primary memory and attention capacity.Cranial CT and cranial MRI including susceptibility-weighted imaging revealed symmetric calcifications (hyper-dense or hypointense, respectively) in the basal gangliadoi:10.1093/brain/awy343 BRAIN 2019: 142; 1–4 | e4Advance Access publication January 12, 2019 The Author(s) (2019). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved.For permissions, please email: journals.permissions@oup.comDownloaded from https://academic.oup.com/brain/article/142/2/e4/5288799 by guest on 11 June 2024(pallidum), red nucleus, posterior thalamus, dentate nucleusextending into the cerebellar hemispheres, and periventricu-lar white matter regions (Fig. 2; Patient IV.1). As observedbefore in PFBC patients (Nicolas et al., 2013a, b), thepatient also presented with occipital cortical calcifications[Fig 2A(4 and 8)]. Hyperintense corticospinal tracts andperiventricular microangiopathy were also observed.Video-oculography documented abnormal oculomotor dys-functions including hypermetric saccadic eye movementswhich are in agreement with cerebellar dysfunction.Electroencephalography was completely unremarkable.Hypoparathyroidism, gangliosidoses (GM1-2), Krabbe’sdisease, Gaucher’s disease, metachromatic leukodystrophy,sialidosis and aminoaciduria were excluded. Furthermore,HIV testing, interferon-gamma release assay and immuno-fixation were negative. CSF analysis showed CSF-specificoligoclonal IgG bands but a normal leucocyte count, pro-tein values and lactate concentration. Ferritin concentra-tions were normal both in CSF and serum.Consequently, the diagnosis of idiopathic Fahr’s syn-drome was initially made, but further work-up of thefamily history suggested a genetic cause: mother andfather of the index patient, who are first-degree cousins(Fig. 1, Subjects III.1 and 2), died at the age of 67 and77 years from ischaemic stroke and esophageal cancer,respectively, without signs of PFBC. However, at the timeof his first presentation in our clinic, both brothers of theindex patient were already known to have brain calcifica-tions resembling those observed in the index patient (Fig. 1and 2; Patients IV.2 and 3).The index patient’s 46-year-old brother (Fig. 1; PatientIV.2) started to develop progressive cerebellar dysarthriaand dysphagia 6 years ago. A cranial MRI study revealedwidespread symmetric calcifications with an identical pat-tern as the index patient [Fig. 2B(1–4)]. At the sametime, family members reported emotional instability, and‘schizophrenia’ was diagnosed according to his brothers.However, despite his consent to perform a genetic analysis,the patient refused further clinical work-up.The second, 49-year-old brother, Patient IV.3 (Fig. 1)developed subtle neurological deficits in the past 2 years.He complains about mild memory problems and slightlyslurred speech. On clinical examination mild cerebellar dys-arthria, slight dysmetria of the upper extremities and ele-vated deep tendon reflexes in the lower extremities wereobserved. Cerebellar saccadic eye movement deficits wereconfirmed by video-oculography. Formal neuropsychologi-cal testing revealed a slightly reduced processing speed.MRI of the brain showed symmetric calcifications resem-bling the findings in his brothers [Fig. 2C(1–4); PatientIV.3]. However, in agreement with the milder clinical man-ifestation compared to his brothers, the calcifications wereless pronounced and spared the occipital cortex [Fig.2C(4)]. Routine laboratory testing was unremarkable.Taking together consanguinity of the parents, diseasemanifestation in at least three siblings but absence of aPFBC syndrome in other generations, an autosomal-reces-sive inheritance was most likely. In line with this assump-tion, targeted testing for known autosomal-dominant PFBCgenes (PDGFB, PDGFRB, XPR1 and SCL20A2) remainednegative. Consequently, we performed whole exomesequencing (WES) of the three brothers to elucidate thecause of disease in this family. Upon informed consent,sequencing, read mapping and variant calling was per-formed on HiSeq2000/2500 systems (Illumina) as described(Freischmidt et al., 2015). Variant filtering for rare (minorallele frequency5 1:100) non-synonymous variants presenthomozygously in all three affected brothers left only onecandidate variant, c.1964A4G (p.Ile655Thr) in MYORG(also known as KIAA1161). As a heterozygous mutationcan misleadingly appear homozygous due to a deletion onthe other chromosome, we used the program ExomeDepthfor the identification of copy number variants. The singlecoding exon of MYORG was sequenced to an average cov-erage of 300 reads. ExomeDepth revealed a copy numberof 2 in all three whole exome sequenced patients, and thusdid not provide evidence for a deletion at the position of thecandidate variant in MYORG. This variant has a low allelefrequency of 2.5  105 (7/279 962 alleles; only heterozy-gote individuals detected) according to GnomAD (http://gnomad.broadinstitute.org/). Also high-throughput sequen-cing of additional 1190 Turkish control individualswithout PFBC revealed only 1 of 2380 alleles with thec.1964A4G/p.Ile655Thr variant (frequency 4.2  104;773 whole genome and 417 whole exome sequencing data-sets; mean coverage at this position = 23 reads).To confirm co-segregation of this mutation with diseasephenotype, we approached the two sisters of the threeaffected male patients. Sanger sequencing showed that theyFigure 1 Pedigree of the PFBC family. The PFBC phenotypeis linked to the homozygous c.1964A4G/p.Ile655Thr mutation inMYORG. The index patient is marked with an arrow; filledsymbols = PFBC phenotype; m/m = homozygous mutation;w/m = heterozygous mutation.e4 | BRAIN 2019: 142; 1–4 Letter to the EditorDownloaded from https://academic.oup.com/brain/article/142/2/e4/5288799 by guest on 11 June 2024Figure 2 Imaging results. Cranial CT scan (A1–A4) and SWI (susceptibility weighted MRI imaging) sequences (A5 to E4) of siblings IV.1 toIV.5 (referring to the pedigree in Fig. 1). In individuals IV.1–IV.4 (A1 to D4) with a homozygous c.1964A4G/p.Ile655Thr mutation in MYORGsymmetric calcifications are observed in the basal ganglia (marked by ‘1’), the posterior thalamus (2), the dentate nucleus (3) extending into thecerebellar peduncles, and the periventricular white matter (4). Moreover, cortical calcifications are observed mainly in the occipital lobe (5) inPatients IV.1, IV.2 and IV.4 (white arrows). Pictures of Subject IV.4 additionally show some motion artefacts due to agitation of the subject, as wellas a meningioma in the left frontal hemisphere (D3). MRI of Subject IV.5 (heterozygous c.1964A4G/p.Ile655Thr MYORG mutation) are normaland lack any signals indicating calcium deposits. ant = anterior; l = left; pos = posterior; r = right.Letter to the Editor BRAIN 2019: 142; 1–4 | e4Downloaded from https://academic.oup.com/brain/article/142/2/e4/5288799 by guest on 11 June 2024carried the p.Ile655Thr MYORG mutation in a homozygous(Fig. 1; Patient IV.4) or heterozygous (Patient IV.5) state.Clinical judgement of the 44-year-old sister Patient IV.4(homozygous mutation) was complicated by the fact thatshe sustained a severe car accident with brain trauma andseveral weeks of coma at the age of 13 years. Moreover, shehas a meningioma in the left frontal lobe (Patient IV.4 in Fig.2; visible in D3), and symptomatic epilepsy for 20 years.Notably, in the years after the car accident, the patient hadregained walking abilities and speech until about 6 yearsago, when she started to continuously deteriorate.Currently, she is conscious but tetraplegic, mutistic, aphagicand fed via a percutaneous gastrostomy. Cranial MRIshowed the known meningioma and a slight midline shift,as well as a global brain atrophy, enlarged ventricles and leftfronto-parietal and temporal cortical defects as sequelae ofthe brain trauma in childhood. However, distinct basal gang-lia, brain stem, white matter, occipital cortex and cerebellumcalcifications were also noted, with a symmetrical patternhighly reminiscent of the findings in her three brothers(Fig. 2, Patient IV.4). The cranial imaging result is thereforefully compatible with her homozygous MYORG mutation,and suggests that development of PFBC has contributed toher clinical worsening starting at the age of 38 years.The second 47-year-old sister carries the MYORG muta-tion only in a heterozygous state (Fig. 1; Patient IV.5). Aspredicted based on an autosomal-recessive mode of inheri-tance, she had a completely normal brain MRI without anycalcium deposits (Fig. 2; Patient IV.5). Apart from a con-genital strabismus, she had no neurological or neuropsy-chological signs or symptoms.The PFBC phenotype in this family is therefore perfectlyco-segregating with the homozygous c.1964A4G/p.Ile655Thr MYORG mutation. In synopsis with themost recent findings by Yao et al. (2018), the resultsdemonstrate that MYORG mutations are the so far onlyknown recessively inherited cause for typical PFBC.Furthermore, we describe the first MYORG-associatedPFBC patients outside China. The point mutation identifiedin this Turkish family has not been found in any of theChinese patients, and is the currently most C-terminalMYORG mutation. It is located in a putative glucosidasedomain of the MYORG protein, and could lead to a loss ofenzymatic activity. Currently, however, direct experimentalproof for enzymatic activity of MYORG is missing andrespective tests are not established yet. Moreover, we pro-vide a detailed phenotyping of MYORG-associated PFBCincluding cranial CT, cranial MRI, neuropsychological test-ing, video-oculography and CSF analysis. The clinical andimaging phenotypes of the patients described here resemblethe cases presented by Yao et al. and are within the knowngeneral spectrum of PFBC/Fahr’s syndrome, which typicallycomprises symptoms related to basal ganglia dysfunction,cerebellar deficits as well as neuropsychological and psy-chiatric manifestations. PFBC should thus be recognizedas a possible organic differential diagnosis for psychoses.Whether the CSF-specific antibody production observed inthe index patient is an incidental finding or reflects anintrathecal immune reaction related to PFBC remains spec-ulative. In this context, it is interesting to note that mostPFBC genes are highly expressed in cells that establish theneuro-vascular unit (astrocytes in the case of MYORG),and respective mutations could impair the blood–brainbarrier with subsequent CNS immune alteration. Finally,considering the autosomal-recessive inheritance, we recom-mend testing for MYORG mutations in PFBC/Fahr’s syn-drome patients without an autosomal-dominant inheritanceor with a negative family history.Data availabilityThe data that support the findings of this study are availablefrom the corresponding author, upon reasonable request.AcknowledgementsWe are indebted to the patients and their families for theirparticipation in this project.FundingThis project was supported by Suna and Inan K|raçFoundation’s NDAL at Koç University TranslationalMedicine Research Center.Competing interestsThe authors report no competing interests.ReferencesFahr T. Idiopathische Verkalkung der Hirngefäße. Zentbl Allg PathAnat 1931; 50: 129–33.Freischmidt A, Wieland T, Richter B, Ruf W, Schaeffer V, Müller K,et al. Haploinsufficiency of TBK1 causes familial ALS and fronto-temporal dementia. Nat Neurosci 2015; 18: 631–36.Keller A, Westenberger A, Sobrido MJ, Garcia-Murias M, DomingoA, Sears RL, et al. Mutations in the gene encoding PDGF-Bcause brain calcifications in humans and mice. Nat Genet 2013;45: 1077–82.Legati A, Giovannini D, Nicolas G, Lopez-Sanchez U, Quintans B,Oliveira JR, et al. Mutations in XPR1 cause primary familialbrain calcification associated with altered phosphate export. NatGenet 2015; 47: 579–81.Nicolas G, Pottier C, Charbonnier C, Guyant-Marechal L, Le Ber I,Pariente J, et al. Phenotypic spectrum of probable and genetically-confirmed idiopathic basal ganglia calcification. Brain 2013a; 136:3395–407.Nicolas G, Pottier C, Maltete D, Coutant S, Rovelet-Lecrux A, LegallicS, et al. Mutation of the PDGFRB gene as a cause of idiopathicbasal ganglia calcification. Neurology 2013b; 80: 181–7.Wang C, Li Y, Shi L, Ren J, Patti M, Wang T, et al. Mutations inSLC20A2 link familial idiopathic basal ganglia calcification withphosphate homeostasis. Nat Genet 2012; 44: 254–6.Yao XP, Cheng X, Wang C, Zhao M, Guo XX, Su HZ, et al. Biallelicmutations in MYORG cause autosomal recessive primary familialbrain calcification. Neuron 2018; 98: 1116–23.e1115.e4 | BRAIN 2019: 142; 1–4 Letter to the EditorDownloaded from https://academic.oup.com/brain/article/142/2/e4/5288799 by guest on 11 June 2024

A biallelic mutation links MYORG to autosomal-recessive primary familial brain calcification

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A biallelic mutation links MYORG to autosomal-recessive primary familial brain calcification

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