TY - JOUR
AU - Vasiljevic,, Alexandre
AB - Abstract Polymicrogyria is a heterogeneous malformation of cortical development microscopically defined by an excessive folding of the cortical mantle resulting in small gyri with a fused surface. Polymicrogyria is responsible for a wide range of neurological symptoms (e.g. epilepsy, intellectual disability, motor dysfunction). Most cases have a supposed environmental clastic vascular or infectious origin but progress in genomics has revealed new monogenic entities. We report four cases from two independent families sharing a common recognizable lethal syndromic polymicrogyria of autosomal recessive inheritance. Beyond diffuse polymicrogyria detected prenatally, pathological examination revealed a common pattern associating meningeal arterial calcifications, necrotic and calcified areas in basal ganglia, dentato-olivary dysplasia and severe hypoplasia/agenesis of the pyramidal tracts. In all affected cases, exome sequencing showed a pathogenic homozygous nonsense ATP1A2 variant. This resulted in absence of immunodetectable ATP1A2 protein in two brains analysed. ATP1A2 encodes the alpha-2 isoform of the Na+/K+-ATPase, which is highly expressed in brain tissues and has previously been related to familial hemiplegic migraine (MIM#602481) and alternating hemiplegia of childhood (MIM#104290). Through the description of this genetic entity, we emphasize the possibility of dual mode of transmission for disease-causing genes and provide the key neuropathological features that should prompt geneticists to test for mutations in the ATP1A2 gene. polymicrogyria, ATP1A2, brain malformations, meningeal vascular calcifications Introduction Polymicrogyria is a complex cortical malformation accounting for ∼20% of all malformations of cortical development (Leventer et al., 1999). It consists of an excessive folding of the cortical mantle and small gyri with a fused surface. These abnormalities are related to both abnormal late stage neuronal migration and cortical organization. Clinically polymicrogyria is responsible for neurological symptoms such as epilepsy, intellectual disability, motor dysfunction (e.g. spasticity), and pseudobulbar palsy. Polymicrogyria may result from an in utero hypoxic ischaemic injury in the first half of the pregnancy, or may be caused by a cytomegalovirus infection (Crome and France, 1959). Recent advances in genomic technologies have allowed identification of >40 genes responsible for polymicrogyria (Stutterd et al., 2019). These genes are mostly associated with syndromic diseases including peroxisomal disorders (Gressens et al., 2000), tubulinopathies, and alterations of the PIK3-AKT pathway (associated with megalencephaly). We report four cases from two independent families sharing a strikingly similar syndromic lethal polymicrogyria phenotype of autosomal recessive inheritance caused by ATP1A2 homozygous variants. Material and methods Patients Affected cases were identified in two independent families (Patients 1 to 3 from Family A in France; Patient 4 from Family B in the UK). Patient 4 was identified during the literature review process by the French research team. Indeed, a detailed neuropathological analysis of Patient 4 was provided in a broad review on polymicrogyria (Squier and Jansen, 2014) and was strikingly similar to the phenotype identified in the French cases (Patients 2 and 3). The French team contacted the British institution where Patient 4 and his family were managed. Clinical and pathological data were shared by the two independent medical teams. Pathological examination Patients 2–4 underwent a complete autopsy after parental consent according to local ethical laws and standardized procedures. The autopsies were performed by three senior foetopathologists (Patient 2 A.B., Patient 3 A.V. and Patient 4 P.C.) and included external examination, photographs, X-rays, macroscopic and histological examination of all viscera. After extraction, foetal brains were fixed in neutral-buffered formalin and several tissue samples were performed according to the local protocol. Brain samples were paraffin-embedded and cut into 6-µm thick sections. Sections were stained with haematoxylin and eosin, or haematoxylin, phloxine and saffron. The immunoexpression of ATP1A2 was analysed on 4-μm thick paraffin sections of brain tissue in Patients 2 and 3 and compared with brain controls at various stages of development [16, 19, 20, 22, 25, 31 weeks of gestation (WG) and adult brain]. Immunohistochemical analysis was performed using the BenchMark® ULTRA automated immunostainer (Ventana Medical Systems Inc) and an anti-ATP1A2 primary antibody (rabbit polyclonal, AB9094-I, Merck/Sigma-Aldrich, dilution: 1:1000). Immunoreactivity was detected using a Ventana kit including DAB reagent (ultraView Universal DAB Detection Kit). Exome sequencing Both couples consented for exome sequencing of the affected cases and two healthy brothers in Family A. After DNA extraction from frozen material and sonication (Covaris), library preparation was performed with the SureSelect XT Human Exome v5 kit (Agilent Technologies) for Family A and Medexome kit (Roche) for Family B following manufacturers’ instructions. Paired-end 2 × 75 sequencing was performed on a HiSeq2500 and a NextSeq500, respectively (Illumina). Genomic alignment against the hg19/GRCh37 assembly and variant calling were, respectively, done with BWA-MEM v.0.7.12 (Li and Durbin, 2009) and GATK HaplotypeCaller v.3.4 (Broad Institute, Boston, MA, USA) while QC were evaluated using DeCovA (Dimassi et al., 2015). Only highly confident variants were kept for analysis (total depth >9; alternative allele depth >4; no strand bias; mosaicism >10%). Rare variants were considered as having a frequency <1% in gnomAD database. Homozygosity mapping was done from .vcf files using the HomozygosityMapper online tool with default settings. Sanger sequencing was used to confirm variations that would possibly affect protein function. Data availability The raw data supporting the conclusions of this manuscript will be made available by the authors, without undue reservation, to any qualified researcher. ATP1A2 variants have been submitted to ClinVar database (accession number SCV000787761 and SCV000787762, respectively for Families A and B). Results Patients In Family A, three affected siblings were born from consanguineous parents of Algerian descent. The mother suffered from monthly episodes of migraine with tinnitus and nausea, but no other ictal or permanent neurological features were reported in the family. A common cerebral foetal phenotype was encountered during her first, second, and fifth pregnancy. In all cases, ultrasound examination revealed severe microcephaly (between −3 and −4 SD) associated with smooth cortical surface as well as a very rudimentary sylvian fissure and polyhydramnios. T2-weighted foetal MRI (Fig. 1A), performed during the first and second pregnancies, demonstrated abnormal gyration with undulated and mildly thickened cortical ribbon, suggestive of diffuse polymicrogyria. The corpus callosum and posterior fossa were normal. The two first cases (Patients 1 and 2, Table 1), born at 36 and 37 WG, respectively, died after a few hours of life from respiratory distress. For the fifth pregnancy (Patient 3), because of a high probability of severe postnatal outcome, the parents elected for termination of pregnancy at 26 WG after ultrasound examination and prenatal counselling. Table 1 Phenotype summaries of the four patients reported Patient 1 Patient 2 Patient 3 Patient 4 Family A A A B Ethnic origin Algerian Algerian Algerian Pakistani Parental migraine Maternal Maternal Maternal Paternal and maternal Consanguinity + + + + Prenatal ultrasound findings Sex F M M M Microcephaly + + + + Polymicrogyria + + + + Polyhydramnios NK + + + Pregnancy outcome Death after 1 h from respiratory distress Death after 30 min from respiratory distress Termination of pregnancy Termination of pregnancy Term of pregancy (WG) 37 26 35 Prenatal brain MRI findings Abnormal gyration + + + + Other findings Undulated and mildly thickened cortical ribbon Severely dysplastic and abnormal cerebral hemispheres and simple gyral malformation Calcifications - - - - Corpus callosum Normal Normal Normal Normal Posterior fossa Normal Normal Normal Normal Autopsy Microcephaly NA + + + Polymicrogyria NA + + + Meningeal arterial calcifications NA + + + Cerebellum cortex NA Normal Normal Normal Necrotic areas in basal ganglia NA + + + Dentato-olivary dysplasia NA + + + Hypoplasia/agenesis of the pyramidal tracts NA + + + Viral inclusions NA - - - Corpus callosum NA Normal Normal Normal Hippocampus NA Normal Normal Normal Foetal akinesia sequence NA + + + Visceral malformation NA - - Inguinal hernia Extracerebral calcifications NA - - - Patient 1 Patient 2 Patient 3 Patient 4 Family A A A B Ethnic origin Algerian Algerian Algerian Pakistani Parental migraine Maternal Maternal Maternal Paternal and maternal Consanguinity + + + + Prenatal ultrasound findings Sex F M M M Microcephaly + + + + Polymicrogyria + + + + Polyhydramnios NK + + + Pregnancy outcome Death after 1 h from respiratory distress Death after 30 min from respiratory distress Termination of pregnancy Termination of pregnancy Term of pregancy (WG) 37 26 35 Prenatal brain MRI findings Abnormal gyration + + + + Other findings Undulated and mildly thickened cortical ribbon Severely dysplastic and abnormal cerebral hemispheres and simple gyral malformation Calcifications - - - - Corpus callosum Normal Normal Normal Normal Posterior fossa Normal Normal Normal Normal Autopsy Microcephaly NA + + + Polymicrogyria NA + + + Meningeal arterial calcifications NA + + + Cerebellum cortex NA Normal Normal Normal Necrotic areas in basal ganglia NA + + + Dentato-olivary dysplasia NA + + + Hypoplasia/agenesis of the pyramidal tracts NA + + + Viral inclusions NA - - - Corpus callosum NA Normal Normal Normal Hippocampus NA Normal Normal Normal Foetal akinesia sequence NA + + + Visceral malformation NA - - Inguinal hernia Extracerebral calcifications NA - - - Autopsy was refused by the parents for Patient 1. NA = not applicable; NK = not known. Open in new tab Table 1 Phenotype summaries of the four patients reported Patient 1 Patient 2 Patient 3 Patient 4 Family A A A B Ethnic origin Algerian Algerian Algerian Pakistani Parental migraine Maternal Maternal Maternal Paternal and maternal Consanguinity + + + + Prenatal ultrasound findings Sex F M M M Microcephaly + + + + Polymicrogyria + + + + Polyhydramnios NK + + + Pregnancy outcome Death after 1 h from respiratory distress Death after 30 min from respiratory distress Termination of pregnancy Termination of pregnancy Term of pregancy (WG) 37 26 35 Prenatal brain MRI findings Abnormal gyration + + + + Other findings Undulated and mildly thickened cortical ribbon Severely dysplastic and abnormal cerebral hemispheres and simple gyral malformation Calcifications - - - - Corpus callosum Normal Normal Normal Normal Posterior fossa Normal Normal Normal Normal Autopsy Microcephaly NA + + + Polymicrogyria NA + + + Meningeal arterial calcifications NA + + + Cerebellum cortex NA Normal Normal Normal Necrotic areas in basal ganglia NA + + + Dentato-olivary dysplasia NA + + + Hypoplasia/agenesis of the pyramidal tracts NA + + + Viral inclusions NA - - - Corpus callosum NA Normal Normal Normal Hippocampus NA Normal Normal Normal Foetal akinesia sequence NA + + + Visceral malformation NA - - Inguinal hernia Extracerebral calcifications NA - - - Patient 1 Patient 2 Patient 3 Patient 4 Family A A A B Ethnic origin Algerian Algerian Algerian Pakistani Parental migraine Maternal Maternal Maternal Paternal and maternal Consanguinity + + + + Prenatal ultrasound findings Sex F M M M Microcephaly + + + + Polymicrogyria + + + + Polyhydramnios NK + + + Pregnancy outcome Death after 1 h from respiratory distress Death after 30 min from respiratory distress Termination of pregnancy Termination of pregnancy Term of pregancy (WG) 37 26 35 Prenatal brain MRI findings Abnormal gyration + + + + Other findings Undulated and mildly thickened cortical ribbon Severely dysplastic and abnormal cerebral hemispheres and simple gyral malformation Calcifications - - - - Corpus callosum Normal Normal Normal Normal Posterior fossa Normal Normal Normal Normal Autopsy Microcephaly NA + + + Polymicrogyria NA + + + Meningeal arterial calcifications NA + + + Cerebellum cortex NA Normal Normal Normal Necrotic areas in basal ganglia NA + + + Dentato-olivary dysplasia NA + + + Hypoplasia/agenesis of the pyramidal tracts NA + + + Viral inclusions NA - - - Corpus callosum NA Normal Normal Normal Hippocampus NA Normal Normal Normal Foetal akinesia sequence NA + + + Visceral malformation NA - - Inguinal hernia Extracerebral calcifications NA - - - Autopsy was refused by the parents for Patient 1. NA = not applicable; NK = not known. Open in new tab Figure 1 Open in new tabDownload slide Foetal imaging and brain macroscopic features. (A) Coronal T2-weighted foetal MRI demonstrating abnormal gyration with undulated and mildly thickened cortical ribbon (arrows), suggestive of diffuse polymicrogyria (Patient 2 at 29 WG). (B and C) Macroscopically, the brains of Patients 2 (B) and 3 (C) were characterized by an irregular cortical surface with longitudinal striae. Figure 1 Open in new tabDownload slide Foetal imaging and brain macroscopic features. (A) Coronal T2-weighted foetal MRI demonstrating abnormal gyration with undulated and mildly thickened cortical ribbon (arrows), suggestive of diffuse polymicrogyria (Patient 2 at 29 WG). (B and C) Macroscopically, the brains of Patients 2 (B) and 3 (C) were characterized by an irregular cortical surface with longitudinal striae. The 35 WG male foetus previously reported by Squier and Jansen (2014) (Patient 4) had microcephaly, dentato-olivary dysplasia (Fig. 2C and G), meningeal arterial calcifications (Fig. 2K), and calcified areas in deep grey matter, typical of old necrosis events. Both parents had experienced migraine episodes without aura. Figure 2 Open in new tabDownload slide Neuropathological findings in foetuses with ATP1A2 homozygous truncating variants. Haematoxylin and eosin staining, topographic views. (A–D) Transversal bulbar section in Patients 2 (A), 3 (B) and 4 (C). Control transversal bulbar section in a foetus of 27 WG for comparison (D). In the control (D), the inferior olivary nucleus is mature and consists in a convoluted and folded laminar structure. It lies dorsal to the descending pyramidal tract (area surrounded by a yellow dotted line). In the three patients (A–C), the inferior olivary nucleus is coarse and shows a C-shape. The pyramidal tract is absent (yellow arrows). (E–H) Transversal cerebellar section in Patients 2 (E), 3 (F) and 4 (G). Control transversal cerebellar section in a foetus of 27 WG for comparison. In the control (H), the dentate nucleus is mature and consists in a convoluted and folded laminar structure located laterally to the vermis. In the three patients (E–G), the dentate nucleus is ill-defined and presents as a crescent-shaped neuronal mass. (I–K) Leptomeningeal vessels in Patients 2 (I), 3 (J), and 4 (K). Calcifications are observed in the wall of numerous leptomeningeal vessels (black arrows). These calcifications are circumferential for Patients 2 and 4 (I and K) and focal for Patient 4 3(J). For Patients 2 and 4 (I and K), the vascular lumen is reduced by an intimal fibrous thickening. (L-N) In Patients 2 (L), 3 (M), and 4 (N), the neocortex shows abnormal hyperfolded layering consistent with polymicrogyria. Scale bars in A, C and G = 2 mm; B, D and K = 1 mm; E = 5 mm; F and H = 3 mm; I = 200 um; J = 300 μm; L, M and N = 4 mm. Figure 2 Open in new tabDownload slide Neuropathological findings in foetuses with ATP1A2 homozygous truncating variants. Haematoxylin and eosin staining, topographic views. (A–D) Transversal bulbar section in Patients 2 (A), 3 (B) and 4 (C). Control transversal bulbar section in a foetus of 27 WG for comparison (D). In the control (D), the inferior olivary nucleus is mature and consists in a convoluted and folded laminar structure. It lies dorsal to the descending pyramidal tract (area surrounded by a yellow dotted line). In the three patients (A–C), the inferior olivary nucleus is coarse and shows a C-shape. The pyramidal tract is absent (yellow arrows). (E–H) Transversal cerebellar section in Patients 2 (E), 3 (F) and 4 (G). Control transversal cerebellar section in a foetus of 27 WG for comparison. In the control (H), the dentate nucleus is mature and consists in a convoluted and folded laminar structure located laterally to the vermis. In the three patients (E–G), the dentate nucleus is ill-defined and presents as a crescent-shaped neuronal mass. (I–K) Leptomeningeal vessels in Patients 2 (I), 3 (J), and 4 (K). Calcifications are observed in the wall of numerous leptomeningeal vessels (black arrows). These calcifications are circumferential for Patients 2 and 4 (I and K) and focal for Patient 4 3(J). For Patients 2 and 4 (I and K), the vascular lumen is reduced by an intimal fibrous thickening. (L-N) In Patients 2 (L), 3 (M), and 4 (N), the neocortex shows abnormal hyperfolded layering consistent with polymicrogyria. Scale bars in A, C and G = 2 mm; B, D and K = 1 mm; E = 5 mm; F and H = 3 mm; I = 200 um; J = 300 μm; L, M and N = 4 mm. Pathological examination Autopsy of Patients 2 and 3 (Family A) showed a shared complex malformation pattern (Figs 1 and 2). The two foetuses showed microcephaly and features of foetal hypokinesia, including hand contractures and rocker-bottom feet. Macroscopically, the brains were characterized by an irregular cortical surface with longitudinal striae (Fig. 1B and C). Microscopically, the inferior olivary nucleus (Fig. 2A and B) and the cerebellar dentate nucleus (Fig. 2E and F) were dysplastic (dentato-olivary dysplasia) compared with a control (Fig. 2D and H). The bulbar pyramids were absent or severely hypoplastic. Numerous leptomeningeal arteries were calcified in both cases. For Patient 2, calcifications were circumferential with intimal thickening and luminal narrowing (Fig. 2I). Conversely, for Patient 3, calcifications were only focal and intima remained thin (Fig. 2J). Histologically, the abnormal gyral pattern corresponded to diffuse polymicrogyria with foci of leptomeningeal glioneuronal overmigration and linear or irregular calcifications (Fig. 2L and M). Necrotic areas, sometimes calcified, were identified in the basal ganglia, especially in the lentiform nucleus. Perivascular microcalcifications were found in various areas including the cortex, white matter and basal ganglia. The hippocampi were preserved. No extracerebral calcifications were observed. All these features perfectly matched with the neuropathological profile described in Patient 4 by Squier and Jansen (2014). Genetic analysis For Family A, 10× depth of sequencing was achieved for 97.4% of RefSeq coding regions with a mean depth of coverage of 102×. A single truncating variation following the expected autosomal recessive mode of inheritance could be identified, located within the transmembrane part of the cation transporter/ATPase N-terminus domain of ATP1A2 [NM_000702.3: c.295_296dupTC / p.(Ile100Profs*71)]. This duplication was absent from the gnomAD database. It was predicted to lead to a frameshift and to a premature truncated protein. Despite distinct immunopositivity in normal controls (notably arachnoid layer, brain capillaries, astrocytes), no immunostaining was observed in the brains of Patients 2 and 3 confirming absence of the protein (Fig. 3). For Family B, where 99.5% of RefSeq coding regions could be analysed with a mean depth of coverage of 75×, another ATP1A2 homozygous truncating variant [NM_000702.3: c.2869G>T/p.(Glu957*)], also absent from the gnomAD database, was identified. We specifically investigated genes that had been involved in polymicrogyria (Stutterd et al., 2019) and intracerebral calcification disorders (Genomics England Panel App v.1.15) but found no other relevant variant in any of the cases (Supplementary Table 1). Healthy siblings were either heterozygous or not carriers of the variant. Obligate carrier status was confirmed for parents using Sanger sequencing. Figure 3 Open in new tabDownload slide ATP1A2 immunohistochemical analysis. (A and B) ATP1A2 immunoexpression at 25 WG in the cortical plate (A) and in the intermediate zone/future white matter (B). Strong immunopositivity is observed in the capillaries. A weaker positivity is seen in fibrillary processes that are perpendicular to the cortical surface and that may correspond to radial glial cells. In the intermediate zone, some cells show a distinct membranous positivity, probably corresponding to differentiating astrocytes (inset: high magnification view, ×1000). (C and D) ATP1A2 immunoexpression at 31 WG in the cortical plate (C) and the intermediate zone/future white matter (D). The cortical plate shows strong and diffuse fibrillary positivity that has lost its radial arrangement. Capillaries are strongly positive both in the cortex and in the future white matter. In the latter, numerous astrocytes are positive (inset: high magnification view, ×1000). (E and F) Polymicrogyric cortex (E) and intermediate zone/future white matter (F) in Patient 2: absence of immunopositivity (asterisk indicates non-specific staining of microcalcifications). (G and H) Polymicrogyric cortex (G) and intermediate zone/future white matter (H) in Patient 3: absence of immunopositivity. Scale bars in A, C, E, G = 200 μm; B, D, F and H = 50 μm; insets in B and D = 20 μm. Figure 3 Open in new tabDownload slide ATP1A2 immunohistochemical analysis. (A and B) ATP1A2 immunoexpression at 25 WG in the cortical plate (A) and in the intermediate zone/future white matter (B). Strong immunopositivity is observed in the capillaries. A weaker positivity is seen in fibrillary processes that are perpendicular to the cortical surface and that may correspond to radial glial cells. In the intermediate zone, some cells show a distinct membranous positivity, probably corresponding to differentiating astrocytes (inset: high magnification view, ×1000). (C and D) ATP1A2 immunoexpression at 31 WG in the cortical plate (C) and the intermediate zone/future white matter (D). The cortical plate shows strong and diffuse fibrillary positivity that has lost its radial arrangement. Capillaries are strongly positive both in the cortex and in the future white matter. In the latter, numerous astrocytes are positive (inset: high magnification view, ×1000). (E and F) Polymicrogyric cortex (E) and intermediate zone/future white matter (F) in Patient 2: absence of immunopositivity (asterisk indicates non-specific staining of microcalcifications). (G and H) Polymicrogyric cortex (G) and intermediate zone/future white matter (H) in Patient 3: absence of immunopositivity. Scale bars in A, C, E, G = 200 μm; B, D, F and H = 50 μm; insets in B and D = 20 μm. A single run of homozygosity (ROH) present in affected cases of Family A is partly overlapped by a ROH detected in Patient 4 (Family B). Unsurprisingly, this 8.79 Mb region [chr1:152,732,106-161,518,159 (GRCh37)], in 1q21.3q23.3, encompasses ATP1A2 but no other gene previously related to polymicrogyria, consistent with our hypothesis. Discussion In this report, we describe a recognizable form of lethal syndromic polymicrogyria of autosomal recessive inheritance due to ATP1A2 truncating variants. This association was recently reported for the first time by Monteiro et al. (2019) in two families. This is likely to be the most severe clinical presentation among the growing spectrum of phenotypes related to this gene. Indeed, heterozygous missense and truncating variants of ATP1A2 are a common cause of familial hemiplegic migraine (FHM), which is typified by migraine with aura associated with hemiparesis (MIM #602481; FHM2). Three of the four heterozygous carrier parents report migraine episodes. The estimated penetrance for FHM was initially evaluated at 87% (Jurkat-Rott et al., 2004), but this value was potentially overestimated regarding more recent familial reports (de Vries et al., 2007). Interestingly, a new heterozygous variant responsible for hypokalaemic periodic paralysis was reported recently (Sampedro Castañeda et al., 2018) widening, as we do herein, the spectrum of phenotypes related to ATP1A2 reviewed by Friedrich et al. (2016). Overall, to date, more than 80 variants, mostly missense, have been reported as (likely) pathogenic (Friedrich et al., 2016). Many are clustering in the large intracellular loop between membrane-spanning segments 4 and 5. Loss of ATPase function demonstrates haploinsufficiency mechanism (De Fusco et al., 2003). There is no deletion of the locus in the Database of Genomic Variants. ATP1A2 encodes the alpha-2 isoform of the Na+/K+-ATPase which is highly expressed in the brain and skeletal muscle. This pump is responsible for maintaining the Na+/K+ electrochemical gradients across the plasma membrane (Shull and Lingrel, 1987). Atp1a2 knockout mice also present with neurological respiratory dysfunction, leading to death soon after birth, but no polymicrogyria was reported. Pathological examination revealed neuronal cell loss in the amygdala and piriform cortex, with abundant apoptotic neurons but without reported vascular calcifications (Moseley et al., 2003; Ikeda et al., 2004). FHM-related heterozygous missense variants were studied in Drosophila melanogaster showing reduced respiratory activity consistent with a loss of ATPase function (Ashmore et al., 2009). Interestingly, all variants of this publication caused neurological phenotypes with marked vacuolar pathology throughout the brains of the flies. Three cases from two independent families were recently reported as carriers of homozygous loss-of-function ATP1A2 variants (Monteiro et al., 2019). All three cases presented subcutaneous oedema, lack of respiratory drive, microcephaly, dysmorphic features and multiple congenital contractures as part of a foetal akinesia deformation sequence (MIM #2018150). Neuropathology study could only be performed in one case and was briefly described. The main neuropathological features included polymicrogyria, leptomeningeal glioneuronal heterotopia, and calcifications involving cerebral grey and white matter, leptomeninges, and blood vessels. Our cases share similar macroscopic and microscopic features. The detailed neuropathological study of our three patients demonstrates that ATP1A2 homozygous truncating variants are characterized by a distinctive set of lesions that constitutes a recognizable histophenotype. This peculiar neuropathological ‘picture’ includes meningeal arterial calcifications, diffuse polymicrogyria with cortical calcifications, dentato-olivary dysplasia, agenesis of the pyramids, and necrotic areas in basal ganglia. ATP1A2 co-localizes with the glutamate transporters EAAT-1 (excitatory amino acid transporter 1) (SLC1A3), in glial cells and EAAT-2 in the astrocytic plasma membrane (Rose et al., 2009). The Na+/K+ gradient, regulated by ATP1A2, influences the glutamate reuptake ability of EAATs from the synapse into neurons and astrocytes (Illarionava et al., 2014). SLC1A3 mutations have previously been implicated in hemiplegia, episodic ataxia and seizures (Jen et al., 2005), while a severe early-onset developmental epileptic encephalopathy is caused by heterozygous variants of SLC1A2, encoding EAAT-2 (Myers et al., 2016). Thus, glutamate excitotoxicity could be a pathophysiological process common to heterozygous variations of ATP1A2, SLC1A2 and SLC1A3. Such a hypothesis has recently been reinforced by the report of effective NMDA receptor antagonist treatment in a case presenting familial hemiplegic migraine due to an ATP1A2 mutation (Ueda et al., 2018). NMDA metabolism has also previously been implicated in Zellweger syndrome, another form of polymicrogyria, potential differential diagnosis of the phenotype entity described herein. Indeed, Gressens et al. (2000) have been able to demonstrate the importance of NMDA receptors in regulating the rate of neuronal migration using a knockout mouse model of Zellweger syndrome. This knockout model exhibits reduced NMDA neurotransmission. It is known that the glutamatergic system is involved in the modulation of migration of cerebellar granule neurons (Komuro and Rakic, 1993) with inhibitors of NMDA glutamate receptor slowing down the rate of neuronal migration. On the contrary, in newborn hamsters, in vivo excess activation of the NMDA receptors led to disruption of neuronal migration, the first step of polymicrogyria (Marret et al., 1996). Altogether, these experimental data suggest that normal neuronal migration requires a tight control of NMDA receptor activation, potentially disturbed by ATP1A2 homozygous variations. We report herein an additional phenotype related to ATP1A2 dose effect: complete absence of functional copy being lethal with severe cerebral malformations, while the presence of one functional copy leads to neurological disorders with apparently normal brain structure. Such dual genotype/phenotype correlation have been reported previously for other genes: LMNA (Genschel and Schmidt, 2000), GRIN1 (Rossi et al., 2017). Some RELN variants have been shown to cause autosomal-dominant lateral temporal epilepsy (Dazzo et al., 2015), while others were previously found in cases affected with autosomal-recessive lissencephaly with cerebellar hypoplasia. One way to suspect such duality in transmission mode could be to analyse constraint metrics measured on the ExAC dataset (Lek et al., 2016). ATP1A2 scores are, respectively, 0.6002, 0.3998 and 1.3445 × 10−7 for pLi, pRec (intolerance to two loss-of-fucntion variants) and pNull (tolerance to loss-of-function variants). Indeed, for relatively mild phenotypes due to haploinsufficiency, one could hypothesize that cases are still partly present in the dataset thus lowering the intolerance to single loss-of-function variant score (pLi). To test this hypothesis we analysed the constraint scores of the 142 genes related to both autosomal recessive and dominant disorders in OMIM database. Forty of these 142 genes have both pLi and pRec > 0.10 showing a 1.8-fold enrichment over the 3812 OMIM disease-causing genes for which scores could be calculated (P < 0.01, Pearson’s chi-square test). This is in favour of the presence of healthy carriers within the dataset lowering the power of constraint metrics and validates our approach to suspect genes responsible for double transmission modes. In conclusion, ATP1A2 biallelic loss-of-function variants have been recently recognized as a cause of severe polymicrogyria with calcifications (Monteiro et al., 2019). Our report confirms these findings and demonstrates that this disorder is characterized by a distinctive set of neuropathological features including meningeal arterial calcifications, diffuse polymicrogyria with cortical calcifications, dentato-olivary dysplasia, agenesis of the pyramids and necrotic areas in basal ganglia. We also demonstrate the absence of immunodetectable ATP1A2 protein in two affected brains. This is consistent with the involvement of total loss of ATP1A2 in this severe phenotype. The proper recognition of this neuropathological phenotype should prompt the geneticist to consider an analysis of ATP1A2 gene in affected patients. 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TI - A novel lethal recognizable polymicrogyric syndrome caused by ATP1A2 homozygous truncating variants
JF - Brain
DO - 10.1093/brain/awz272
DA - 2019-11-01
UR - https://www.deepdyve.com/lp/oxford-university-press/a-novel-lethal-recognizable-polymicrogyric-syndrome-caused-by-atp1a2-ATORVtLzOQ
SP - 3367
VL - 142
IS - 11
DP - DeepDyve
ER -