A novel PIGA mutation in a Taiwanese family with early-onset epileptic encephalopathy

Early-Onset Dystonia and Visual Impairment Preceding Epileptic Encephalopathy Associated with PIGA Gene Mutation

The association between dystonia and early-onset epileptic encephalopathy (EOEE) may have a genetic basis. Phosphatidylinositol glycan biosynthesis class A protein (PIGA) germline mutations have been described in the last decade and associated with refractory EOEEs. Dysmorphisms and visceral abnormalities have also been reported. Here, we present the case of a now 8-month-old child who was evaluated for dystonia, visual impairment, and developmental delay at 2 months of age, followed by refractory focal seizures when he was 4 months old. The remaining examination was normal, besides an accelerated linear growth. His brain magnetic resonance and an extensive metabolic investigation failed to show any abnormalities. At 7 months of age, the exome sequencing found a hemizygous PIGA pathogenic variant-c.1352T > C (p.(Ile451Thr). Seizures improved after the association of carbamazepine with levetiracetam and the beginning of the ketogenic diet. To our knowledge, this is the first time the phenotype associated with this specific mutation is described. Our patient had the singularity of manifesting with remarkable dystonia, over 2 months before the onset of seizures. We also point to the utility of the gene sequencing approach in the diagnosis of patients with dystonia and EOEEs, since identification of the genetic cause may help in patient's management and families' empowerment.

Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome 2 Caused by a Novel PIGA Variant Not Associated with a Skewed X-Inactivation Pattern

Germline variants in the phosphatidylinositol glycan class A (PIGA) gene, which is involved in glycosylphosphatidylinositol (GPI) biosynthesis, cause multiple congenital anomalies-hypotonia-seizures syndrome 2 (MCAHS2) with X-linked recessive inheritance. The available literature has described a pattern of almost 100% X-chromosome inactivation in mothers carrying PIGA variants. Here, we report a male infant with MCAHS2 caused by a novel PIGA variant inherited from his mother, who has a non-skewed pattern of X inactivation. Phenotypic evidence supporting the pathogenicity of the variant was obtained by flow-cytometry tests. We propose that the assessment in neutrophils of the expression of GPI-anchored proteins (GPI-APs), especially CD16, should be considered in cases with variants of unknown significance with random X-inactivation in carrier mothers in order to clarify the pathogenic role of PIGA or other gene variants linked to the synthesis of GPI-APs.

High-dose pyridoxine treatment for inherited glycosylphosphatidylinositol deficiency

OBJECTIVE

We aimed to assess the efficacy and safety of high-dose pyridoxine treatment for seizures and its effects on development in patients with inherited glycosylphosphatidylinositol deficiencies (IGDs).

METHODS

In this prospective open-label multicenter pilot study, we enrolled patients diagnosed with IGDs using flow cytometry and/or genetic tests. The patients received oral pyridoxine (20-30 mg/kg/day) for 1 year, in addition to previous treatment.

RESULTS

All nine enrolled patients (mean age: 66.3 ± 44.3 months) exhibited marked decreases in levels of CD16, a glycosylphosphatidylinositol-anchored protein, on blood granulocytes. The underlying genetic causes of IGDs were PIGO, PIGL, and unknown gene mutations in two, two, and five patients, respectively. Six patients experienced seizures, while all patients presented with developmental delay (mean developmental age: 11.1 ± 8.1 months). Seizure frequencies were markedly (>50%) and drastically (>90%) reduced in three and one patients who experienced seizures, respectively. None of the patients presented with seizure exacerbation. Eight of nine patients exhibited modest improvements in development (P = 0.14). No adverse events were observed except for mild transient diarrhea in one patient.

CONCLUSION

One year of daily high-dose pyridoxine treatment was effective in the treatment of seizures in more than half of our patients with IGDs and modestly improved development in the majority of them. Moreover, such treatment was reasonably safe. These findings indicate that high-dose pyridoxine treatment may be effective against seizures in patients with IGDs, although further studies are required to confirm our findings. (University Hospital Medical Information Network Clinical Trials Registry [UMIN-CTR] number: UMIN000024185.).

Limb-clasping, cognitive deficit and increased vulnerability to kainic acid-induced seizures in neuronal glycosylphosphatidylinositol deficiency mouse models

Posttranslational modification of a protein with glycosylphosphatidylinositol (GPI) is a conserved mechanism exists in all eukaryotes. Thus far, >150 human GPI-anchored proteins have been discovered and ~30 enzymes have been reported to be involved in the biosynthesis and maturation of mammalian GPI. Phosphatidylinositol glycan biosynthesis class A protein (PIGA) catalyzes the very first step of GPI anchor biosynthesis. Patients carrying a mutation of the PIGA gene usually suffer from inherited glycosylphosphatidylinositol deficiency (IGD) with intractable epilepsy and intellectual developmental disorder. We generated three mouse models with PIGA deficits specifically in telencephalon excitatory neurons (Ex-M-cko), inhibitory neurons (In-M-cko) or thalamic neurons (Th-H-cko), respectively. Both Ex-M-cko and In-M-cko mice showed impaired long-term fear memory and were more susceptible to kainic acid-induced seizures. In addition, In-M-cko demonstrated a severe limb-clasping phenotype. Hippocampal synapse changes were observed in Ex-M-cko mice. Our Piga conditional knockout mouse models provide powerful tools to understand the cell-type specific mechanisms underlying inherited GPI deficiency and to test different therapeutic modalities.

Deciphering the premature mortality in PIGA-CDG - An untold story

OBJECTIVE

Congenital disorder of glycosylation (CDG) due to a defective phosphatidylinositol glycan anchor biosynthesis class A protein (PIGA) is a severe X-linked developmental and epileptic encephalopathy. Seizures are often treatment refractory, and patients have intellectual disability and global developmental delay. Previous reports have suggested that patients with PIGA-CDG have a high risk of premature mortality. This study aimed to evaluate the observed high mortality and the causes of death in PIGA-CDG patients.

METHODS

We reviewed the literature and collected additional unpublished patients through an international network.

RESULTS

In total, we reviewed the data of 88 patients of whom 30 patients born alive were deceased, and the overall mortality before the age of 20 years was 30 % (26/88). Age at death ranged from 15 days to 48 years of life. The median age at death was two years and more than half of the patients deceased in early childhood. The PIGA-specific mortality rate/1000 person-years was 44.9/1000 person-years (95 %, CI 31.4-64.3). There were no cases of definite or probable sudden unexpected death in epilepsy (SUDEP) and half of the patients died due to respiratory failure (15/30, 50 %) or possible SUDEP (3/30, 10 %). Three patients (10 %) died from severe cardiomyopathy, liver failure and gastrointestinal bleeding, respectively. The cause of death was unclassified in nine patients (30 %). Autopsies were rarely performed and the true cause of death remains unknown for the majority of patients.

SIGNIFICANCE

Our data indicate an increased risk of premature death in patients with PIGA-CDG when compared to most monogenic developmental and epileptic encephalopathies.

Early-onset epileptic encephalopathy related to germline PIGA mutations: A series of 5 cases

The molecular diagnosis of early-onset epileptic encephalopathy (EOEE), an expanding field in child neurology, is becoming increasingly possible thanks to the widespread availability of next-generation sequencing and whole-exome sequencing. In the past 15 years, mutations in STXBP1, KCNQ2, SCN2A, SCN8A and numerous other genes have been reported, giving a more accurate insight for these rare diseases. Among these genes, germline mutations in Phosphatidyl Inositol Glycan A (PIGA) gene were first reported in 2012. Located on Xp22.2, PIGA is involved in the synthesis of GPI (glycosylphosphatidylinositol) which acts as a membrane anchor for different proteins: enzymes, adhesion molecules, regulation of the complement way, and co-receptor in transduction signal. Children suffering from this condition exhibit developmental delay with early-onset epilepsy, severe dysmorphic signs, multi-visceral anomalies and early death in the most severe forms. Here, we report five cases of germline PIGA mutations, with two missense mutations that have not been reported to date. We provide a new insight into the electroclinical phenotype. At the onset, epileptic spasms and focal-onset seizures with upper limbs and ocular involvements were present. Epilepsy proved pharmacoresistant in 4 out of 5 cases. Interictal EEG may be normal at the onset of epilepsy, but abnormalities in electroencephalographic studies were eventually present in all cases. Different types of seizures may be present simultaneously, and epileptic phenotypes evolve with aging.

Analyzing clinical and genetic characteristics of a cohort with multiple congenital anomalies-hypotonia-seizures syndrome (MCAHS)

Objective

To summarize and extend the phenotypic characterization of Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome, and to discuss genotype-phenotype correlations.

Methods

Collecting clinical information of 17 patients with pathogenic variants in PIGN, PIGA, and PIGT. Genetic studies were performed on all patients.

Results

There were 7 patients with 15 PIGN mutations (one patient carrying 3 mutations), 8 patients with 8 PIGA mutations, and 2 patients with 5 PIGT mutations (one patient carrying 3 mutations). All patients had epilepsy and developmental delay, with 71% of them showed hypotonia. And among these patients’ various seizure types, the focal seizure was the most common one. Eighty-two percent patients showed a significant relationship between seizures and fever. Serum ALP was elevated in one patient with PIGN mutations and in two patients with PIGA mutations. Brain MRI showed enlarged subarachnoid space in 56% of patients. Some other different characteristics had also been found in our patients: First, atypical absence seizures presented in three patients with PIGN mutations; Second, diffuse slow waves mixed with focal or multifocal discharges of interictal EEG in 88% cases with PIGA-deficient; Third, phenotypes of seven out of eight patients with PIGA mutations were difficult to be classified as severe or less severe group; Last, mild neurological symptoms and developmental status rather than severe conditions occurred in one patient with PIGT mutations.

Conclusion

With epilepsy, developmental delay, and/or hypotonia as common features, the knowledge of MCAHS in terms of phenotype and genotype has been expanded. In cases with PIGN-deficient, we expanded the types of atypical absence seizures, and described one patient with elevated serum ALP. Focal seizures with diffuse slow waves mixed with focal or multifocal discharges on EEG rather than infantile spasms with hypsarrhythmia, which as previously reported were often seen in our patients with PIGA mutations. The classifications of phenotypes caused by PIGA mutations should be more continuous than discrete. The mild phenotype of one patient with PIGT mutations expanded the clinical presentation of MCAHS3.

A Novel Mutation in PIGA Associated with Multiple Congenital Anomalies-Hypotonia-Seizure Syndrome 2 (MCAHS2) in a Boy with a Combination of Severe Epilepsy and Gingival Hyperplasia

Multiple congenital anomalies-hypotonia-seizures syndrome 2 (MCAHS2) is a rare disease caused by mutations in the X chromosomal PIGA gene. Clinically it is characterized by early-onset epilepsy, hypotonia, dysmorphic features, and variable congenital anomalies. PIGA codes for the phosphatidylinositol glycan-class A protein, which forms a subunit of an enzymatic complex involved in glycophosphatidylinositol (GPI) biosynthesis. We present a new case of MCAHS2 and perform a comprehensive review of the available literature to delineate the phenotypical traits associated with germline PIGA mutations. Furthermore, we provide functional evidence of pathogenicity of the novel missense mutation, c.154C>T; (p.His52Tyr), in the PIGA gene causative of MCAHS2 in our patient. By flow cytometry, we observed reduced expression of GPI-anchored surface proteins in patient granulocytes compared to control samples, proving GPI-biogenesis impairment. The patient's severe epilepsy with several daily attacks was refractory to treatment, but the frequency of seizures reduced temporarily under triple therapy with perampanel, rufinamide and vigabatrin. Our study delineates the known MCAHS2 phenotype and discusses challenges of diagnosis and clinical management in this complex, rare disease. Furthermore, we present a novel mutation with functional evidence of pathogenicity.

PIGA related disorder as a range of phenotypes rather than two distinct subtypes

Patients with germline phosphatidylinositol glycan biosynthesis class A (PIGA) related disorder have historically been categorized into one of two distinct subtypes: a severe form which is often fatal, and a less severe form. However, the increasing number of cases with features indicative of both subtypes raise the possibility of a phenotypic spectrum associated with PIGA disorder. In order to further characterize this phenotypic spectrum, we present two patients with features of both the severe and less severe subtypes with a review of phenotypes reported to date in the literature. In eight year old patient 1, a maternally inherited PIGA likely pathogenic variant was discovered using exome sequencing. He presented with myoclonic epilepsy, mild intellectual disability, spastic diplegia, developmental motor delay, and autism spectrum disorder. Patient 2 is a 13 year old with focal epilepsy, profound developmental delay, coarse facial features, severe intellectual disability and autism spectrum disorder. A de novo PIGA likely pathogenic variant was found through exome sequencing. Both patients had normal alkaline phosphatase levels and are without related organ abnormalities. We conclude that pathogenic PIGA variants cause a spectrum of phenotypes rather than the categories of "severe" and "less severe" as previously posited.