Phenotypic and Neuropathological Characterization of Fetal Pyruvate Dehydrogenase Deficiency

Imaging brain glucose metabolism in vivo reveals propionate as a major anaplerotic substrate in pyruvate dehydrogenase deficiency

A vexing problem in mitochondrial medicine is our limited capacity to evaluate the extent of brain disease in vivo. This limitation has hindered our understanding of the mechanisms that underlie the imaging phenotype in the brain of patients with mitochondrial diseases and our capacity to identify new biomarkers and therapeutic targets. Using comprehensive imaging, we analyzed the metabolic network that drives the brain structural and metabolic features of a mouse model of pyruvate dehydrogenase deficiency (PDHD). As the disease progressed in this animal, in vivo brain glucose uptake and glycolysis increased. Propionate served as a major anaplerotic substrate, predominantly metabolized by glial cells. A combination of propionate and a ketogenic diet extended lifespan, improved neuropathology, and ameliorated motor deficits in these animals. Together, intermediary metabolism is quite distinct in the PDHD brain-it plays a key role in the imaging phenotype, and it may uncover new treatments for this condition.

Characteristic Fetal Brain MRI Abnormalities in Pyruvate Dehydrogenase Complex Deficiency

Pyruvate dehydrogenase complex deficiency (PDCD) is a disorder of mitochondrial metabolism that is caused by pathogenic variants in multiple genes, including PDHA1. Typical neonatal brain imaging findings in PDCD have been described, with a focus on malformative features and chronic encephaloclastic changes. However, fetal brain MRI imaging in confirmed PDCD has not been comprehensively described. We sought to demonstrate the prenatal neurological and systemic manifestations of PDCD determined by comprehensive fetal imaging and genomic sequencing. All fetuses with a diagnosis of genetic PDCD who had undergone fetal MRI were included in the study. Medical records, imaging data, and genetic testing results were reviewed and reported descriptively. Ten patients with diagnosis of PDCD were included. Most patients had corpus callosum dysgenesis, abnormal gyration pattern, reduced brain volumes, and periventricular cystic lesions. One patient had associated intraventricular hemorrhages. One patient had a midbrain malformation with aqueductal stenosis and severe hydrocephalus. Fetuses imaged in the second trimester were found to have enlargement of the ganglionic eminences with cystic cavitations, while those imaged in the third trimester had germinolytic cysts. Fetuses with PDCD have similar brain MRI findings to neonates described in the literature, although some of these findings may be subtle early in pregnancy. Additional features, such as cystic cavitations of the ganglionic eminences, are noted in the second trimester in fetuses with PDCD, and these may represent a novel early diagnostic marker for PDCD. Using fetal MRI to identify these radiological hallmarks to inform prenatal diagnosis of PDCD may guide genetic counseling, pregnancy decision-making, and neonatal care planning.

Homozygous MFN2 variants causing severe antenatal encephalopathy with clumped mitochondria

Pathogenic variants in the MFN2 gene are commonly associated with autosomal dominant (CMT2A2A) or recessive (CMT2A2B) Charcot-Marie-Tooth disease, with possible involvement of the CNS. Here, we present a case of severe antenatal encephalopathy with lissencephaly, polymicrogyria and cerebellar atrophy. Whole genome analysis revealed a homozygous deletion c.1717-274_1734 del (NM_014874.4) in the MFN2 gene, leading to exon 16 skipping and in-frame loss of 50 amino acids (p.Gln574_Val624del), removing the proline-rich domain and the transmembrane domain 1 (TM1). MFN2 is a transmembrane GTPase located on the mitochondrial outer membrane that contributes to mitochondrial fusion, shaping large mitochondrial networks within cells. In silico modelling showed that the loss of the TM1 domain resulted in a drastically altered topological insertion of the protein in the mitochondrial outer membrane. Fetus fibroblasts, investigated by fluorescent cell imaging, electron microscopy and time-lapse recording, showed a sharp alteration of the mitochondrial network, with clumped mitochondria and clusters of tethered mitochondria unable to fuse. Multiple deficiencies of respiratory chain complexes with severe impairment of complex I were also evidenced in patient fibroblasts, without involvement of mitochondrial DNA instability. This is the first reported case of a severe developmental defect due to MFN2 deficiency with clumped mitochondria.

Expert Panel Curation of 113 Primary Mitochondrial Disease Genes for the Leigh Syndrome Spectrum

OBJECTIVE

Primary mitochondrial diseases (PMDs) are heterogeneous disorders caused by inherited mitochondrial dysfunction. Classically defined neuropathologically as subacute necrotizing encephalomyelopathy, Leigh syndrome spectrum (LSS) is the most frequent manifestation of PMD in children, but may also present in adults. A major challenge for accurate diagnosis of LSS in the genomic medicine era is establishing gene-disease relationships (GDRs) for this syndrome with >100 monogenic causes across both nuclear and mitochondrial genomes.

METHODS

The Clinical Genome Resource (ClinGen) Mitochondrial Disease Gene Curation Expert Panel (GCEP), comprising 40 international PMD experts, met monthly for 4 years to review GDRs for LSS. The GCEP standardized gene curation for LSS by refining the phenotypic definition, modifying the ClinGen Gene-Disease Clinical Validity Curation Framework to improve interpretation for LSS, and establishing a scoring rubric for LSS.

RESULTS

The GDR with LSS across the nuclear and mitochondrial genomes was classified as definitive for 31 of 114 GDRs curated (27%), moderate for 38 (33%), limited for 43 (38%), and disputed for 2 (2%). Ninety genes were associated with autosomal recessive inheritance, 16 were maternally inherited, 5 were autosomal dominant, and 3 were X-linked.

INTERPRETATION

GDRs for LSS were established for genes across both nuclear and mitochondrial genomes. Establishing these GDRs will allow accurate variant interpretation, expedite genetic diagnosis of LSS, and facilitate precision medicine, multisystem organ surveillance, recurrence risk counseling, reproductive choice, natural history studies, and determination of eligibility for interventional clinical trials. ANN NEUROL 2023;94:696-712.

X-linked pyruvate dehydrogenase complex deficiency due to a novel PDHA1 variant associated with structural brain abnormalities in a fetus

We report a case of pyruvate dehydrogenase E1 alpha subunit deficiency associated with a novel hemizygous PDHA1 variant presenting prenatally as multiple structural brain abnormalities in a male fetus. A healthy Finnish couple was initially referred to the Fetomaternal Medical Center because of suspected fetal choroid plexus cyst at 11 + 2 weeks of pregnancy. At 20 + 0 weeks, multiple abnormalities were observed with ultrasound including narrow thorax, slightly enlarged heart, hypoplastic cerebellum, absent cerebellar vermis and ventriculomegaly. Autopsy and genetic analyses were performed after the termination of pregnancy. The findings of macroscopic examination included cleft palate, abnormally overlapping position of fingers and toes and dysmorphic facial features. Neuropathological examination confirmed the absence of corpus callosum, cerebellar hypoplasia and ventriculomegaly. Nodular neuronal heterotopia was also observed. Trio exome sequencing revealed a novel hemizygous de novo variant c.1144C>T p.(Gln382*) in the PDHA1 gene, classified as likely pathogenic. We suggest that inherited metabolic disorders should be kept in mind as differential diagnoses in fetuses with structural brain abnormalities.

The pyruvate dehydrogenase complex: Life's essential, vulnerable and druggable energy homeostat

Found in all organisms, pyruvate dehydrogenase complexes (PDC) are the keystones of prokaryotic and eukaryotic energy metabolism. In eukaryotic organisms these multi-component megacomplexes provide a crucial mechanistic link between cytoplasmic glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle. As a consequence, PDCs also influence the metabolism of branched chain amino acids, lipids and, ultimately, oxidative phosphorylation (OXPHOS). PDC activity is an essential determinant of the metabolic and bioenergetic flexibility of metazoan organisms in adapting to changes in development, nutrient availability and various stresses that challenge maintenance of homeostasis. This canonical role of the PDC has been extensively probed over the past decades by multidisciplinary investigations into its causal association with diverse physiological and pathological conditions, the latter making the PDC an increasingly viable therapeutic target. Here we review the biology of the remarkable PDC and its emerging importance in the pathobiology and treatment of diverse congenital and acquired disorders of metabolic integration.

Genetic causes of isolated and severe fetal growth restriction in normal chromosomal microarray analysis

OBJECTIVE

To investigate the genetic burden in fetuses with isolated and severe fetal growth restriction (FGR) using Trio whole-exome sequencing (WES) with a normal chromosomal microarray.

METHOD

This retrospective study analyzed WES results of singleton fetuses with isolated and severe FGR, whose estimated fetal weight (EFW) was less than the third percentile by Hadlock formula, in a tertiary center between March 2016 and March 2022. Cases with abnormal chromosomal microarray analysis (CMA) and TORCH results were excluded.

RESULTS

Fifty-one fetuses with isolated and severe FGR and negative CMA results underwent Trio-WES. Of all patients, eight (15.7%) were diagnosed with FGR at its early onset (<32 weeks) and showed pathogenic or likely pathogenic variants involving Nipped-B-like protein gene (NIPBL) (n = 3), fibroblast growth factor receptor 3 (n = 1), pyruvate dehydrogenase E1 subunit alpha 1 (n = 1), collagen, type I, alpha 1 (n = 1), superkiller viralicidic activity 2-like (n = 1), and chloride voltage-gated channel (CLCN5) (n = 1). De novo-generated variants were identified in five fetuses, of which two were novel, including c.6983C>A (p. Thr2328Lys) in NIPBL and c.934-1G>T in CLCN5. Genetic disorders involved Cornelia de Lange syndrome and metabolic and skeletal genetic diseases.

CONCLUSION

The present study indicates that Trio-WES can improve effectivity of prenatal diagnoses for isolated and severe FGR in cases with normal CMA results, aiding prenatal genetic counseling and pregnancy management for FGR fetuses.

Rare metabolic disease mimicking COL4A1/COL4A2 fetal brain phenotype

Pathogenic variants of collagen type IV alpha 1 and 2 (COL4A1/COL4A2) genes cause various phenotypic anomalies, including intracerebral hemorrhage and a wide spectrum of developmental anomalies. Only 20% of fetuses referred for COL4A1/COL4A2 molecular screening (fetuses with a suspected intracerebral hemorrhage) carry a pathogenic variant in these genes, raising questions regarding the causative anomaly in the remaining 80% of these fetuses. We examined, following termination of pregnancy or in-utero fetal death, a series of 113 unrelated fetuses referred for COL4A1/COL4A2 molecular screening, in which targeted sequencing was negative. Using exome sequencing data and a gene-based collapsing test, we searched for enrichment of rare qualifying variants in our fetal cohort in comparison to the Genome Aggregation Database (gnomAD) control cohort (n = 71 702). Qualifying variants in pyruvate dehydrogenase E1 subunit alpha 1 (PDHA1) were overrepresented in our cohort, reaching genome-wide significance (P = 2.11 × 10-7 ). Heterozygous PDHA1 loss-of-function variants were identified in three female fetuses. Among these three cases, we observed microcephaly, ventriculomegaly, germinolytic pseudocysts, agenesis/dysgenesis of the corpus callosum and white-matter anomalies that initially suggested cerebral hypoxic-ischemic and hemorrhagic lesions. However, a careful a-posteriori reanalysis of imaging and postmortem data showed that the observed lesions were also consistent with those observed in fetuses carrying PDHA1 pathogenic variants, strongly suggesting that these two phenotypes may overlap. Exome sequencing should therefore be performed in fetuses referred for COL4A1/COL4A2 molecular screening which are screen-negative, with particular attention paid to the PDHA1 gene. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

Novel imaging findings in pyruvate dehydrogenase complex (PDHc) deficiency-Results from a nationwide population-based study

The vast clinical and radiological spectrum of pyruvate dehydrogenase complex (PDHc) deficiency continues to pose challenges both in diagnostics and disease monitoring. Prompt diagnosis is important to enable early initiation of ketogenic diet. The patients were recruited from an ongoing population-based study in Sweden. All patients with a genetically confirmed diagnosis who had been investigated with an MRI of the brain were included. Repeated investigations were assessed to study the evolution of the MRI changes. Sixty-two MRI investigations had been performed in 34 patients (23 females). The genetic cause was mutations in PDHA1 in 29, PDHX and DLAT in 2 each, and PDHB in 1. The lesions were prenatal developmental in 16, prenatal clastic in 18, and postnatal clastic in 15 individuals. Leigh-like lesions with predominant involvement of globus pallidus were present in 12, while leukoencephalopathy was present in 6 and stroke-like lesions in 3 individuals. A combination of prenatal developmental and clastic lesions was present in 15 individuals. In addition, one male with PDHA1 also had postnatal clastic lesions. The most common lesions found in our study were agenesis or hypoplasia of corpus callosum, ventriculomegaly, or Leigh-like lesions. Furthermore, we describe a broad spectrum of other MRI changes that include leukoencephalopathy and stroke-like lesions. We argue that a novel important clue, suggesting the possibility of PDHc deficiency on MRI scans, is the simultaneous presence of multiple lesions on MRI that have occurred during different phases of brain development.

Metabolic decisions in development and disease-a Keystone Symposia report

There is an increasing appreciation for the role of metabolism in cell signaling and cell decision making. Precise metabolic control is essential in development, as evident by the disorders caused by mutations in metabolic enzymes. The metabolic profile of cells is often cell-type specific, changing as cells differentiate or during tumorigenesis. Recent evidence has shown that changes in metabolism are not merely a consequence of changes in cell state but that metabolites can serve to promote and/or inhibit these changes. Metabolites can link metabolic pathways with cell signaling pathways via several mechanisms, for example, by serving as substrates for protein post-translational modifications, by affecting enzyme activity via allosteric mechanisms, or by altering epigenetic markers. Unraveling the complex interactions governing metabolism, gene expression, and protein activity that ultimately govern a cell's fate will require new tools and interactions across disciplines. On March 24 and 25, 2021, experts in cell metabolism, developmental biology, and human disease met virtually for the Keystone eSymposium, "Metabolic Decisions in Development and Disease." The discussions explored how metabolites impact cellular and developmental decisions in a diverse range of model systems used to investigate normal development, developmental disorders, dietary effects, and cancer-mediated changes in metabolism.

Primary Mitochondrial Disorders of the Pediatric Central Nervous System: Neuroimaging Findings

Primary mitochondrial disorders (PMDs) constitute the most common cause of inborn errors of metabolism in children, and they frequently affect the central nervous system. Neuroimaging findings of PMDs are variable, ranging from unremarkable and nonspecific to florid and highly suggestive. An overview of PMDs, including a synopsis of the basic genetic concepts, main clinical symptoms, and neuropathologic features, is presented. In addition, eight of the most common PMDs that have a characteristic imaging phenotype in children are reviewed in detail. Online supplemental material is available for this article. ^©RSNA, 2020.

Dosage Compensation in Females with X-Linked Metabolic Disorders

Through the use of new genomic and metabolomic technologies, our comprehension of the molecular and biochemical etiologies of genetic disorders is rapidly expanding, and so are insights into their varying phenotypes. Dosage compensation (lyonization) is an epigenetic mechanism that balances the expression of genes on heteromorphic sex chromosomes. Many studies in the literature have suggested a profound influence of this phenomenon on the manifestation of X-linked disorders in females. In this review, we summarize the clinical and genetic findings in female heterozygotic carriers of a pathogenic variant in one of ten selected X-linked genes whose defects result in metabolic disorders.

Fumarase Deficiency: A Case With a New Pathogenic Mutation and a Review of the Literature

Fumarase deficiency (FD) is a rare and severe autosomal disorder, caused by inactivity of the enzyme fumarase, due to biallelic mutations of the fumarase hydratase (FH) gene. Several pathogenic mutations have been published. The article describes an infant with failure to thrive, microcephaly, axial hypotonia, and developmental retardation with increased excretion of fumarate, no activity of fumarase and a homozygous mutation of the FH gene, which was until recently only known as a variant of unknown significance. Carriers of pathogenic mutations in the FH gene are at risk for developing renal cell carcinoma and should therefore be screened. Both parents were healthy carriers of the mutation and had decreased levels of enzyme activity. In addition, the article presents an overview and analysis of all cases of FD reported thus far in the literature.

Developmental brain abnormalities and acute encephalopathy in a patient with myopathy with extrapyramidal signs secondary to pathogenic variants in MICU1

Mitochondria play a variety of roles in the cell, far beyond their widely recognized role in ATP generation. One such role is the regulation and sequestration of calcium, which is done with the help of the mitochondrial calcium uniporter (MCU) and its regulators, MICU1 and MICU2. Genetic variations in MICU1 and MICU2 have been reported to cause myopathy, developmental disability and neurological symptoms typical of mitochondrial disorders. The symptoms of MICU1/2 deficiency have generally been attributed to calcium regulation in the metabolic and biochemical roles of mitochondria. Here, we report a female child with heterozygous MICU1 variants and multiple congenital brain malformations on MRI. Specifically, she shows anterior perisylvian polymicrogyria, dysmorphic basal ganglia, and cerebellar dysplasia in addition to white matter abnormalities. These novel findings suggest that MICU1 is necessary for proper neurodevelopment through a variety of potential mechanisms, including calcium-mediated regulation of the neuronal cytoskeleton, Miro1-MCU complex-mediated mitochondrial movement, or enhancing ATP production. This case provides new insight into the molecular pathogenesis of MCU dysfunction and may represent a novel diagnostic feature of calcium-based mitochondrial disease.

Distinguishing Encephaloclastic Lesions Resulting From Primary or Secondary Pyruvate Dehydrogenase Deficiency From Other Neonatal or Infantile Cavitary Brain Lesions

The central nervous system (CNS) is a highly complex and energy-dependent organ that is subject to a wide variety of metabolic, hypoxic-ischemic, and infectious insults that result in cystic changes. Diagnosis of metabolic defects causing extensive cystic changes is particularly challenging for the pediatric pathologist, due to the rarity of these conditions. Pyruvate dehydrogenase (PDH) deficiency is one of the most common etiologies of congenital lactic acidosis, caused by mutations in subunits of the large mitochondrial matrix complex, and characterized by periventricular cysts, although few detailed reports focusing on neuropathologic findings exist. In addition, rare defects in other mitochondrial enzymes such as short-chain enoyl-CoA hydratase (SCEH, encoded by ECHS1 gene) can cause secondary PDH deficiency and present with neonatal lactic acidosis, but neuropathological findings have never been reported. Nonmetabolic conditions can also produce CNS cystic lesions, primarily in newborns. The pathologist must therefore distinguish between these etiologically disparate conditions which can produce CNS cavitary lesions. Here, we compare and contrast the gross and microscopic findings of cysts associated with cases of PDH and SCEH deficiencies with other neonatal cystic brain diseases including periventricular leukomalacia, neonatal Alexander disease, Canavan disease, and a case of cysts associated with a vascular abnormality. Our studies show that PDH and SCEH deficiencies are not grossly or histologically distinguishable from each other and both are associated with smooth-walled cysts largely limited to the telencephalic germinal matrix. Both show an absence of prominent hemosiderin deposits, Rosenthal fibers, vacuolization of the white matter, and gliosis or axonal damage in the surrounding parenchyma. These features can help distinguish PDH/SCEH deficiency from other pediatric/neonatal cystic CNS disorders, especially those produced by hypoxic ischemic conditions. Cysts, usually bilateral, confined to the telencephalic germinal matrix should elicit metabolic and genetic testing to appropriately diagnose PDH and SCEH and distinguish them from each other.

Inborn errors of metabolism leading to neuronal migration defects

The development and organisation of the human brain start in the embryonic stage and is a highly complex orchestrated process. It depends on series of cellular mechanisms that are precisely regulated by multiple proteins, signalling pathways and non-protein-coding genes. A crucial process during cerebral cortex development is the migration of nascent neuronal cells to their appropriate positions and their associated differentiation into layer-specific neurons. Neuronal migration defects (NMD) comprise a heterogeneous group of neurodevelopmental disorders including monogenetic disorders and residual syndromes due to damaging factors during prenatal development like infections, maternal diabetes mellitus or phenylketonuria, trauma, and drug use. Multifactorial causes are also possible. Classification into lissencephaly, polymicrogyria, schizencephaly, and neuronal heterotopia is based on the visible morphologic cortex anomalies. Characteristic clinical features of NMDs are severe psychomotor developmental delay, severe intellectual disability, intractable epilepsy, and dysmorphisms. Neurometabolic disorders only form a small subgroup within the large group of NMDs. The prototypes are peroxisomal biogenesis disorders, peroxisomal ß-oxidation defects and congenital disorders of O-glycosylation. The rapid evolution of biotechnology has resulted in an ongoing identification of metabolic and non-metabolic disease genes for NMDs. Nevertheless, we are far away from understanding the specific role of cortical genes and metabolites on spatial and temporal regulation of human cortex development and associated malformations. This limited understanding of the pathogenesis hinders the attempt for therapeutic approaches. In this article, we provide an overview of the most important cortical malformations and potential underlying neurometabolic disorders.

Neurometabolic disorders and congenital malformations of the central nervous system

Both malformations of the central nervous system and neurometabolic disorders are common, mainly in highly consanguineous populations. Both metabolic pathways and developmental pathways are closely related and interact with each other. Neurometabolic disorders can lead to disturbances in brain development through multiple mechanisms that include deficits in energy metabolism, critical nutrient deficiency, accumulation of neurotoxic substrates, abnormality in cell membrane constituents, and interference in cell-to-cell signaling pathways. The anomalies observed include absent or hypoplastic corpus callosum, midline brain defects, and malformations of the cortex, the cerebellum and the brain stem. Early diagnosis of an underlying inherited neurometabolic disorders is critical for the institution of treatment, which may positively influence prognosis, and allow for proper genetic counseling. In this review, we discuss those disorders in which the structural brain malformation is a dominant feature, and propose a practical approach that will permit a physician to investigate, and treat these disorders.

Synaptic energy metabolism and neuronal excitability, in sickness and health

Most of the energy produced in the brain is dedicated to supporting synaptic transmission. Glucose is the main fuel, providing energy and carbon skeletons to the cells that execute and support synaptic function: neurons and astrocytes, respectively. It is unclear, however, how glucose is provided to and used by these cells under different levels of synaptic activity. It is even more unclear how diseases that impair glucose uptake and oxidation in the brain alter metabolism in neurons and astrocytes, disrupt synaptic activity, and cause neurological dysfunction, of which seizures are one of the most common clinical manifestations. Poor mechanistic understanding of diseases involving synaptic energy metabolism has prevented the expansion of therapeutic options, which, in most cases, are limited to symptomatic treatments. To shed light on the intersections between metabolism, synaptic transmission, and neuronal excitability, we briefly review current knowledge of compartmentalized metabolism in neurons and astrocytes, the biochemical pathways that fuel synaptic transmission at resting and active states, and the mechanisms by which disorders of brain glucose metabolism disrupt neuronal excitability and synaptic function and cause neurological disease in the form of epilepsy.

Inborn errors of metabolism

Inborn errors of metabolism, also known as inherited metabolic diseases, constitute an important group of conditions presenting with neurologic signs in newborns. They are individually rare but collectively common. Many are treatable through restoration of homeostasis of a disrupted metabolic pathway. Given their frequency and potential for treatment, the clinician should be aware of this group of conditions and learn to identify the typical manifestations of the different inborn errors of metabolism. In this review, we summarize the clinical, laboratory, electrophysiologic, and neuroimaging findings of the different inborn errors of metabolism that can present with florid neurologic signs and symptoms in the neonatal period.

Prenatal sonographic description of fetuses affected by pyruvate dehydrogenase or pyruvate carboxylase deficiency

OBJECTIVE

Pyruvate dehydrogenase deficiency (PDHD) and pyruvate carboxylase deficiency (PCD) are diseases with severe neonatal forms, and their low prevalence makes them difficult to diagnose during pregnancy. Our objective was to describe prenatal ultrasound features that may be suggestive of these diagnoses.

METHODS

We analyzed 3 cases from our institution and reviewed 12 published cases of PDHD and 6 cases of PCD, recording all of the ultrasound signs, as well as magnetic resonance findings when available. Because of the small number of cases of PCD, we also included postnatal signs that could have been observed during imaging during pregnancy, for a total of 11 cases of PCD.

RESULTS

We conclude that PDHD can be suggested in the presence of ventriculomegaly or paraventricular cysts, associated with an abnormality of the cerebral parenchyma such as abnormal gyration or involvement of the corpus callosum. Pyruvate carboxylase deficiency can be suggested in the presence of ventriculomegaly, frontal horn impairment associated with subependymal, and paraventricular cysts.

CONCLUSION

When confronted to the ultrasound abnormalities we described, and after eliminating the most frequent etiologies, a metabolic deficiency should be considered. Furthermore, the hereditary character of these diseases makes that it is important to send the family with genetic advice in particular in case of history of a fetal death in utero or a death neonatal unexplained.

Massive parallel sequencing identifies RAPSN and PDHA1 mutations causing fetal akinesia deformation sequence

INTRODUCTION

Fetal akinesia deformation sequence (FADS) or arthrogryposis multiplex congenita (AMC) is characterized by clinical ambiguity and genetic heterogeneity, hampering genetic diagnosis via traditional sequencing methods. Next generation sequencing (NGS) of all known disease-causing genes offers an elegant solution to identify the genetic etiology of AMC/FADS in a diagnostic setting.

METHODS

An in-house developed disease-associated gene panel was conducted in two unrelated fetuses with FADS. First, a de novo analysis was performed on the entire disease-associated gene panel. If no pathogenic mutation was identified, analysis of variants retained in a specific subpanel with arthrogryposis/fetal akinesia-causing genes was performed.

RESULTS

In the first family, FADS relates to a homozygous c.484G > A (p.Glu162Lys) mutation in the gene RAPSN. The second case concerns a sporadic patient with brain anomalies and arthrogryposis due to a de novo hemizygous c.498C > T splice-site mutation in the pyruvate dehydrogenase-alpha 1 (PDHA1) gene.

DISCUSSION

NGS facilitated genetic diagnosis, and hence genetic counseling, for both families with AMC/FADS. Biallelic RAPSN mutations typically result in congenital myasthenia syndrome, or occasionally in FADS. This is the first report attributing the RAPSN mutation c.484G > A, identified in a homozygous state in patient 1, to FADS. The second patient represents the first case of AMC due to a PDHA1 mutation, advocating that pyruvate dehydrogenase deficiency should be considered in the differential diagnosis of fetal akinesia. This study illustrates the relevance of a disease-associated-gene panel as a diagnostic tool in pregnancies complicated by this genetically heterogeneous condition.