Metabolic and monogenic causes of seizures in neonates and young infants

Neonatal Seizures

Neonatal seizures are common among patients with acute brain injury or critical illness and can be difficult to diagnose and treat. The most common etiology of neonatal seizures is hypoxic-ischemic encephalopathy, with other common causes including ischemic stroke and intracranial hemorrhage. Neonatal clinicians can use a standardized approach to patients with suspected or confirmed neonatal seizures that entails laboratory testing, neuromonitoring, and brain imaging. The primary goals of management of neonatal seizures are to identify the underlying cause, correct it if possible, and prevent further brain injury. This article reviews recent evidence-based guidelines for the treatment of neonatal seizures and discusses the long-term outcomes of patients with neonatal seizures.

Neonatal seizures: stepping outside the comfort zone

Seizures are the most common neurological disorders in newborns. Managing neonatal seizures is challenging, especially for neurologists who are not neonatal specialists. Acute brain injury during ischemic insult is a key component of seizure occurrence, while genetic and metabolic disorders play less prevalent but more severe roles. The diagnosis of neonatal seizure is ambiguous, as the subjective differentiation between seizure and nonepileptic events is difficult; therefore, electrographic recording is the gold standard for diagnosis. The detection of electrographic seizures by neonatologists is currently facilitated by amplitude-integrated electroencephalography availability in many neonatal intensive care units. Although it is less sensitive than conventional electroencephalography, it is better to record all risky neonates to filter the abnormal events as early as possible to enable the initiation of dedicated therapy at proper dose and time and facilitate the initial response to antiepileptic drugs. This, in turn, helps maintain the balance between unnecessary drug use and their neurotoxic effects. Moreover, the early treatment of electrographic seizures plays a vital role in the suppression of subsequent abnormal brain electricity (status epilepticus) and shortening the hospital stay. An explicit understanding of seizure etiology and pathophysiology should direct attention to the proper prescription of short- and long-term antiepileptic medications to solve the challenging issue of whether neonatal seizures progress to postneonatal epilepsy and long-term cognitive deficits. This review addresses recent updates in different aspects of neonatal seizures, particularly electrographic discharge, including their definition, etiology, classification, diagnosis, management, and neurodevelopmental outcomes.

Seizures in the neonate: A review of etiologies and outcomes

Neonatal seizures occur in their majority in close temporal relation to an acute brain injury or systemic insult, and are accordingly defined as acute symptomatic or provoked seizures. However less frequently, unprovoked seizures may also present in the neonatal period as secondary to structural brain abnormalities, thus corresponding to structural epilepsies, or to genetic conditions, thus corresponding to genetic epilepsies. Unprovoked neonatal seizures should be thus considered as the clinical manifestation of early onset structural or genetic epilepsies that often have the characteristics of early onset epileptic encephalopathies. In this review, we address the conundrum of neonatal seizures including acute symptomatic, remote symptomatic, provoked, and unprovoked seizures, evolving to post-neonatal epilepsies, and neonatal onset epilepsies. The different clinical scenarios involving neonatal seizures, each with their distinct post-neonatal evolution are presented. The structural and functional impact of neonatal seizures on brain development and the concept of secondary epileptogenesis, with or without a following latent period after the acute seizures, are addressed. Finally, we underline the need for an early differential diagnosis between an acute symptomatic seizure and an unprovoked seizure, since it is associated with fundamental differences in clinical evolution. These are crucial aspects for neonatal management, counselling and prognostication. In view of the above aspects, we provide an outlook on future strategies and potential lines of research in this field.

Contemporary scope of inborn errors of metabolism involving epilepsy or seizures

Many inborn errors of metabolism may present with epilepsy or seizures, however, current scope of these diseases is unknown. Due to available precision medicine approaches in many inborn errors of metabolism and sophisticated traditional diagnostics, this group of disorders is of special relevance to clinicians. Besides, as current treatment is challenging and unsuccessful in more than 30% of all epilepsy patients, these diseases may provide valuable models for ictogenesis and epileptogenesis studies and potentially pave the ways to identification of novel treatments. The aim of this study was to elucidate genetic architecture of inborn errors of metabolism involving epilepsy or seizures and to evaluate their diagnostic approaches. After extensive search, 880 human genes were identified with a considerable part, 373 genes (42%), associated with inborn errors of metabolism. The most numerous group comprised disorders of energy metabolism (115, 31% of all inborn errors of metabolism). A substantial number of these diseases (26%, 97/373) have established specific treatments, therefore timely diagnosis comes as an obligation. Highly heterogenous, overlapping and non-specific phenotypes in most of inborn errors of metabolism presenting with epilepsy or seizures usually preclude phenotype-driven diagnostics. Besides, as traditional diagnostics involves a range of specialized metabolic tests with low diagnostic yields and is generally inefficient and lengthy, next-generation sequencing-based methods were proposed as a cost-efficient one-step way to shorten "diagnostic odyssey". Extensive list of 373 epilepsy- or seizures-associated inborn errors of metabolism genes may be of value in development of gene panels and as a tool for variants' filtration.

Metabolic etiologies in West syndrome

West syndrome (WS) is an early life epileptic encephalopathy associated with infantile spasms, interictal electroencephalography (EEG) abnormalities including high amplitude, disorganized background with multifocal epileptic spikes (hypsarrhythmia), and often neurodevelopmental impairments. Approximately 64% of the patients have structural, metabolic, genetic, or infectious etiologies and, in the rest, the etiology is unknown. Here we review the contribution of etiologies due to various metabolic disorders in the pathology of WS. These may include metabolic errors in organic molecules involved in amino acid and glucose metabolism, fatty acid oxidation, metal metabolism, pyridoxine deficiency or dependency, or acidurias in organelles such as mitochondria and lysosomes. We discuss the biochemical, clinical, and EEG features of these disorders as well as the evidence of how they may be implicated in the pathogenesis and treatment of WS. The early recognition of these etiologies in some cases may permit early interventions that may improve the course of the disease.

A population-based cost-effectiveness study of early genetic testing in severe epilepsies of infancy

OBJECTIVE

The severe epilepsies of infancy (SEI) are a devastating group of disorders that pose a major care and economic burden on society; early diagnosis is critical for optimal management. This study sought to determine the incidence and etiologies of SEI, and model the yield and cost-effectiveness of early genetic testing.

METHODS

A population-based study was undertaken of the incidence, etiologies, and cost-effectiveness of a whole exome sequencing-based gene panel (targeted WES) in infants with SEI born during 2011-2013, identified through electroencephalography (EEG) and neonatal databases. SEI was defined as seizure onset before age 18 months, frequent seizures, epileptiform EEG, and failure of ≥2 antiepileptic drugs. Medical records, investigations, MRIs, and EEGs were analyzed, and genetic testing was performed if no etiology was identified. Economic modeling was performed to determine yield and cost-effectiveness of investigation of infants with unknown etiology at epilepsy onset, incorporating targeted WES at different stages of the diagnostic pathway.

RESULTS

Of 114 infants with SEI (incidence = 54/100 000 live births/y), the etiology was determined in 76 (67%): acquired brain injuries (n = 14), focal cortical dysplasias (n = 14), other brain malformations (n = 17), channelopathies (n = 11), chromosomal (n = 9), metabolic (n = 6), and other genetic (n = 5) disorders. Modeling showed that incorporating targeted WES increased diagnostic yield compared to investigation without targeted WES (48/86 vs 39/86). Early targeted WES had lower total cost ($677 081 U.S. dollars [USD] vs $738 136 USD) than late targeted WES. A pathway with early targeted WES and limited metabolic testing yielded 7 additional diagnoses compared to investigation without targeted WES (46/86 vs 39/86), with lower total cost ($455 597 USD vs $661 103 USD), lower cost per diagnosis ($9904 USD vs $16 951 USD), and a dominant cost-effectiveness ratio.

SIGNIFICANCE

Severe epilepsies occur in 1 in 2000 infants, with the etiology identified in two-thirds, most commonly malformative. Early use of targeted WES yields more diagnoses at lower cost. Early genetic diagnosis will enable timely administration of precision medicines, once developed, with the potential to improve long-term outcome.

Profile of neonatal epilepsies: Characteristics of a prospective US cohort

OBJECTIVE

Although individual neonatal epilepsy syndromes are rare, as a group they represent a sizable subgroup of neonatal seizure etiologies. We evaluated the profile of neonatal epilepsies in a prospective cohort of newborns with seizures.

METHODS

Consecutive newborns with seizures were enrolled in the Neonatal Seizure Registry (an association of 7 US children's hospitals). Treatment and diagnostic testing were at the clinicians' discretion. Neonates with seizures related to epileptic encephalopathies (without structural brain abnormalities), brain malformations, or benign familial epilepsies were included in this analysis.

RESULTS

Among 611 consecutive newborns with seizures, 79 (13%) had epilepsy (35 epileptic encephalopathy, 32 congenital brain malformations, 11 benign familial neonatal epilepsy [BFNE], 1 benign neonatal seizures). Twenty-nine (83%) with epileptic encephalopathy had genetic testing and 24/29 (83%) had a genetic etiology. Pathogenic or likely pathogenic KCNQ2 variants (n = 10) were the most commonly identified etiology of epileptic encephalopathy. Among 23 neonates with brain malformations who had genetic testing, 7 had putative genetic etiologies. Six infants with BFNE had genetic testing; 3 had pathogenic KCNQ2 variants and 1 had a pathogenic KCNQ3 variant. Comorbid illnesses that predisposed to acute symptomatic seizures occurred in 3/35 neonates with epileptic encephalopathy vs 10/32 with brain malformations (p = 0.03). Death or discharge to hospice were more common among newborns with brain malformations (11/32) than those with epileptic encephalopathy (3/35, p = 0.01).

CONCLUSIONS

Neonatal epilepsy is often due to identifiable genetic causes. Genetic testing is now warranted for newborns with epilepsy in order to guide management and inform discussions of prognosis.

Inborn Errors of Metabolism and Epilepsy: Current Understanding, Diagnosis, and Treatment Approaches

Inborn errors of metabolism (IEM) are a rare cause of epilepsy, but seizures and epilepsy are frequently encountered in patients with IEM. Since these disorders are related to inherited enzyme deficiencies with resulting effects on metabolic/biochemical pathways, the term “metabolic epilepsy” can be used to include these conditions. These epilepsies can present across the life span, and share features of refractoriness to anti-epileptic drugs, and are often associated with co-morbid developmental delay/regression, intellectual, and behavioral impairments. Some of these disorders are amenable to specific treatment interventions; hence timely and appropriate diagnosis is critical to improve outcomes. In this review, we discuss those disorders in which epilepsy is a dominant feature and present an approach to the clinical recognition, diagnosis, and management of these disorders, with a greater focus on primarily treatable conditions. Finally, we propose a tiered approach that will permit a clinician to systematically investigate, identify, and treat these rare disorders.

Nonketotic hyperglycinemia: Functional assessment of missense variants in GLDC to understand phenotypes of the disease

The rapid analysis of genomic data is providing effective mutational confirmation in patients with clinical and biochemical hallmarks of a specific disease. This is the case for nonketotic hyperglycinemia (NKH), a Mendelian disorder causing seizures in neonates and early-infants, primarily due to mutations in the GLDC gene. However, understanding the impact of missense variants identified in this gene is a major challenge for the application of genomics into clinical practice. Herein, a comprehensive functional and structural analysis of 19 GLDC missense variants identified in a cohort of 26 NKH patients was performed. Mutant cDNA constructs were expressed in COS7 cells followed by enzymatic assays and Western blot analysis of the GCS P-protein to assess the residual activity and mutant protein stability. Structural analysis, based on molecular modeling of the 3D structure of GCS P-protein, was also performed. We identify hypomorphic variants that produce attenuated phenotypes with improved prognosis of the disease. Structural analysis allows us to interpret the effects of mutations on protein stability and catalytic activity, providing molecular evidence for clinical outcome and disease severity. Moreover, we identify an important number of mutants whose loss-of-functionality is associated with instability and, thus, are potential targets for rescue using folding therapeutic approaches.

Epileptic Encephalopathy in Childhood: A Stepwise Approach for Identification of Underlying Genetic Causes

Epilepsy is one of the most common neurological disorders in childhood. Epilepsy associated with global developmental delay and cognitive dysfunction is defined as epileptic encephalopathy. Certain inherited metabolic disorders presenting with epileptic encephalopathy can be treated with disease specific diet, vitamin, amino acid or cofactor supplementations. In those disorders, disease specific therapy is successful to achieve good seizure control and improve long-term neurodevelopmental outcome. For this reason, intractable epilepsy with global developmental delay or history of developmental regression warrants detailed metabolic investigations for the possibility of an underlying treatable inherited metabolic disorder, which should be undertaken as first line investigations. An underlying genetic etiology in epileptic encephalopathy has been supported by recent studies such as array comparative genomic hybridization, targeted next generation sequencing panels, whole exome and whole genome sequencing. These studies report a diagnostic yield up to 70%, depending on the applied genetic testing as well as number of patients enrolled. In patients with epileptic encephalopathy, a stepwise approach for diagnostic work-up will help to diagnose treatable inherited metabolic disorders quickly. Application of detailed genetic investigations such as targeted next generation sequencing as second line and whole exome sequencing as third line testing will diagnose underlying genetic disease which will help for genetic counseling as well as guide for prenatal diagnosis. Knowledge of underlying genetic cause will provide novel insights into the pathogenesis of epileptic encephalopathy and pave the ground towards the development of targeted neuroprotective treatment strategies to improve the health outcome of children with epileptic encephalopathy.

Normal Neurodevelopmental Outcomes in PNPO Deficiency: A Case Series and Literature Review

Pyridox(am)ine 5'-phosphate oxidase deficiency results in an early-onset neonatal encephalopathy that can be fatal if not detected and treated early. The condition is rare, can result in preterm delivery, and can mimic hypoxic ischemic encephalopathy. Thus, suspicion of the diagnosis, appropriate investigations, and therapeutic trials with pyridoxal-5'-phosphate are often delayed. In this paper we report four cases of pyridox(am)ine 5'-phosphate oxidase deficiency, two of whom are siblings. Three were treated with pyridoxal-5'-phosphate in the first few days of life and the fourth within the first month. One of the siblings was electively treated from birth until a diagnosis was secured. Our cases demonstrate that early diagnosis and treatment can be associated with normal neurodevelopment in childhood. We suggest that a low threshold for investigating for pyridox(am)ine 5'-phosphate oxidase deficiency and electively treating with pyridoxal-5'-phosphate is considered in any neonate with encephalopathy, including those with presumed hypoxic ischemic encephalopathy in whom the degree of encephalopathy is not expected from perinatal history, cord gases and/or neuroimaging.

Familial neonatal seizures in 36 families: Clinical and genetic features correlate with outcome

OBJECTIVE

We evaluated seizure outcome in a large cohort of familial neonatal seizures (FNS), and examined phenotypic overlap with different molecular lesions.

METHODS

Detailed clinical data were collected from 36 families comprising two or more individuals with neonatal seizures. The seizure course and occurrence of seizures later in life were analyzed. Families were screened for KCNQ2, KCNQ3, SCN2A, and PRRT2 mutations, and linkage studies were performed in mutation-negative families to exclude known loci.

RESULTS

Thirty-three families fulfilled clinical criteria for benign familial neonatal epilepsy (BFNE); 27 of these families had KCNQ2 mutations, one had a KCNQ3 mutation, and two had SCN2A mutations. Seizures persisting after age 6 months were reported in 31% of individuals with KCNQ2 mutations; later seizures were associated with frequent neonatal seizures. Linkage mapping in two mutation-negative BFNE families excluded linkage to KCNQ2, KCNQ3, and SCN2A, but linkage to KCNQ2 could not be excluded in the third mutation-negative BFNE family. The three remaining families did not fulfill criteria of BFNE due to developmental delay or intellectual disability; a molecular lesion was identified in two; the other family remains unsolved.

SIGNIFICANCE

Most families in our cohort of familial neonatal seizures fulfill criteria for BFNE; the molecular cause was identified in 91%. Most had KCNQ2 mutations, but two families had SCN2A mutations, which are normally associated with a mixed picture of neonatal and infantile onset seizures. Seizures later in life are more common in BFNE than previously reported and are associated with a greater number of seizures in the neonatal period. Linkage studies in two families excluded known loci, suggesting a further gene is involved in BFNE.

Neonatal Seizures: Impact on Neurodevelopmental Outcomes

Neonatal period is the most vulnerable time for the occurrence of seizures, and neonatal seizures often pose a clinical challenge both for their acute management and frequency of associated long-term co-morbidities. Etiologies of neonatal seizures are known to play a primary role in the anti-epileptic drug responsiveness and the long-term sequelae. Recent studies have suggested that burden of acute recurrent seizures in neonates may also impact chronic outcomes independent of the etiology. However, not many studies, either clinical or pre-clinical, have addressed the long-term outcomes of neonatal seizures in an etiology-specific manner. In this review, we briefly review the available clinical and pre-clinical research for long-term outcomes following neonatal seizures. As the most frequent cause of acquired neonatal seizures, we focus on the studies evaluating long-term effects of HIE-seizures with the goal to evaluate (1) what parameters evaluated during acute stages of neonatal seizures can reliably be used to predict long-term outcomes? and (2) what available clinical and pre-clinical data are available help determine importance of etiology vs. seizure burdens in long-term sequelae.

Epidemiology and aetiology of neonatal seizures

Neonatal seizures constitute the most frequent and distinctive neurological symptom in the neonatal period. Seizures in the neonatal period differ considerably from those observed later in life with respect to their aetiological profile and clinical presentation. In addition, the aetiological profile in preterm infants is different from that seen in term infants. Hypoxic-ischaemic encephalopathy is the most frequent cause of neonatal seizures in term babies followed by focal ischaemia (stroke), cerebral malformations and metabolic disturbances. In preterm neonates, intraventricular haemorrhage and infections cause most of the seizures reported in this group. Better neuroimaging techniques have reduced the number of undiagnosed cases, and the institution of newer neuroprotective strategies has influenced the outcome.

Neonatal neuroimaging findings in inborn errors of metabolism

Individually, metabolic disorders are rare, but overall they account for a significant number of neonatal disorders affecting the central nervous system. The neonatal clinical manifestations of inborn errors of metabolism (IEMs) are characterized by nonspecific systemic symptoms that may mimic more common acute neonatal disorders like sepsis, severe heart insufficiency, or neonatal hypoxic-ischemic encephalopathy. Certain IEMs presenting in the neonatal period may also be complicated by sepsis and cardiomyopathy. Early diagnosis is mandatory to prevent death and permanent long-term neurological impairments. Although neuroimaging findings are rarely specific, they play a key role in suggesting the correct diagnosis, limiting the differential diagnosis, and may consequently allow early initiation of targeted metabolic and genetic laboratory investigations and treatment. Neuroimaging may be especially helpful to distinguish metabolic disorders from other more common causes of neonatal encephalopathy, as a newborn may present with an IEM prior to the availability of the newborn screening results. It is therefore important that neonatologists, pediatric neurologists, and pediatric neuroradiologists are familiar with the neuroimaging findings of metabolic disorders presenting in the neonatal time period.