Mabry Syndrome Research Articles

Rare Genetic Developmental Disabilities: Mabry Syndrome (MIM 239300) Index Cases and Glycophosphatidylinositol (GPI) Disorders.

The case report by Mabry et al. (1970) of a family with four children with elevated tissue non-specific alkaline phosphatase, seizures and profound developmental disability, became the basis for phenotyping children with the features that became known as Mabry syndrome. Aside from improvements in the services available to patients and families, however, the diagnosis and treatment of this, and many other developmental disabilities, did not change significantly until the advent of massively parallel sequencing. As more patients with features of the Mabry syndrome were identified, exome and genome sequencing were used to identify the glycophosphatidylinositol (GPI) biosynthesis disorders (GPIBDs) as a group of congenital disorders of glycosylation (CDG). Biallelic variants of the phosphatidylinositol glycan (PIG) biosynthesis, type V (PIGV) gene identified in Mabry syndrome became evidence of the first in a phenotypic series that is numbered HPMRS1-6 in the order of discovery. HPMRS1 [MIM: 239300] is the phenotype resulting from inheritance of biallelic PIGV variants. Similarly, HPMRS2 (MIM 614749), HPMRS5 (MIM 616025) and HPMRS6 (MIM 616809) result from disruption of the PIGO, PIGW and PIGY genes expressed in the endoplasmic reticulum. By contrast, HPMRS3 (MIM 614207) and HPMRS4 (MIM 615716) result from disruption of post attachment to proteins PGAP2 (HPMRS3) and PGAP3 (HPMRS4). The GPI biosynthesis disorders (GPIBDs) are currently numbered GPIBD1-21. Working with Dr. Mabry, in 2020, we were able to use improved laboratory diagnostics to complete the molecular diagnosis of patients he had originally described in 1970. We identified biallelic variants of the PGAP2 gene in the first reported HPMRS patients. We discuss the longevity of the Mabry syndrome index patients in the context of the utility of pyridoxine treatment of seizures and evidence for putative glycolipid storage in patients with HPMRS3. From the perspective of the laboratory innovations made that enabled the identification of the HPMRS phenotype in Dr. Mabry's patients, the need for treatment innovations that will benefit patients and families affected by developmental disabilities is clear.

Individual Treatment Trial of PIGV-Associated Mabry Syndrome with D-Mannose in a Young Child

We describe the first individual treatment trial with D-mannose in a young girl with PIGV-CDG. PIGV-CDG belongs to the GPI anchor deficiencies leading to intellectual disability, dysmorphic features, epilepsy, and, less frequently, organ malformations. A hallmark of the GPI anchor deficiencies is the elevated serum alkaline phosphatase (AP). Our patient carried the germline homozygous PIGV variant c.1022C>A, p. (Ala341Glu), the most commonly reported pathogenic variant leading to PIGV-CDG so far. We aimed to improve the impaired enzymatic function of PIGV through elevated substrate levels by giving D-mannose orally. We monitored the clinical status, developmental progress as well as serum AP levels. Our patient experienced no side effects. Standardized developmental testing showed better developmental progress during the 21-month treatment period with D-mannose than in the 12 months following the discontinuation of treatment. The D-Mannose treatment might have had a positive effect on the development of our patient with PIGV-CDG.

Two South African patients with PGAP3-related Mabry syndrome with unusually low alkaline phosphatase levels


 
 
 
 Hyperphosphatasia with mental retardation syndrome (HPMRS), also known as Mabry syndrome, is an autosomal recessive disease that is associated with inherited glycosylphosphatidylinositol (GPI) deficiencies. This genetically heterogeneous disorder can be caused by variants in seven genes that encode molecules of the glycosylphosphatidylinositol (GPI)-anchor biosynthesis pathway, namely PIGL, PIGO, PIGV, PIGW, PIGY, PGAP2 and PGAP3. Recently, a pathogenic variant in PGAP3 was identified in 3 unrelated South African patients with HMPRS. Here, two further patients with the exact variant in PGAP3 are described. Classically, HMPRS is associated with elevated alkaline phosphatase (ALP) levels. Interestingly, these two patients had unusually low ALP levels at initial presentation. This is an important observation, as the ALP level is often used as a screening test to decide whether to proceed to confirmatory genetic testing. These patients illustrate that in PGAP3-related Mabry syndrome, ALP levels can be low, albeit a rare finding. Hence, a high suspicion for the disorder should be maintained in patients with typical facial dysmorphic features and severe neurodevelopmental delay, even in the absence of elevated ALP.
 
 
 

Congenital diaphragmatic hernia and early lethality in PIGL-related disorder

We report on three male siblings who presented prenatally with a nearly identical combination of congenital anomalies and who died shortly after preterm birth. The first baby was a singleton pregnancy, and the other two babies were dichorionic diamniotic twins. Key features included: left-sided congenital diaphragmatic hernia, inferior vermian dysgenesis/hypoplasia, prenasal edema, cleft palate, micropenis/ambiguous genitalia (in 2 of 3 babies), bilateral renal pelvic dilatation (in twins, first baby showed slightly enlarged kidneys) and polyhydramnios (in 2 of 3). Whole genome sequencing performed on DNA from all three babies revealed homozygous missense PIGL gene variants: c.438C>A, p.(Phe146Leu). Both parents were heterozygous carriers of the variant. The reporting clinical laboratory classified the change as a variant of uncertain significance (VUS), and concluded “A genetic diagnosis of autosomal recessive CHIME syndrome is possible”. The PIGL gene has been reported to cause two different autosomal recessive conditions: CHIME syndrome and Mabry syndrome. CHIME (Zunich neuroectodermal syndrome) is characterized by ocular Colobomas, Heart defects, Ichthyosiform dermatosis, Mental retardation (intellectual disability), and Ear anomalies, including conductive hearing loss. Mabry [aka hyperphosphatasia mental retardation syndrome (HPMRS)] is characterized by severe developmental delay, moderate to severe intellectual disability, distinctive facial features, brachytelephalangy, increased serum levels of alkaline phosphatase (ALP), and recurrent seizures. Neonatal demise and lack of postmortem examination precluded assessment of some key features (including seizures, developmental delay, ALP levels, colobomas and deafness), but overlapping features observed included cleft palate, brain anomalies, genitourinary abnormalities and prenasal edema. Notably, diaphragmatic hernia is not a common feature of either condition, but is a cardinal feature of Fryns syndrome. The genetic etiology of Fryns syndrome has not been definitively established, although, much like CHIME and Mabry syndrome, can be caused by variants in glycosylphosphatidylinositol (GPI) anchor pathway genes. Our findings suggest further overlap between inherited GPI deficiencies, and possible expansion of the clinical phenotype of PIGL-related disorders to include prenatal presentations with congenital diaphragmatic hernia. Although reported as a VUS, we present phenotypic and familial segregation evidence that supports likely pathogenicity of the c.438C>A variant.

ПЕРВОЕ В РОССИИ КЛИНИЧЕСКОЕ НАБЛЮДЕНИЕ РЕБЕНКА С СИНДРОМОМ МАБРИ (ГИПЕРФОСФАТАЗИЕЙ, УМСТВЕННОЙ ОТСТАЛОСТЬЮ И ЭПИЛЕПСИЕЙ) В СОЧЕТАНИИ С БОЛЕЗНЬЮ ГИРШПРУНГА

The article presents a literature review of a rare congenital disease, hyperphosphatasia syndrome with mental retardation (Mabry's syndrome) in children. This syndrome is characterized by a triad of symptoms: hyperphosphatasia, epilepsy and mental retardation, often associated developmental defects. To date, 114 patients have been described. The review presents the available literary sources with clinical observations of patients since 1970, when the syndrome was first described by the pediatrician Ch. Mabry. The data on genetic defects leading to the disease are presented. The scheme of development of pyridoxine-sensitive epilepsy, the most severe manifestation of the syndrome, is described. The first clinical case of the patient with Mabry's syndrome in combination with Hirschsprung's disease in Russia is described.

PIGO variants in a boy with features of Mabry syndrome who also exhibits Fryns syndrome with peripheral neuropathy

AbstractWe report a 2‐year‐old boy with left congenital diaphragmatic defect (CDH), pulmonary hypoplasia, and polyhydramnios who harbors compound heterozygous mutations, c.1109A>G and c.2497_2498del, in the PIGO gene. The facial appearance was characterized by cloudy cornea, broad and flat nasal bridge, long philtrum, low‐set ears, and micrognathia. Serum alkaline phosphatase level was consistently elevated, suggesting that he meets the criteria for Mabry syndrome. However, the observation of other anomalies including micropenis, cryptorchidism, and Hirschsprung disease suggests clinical features compatible with Fryns syndrome (FS). Left CDH and Hirschsprung disease were surgically repaired at 1 week and 3 months of age, respectively. He also exhibited multiple joint contractures and markedly decreased voluntary movement. Craw hands were seen but pes cavus was absent. Electrophysiology studies showed diffuse axonal demyelinating neuropathy. The cell surface expression of CD16, CD24, and CD59 on blood granulocytes was significantly reduced. The PIGO gene encodes ethanolamine phosphate transferase 3 in the glycosylphosphatidylinositol (GPI) biosynthesis pathway. Mutations in the gene are known to cause Mabry syndrome, an inherited GPI deficiency (IGD) characterized by hyperphosphatasia. IGDs show clinical heterogeneity and overlap with other syndromes and diseases. A severe end of the phenotypic spectrum can be recognized as FS. This is the first report of PIGO gene mutations in a Mabry syndrome patient who also meets the criteria for FS.

50 Years Ago in TheJournal ofPediatrics: Familial Hyperphosphatasia with Mental Retardation, Seizures, and Neurologic Deficits

Mabry C, Bautista A, Kirk RFH, Dublilier LD, Braunstein H, Koepke JA. J Pediatr 1970;77:74-85. Mabry et al reported the first 4 patients with hyperphosphatasia with mental retardation syndrome (HPMRS) to present with generalized seizures and facial dysmorphism. The syndrome can be distinguished from other developmental disabilities by the stable elevation of alkaline phosphatase without bone disease.1Thompson M.D. Nezarati M.M. Gillessen-Kaesbach G. Meinecke P. Mendoza-Londono R. Mornet E. et al.Hyperphosphatasia with seizures, neurologic deficit, and characteristic facial features: five new patients with Mabry syndrome.Am J Med Genet A. 2010; 152A: 1661-1669Crossref PubMed Scopus (36) Google Scholar Few published reports of the syndrome appeared before we identified a patient whose seizures responded to pyridoxine.2Cole D.E. Thompson M.D. Neurogenic aspects of Mabry syndrome.Subcell Biochem. 2015; 76: 343-361Crossref PubMed Scopus (12) Google Scholar Improved syndromology1Thompson M.D. Nezarati M.M. Gillessen-Kaesbach G. Meinecke P. Mendoza-Londono R. Mornet E. et al.Hyperphosphatasia with seizures, neurologic deficit, and characteristic facial features: five new patients with Mabry syndrome.Am J Med Genet A. 2010; 152A: 1661-1669Crossref PubMed Scopus (36) Google Scholar made it possible to use next-generation sequencing to identify the recessive mutations that cause what became known as Mabry syndrome (OMIM 239300).2Cole D.E. Thompson M.D. Neurogenic aspects of Mabry syndrome.Subcell Biochem. 2015; 76: 343-361Crossref PubMed Scopus (12) Google Scholar There are at least 6 phenotypes. HPMRS 1, 2, 5, and 6 result from disruption of 4 genes encoding phosphatidylinositol glycan (PIG) anchor biosynthesis enzymes that act in the endoplasmic reticulum: type V (PIGV) type O (PIGO), type W (PIGW), and type Y (PIGY). HPMRS 4 and 3 result from disruption of 2 genes encoding postattachment to proteins (PGAP) enzymes that stabilize glycosylphosphatidylinositol attachment to proteins in the golgi: PGAP3 and PGAP2.3Carmody L. Blau H. Danis D. Gourdine J.-P. Vasilevsky N. Krawitz P. et al.Significantly different clinical phenotypes associated with mutations in synthesis and transamidase+remodeling glycosylphosphatidylinositol (GPI)-anchor biosynthesis genes.Orphanet J Rare Dis. 2020; 15: 40Crossref PubMed Scopus (13) Google Scholar The report by Mabry et al describes the first of at least 21 inherited glycosylphosphatidylinositol biosynthesis defects (GPIBDs) that together compose approximately 0.15% of all developmental disabilities.4Pagnamenta A.T. Murakami Y. Taylor J.M. Anzilotti C. Howard M.F. Miller V. et al.Analysis of exome data for 4293 trios suggests GPI-anchor biogenesis defects are a rare cause of developmental disorders.Eur J Hum Genet. 2017; 25: 669-679Crossref PubMed Scopus (48) Google Scholar The HPMRS3 (GPIBD8 [MIM: 614207]) phenotype presented by Mabry et al, resulting from biallelic inheritance of PGAP2 mutations, is the prototypical HPMRS phenotype among GPIBDs.5Thompson M.D. Knaus A.A. Barshop B.A. Caliebe A. Muhle H. Nguyen T.T.M. et al.A post glycosylphosphatidylinositol (GPI) attachment to proteins, type 2 (PGAP2) variant identified in Mabry syndrome index cases: Molecular genetics of the prototypical inherited GPI disorder.Eur J Med Genet. 2019; (https://www.ncbi.nlm.nih.gov/pubmed/31805394. Accessed May 15, 2020)PubMed Google Scholar This work demonstrates the value of case studies to basic science, clinical innovation, and patient follow-up.

Mabry Syndrome is a cause of hyperphosphatasia and mental retardation

Mabry Syndrome is a cause of hyperphosphatasia and mental retardation

Early infancy-onset stimulation-induced myoclonic seizures in three siblings with inherited glycosylphosphatidylinositol (GPI) anchor deficiency.

Inherited glycosylphosphatidylinositol anchor deficiency causes a variety of clinical symptoms, including epilepsy, however, little information is available regarding seizures as a symptom. We report three siblings with inherited glycosylphosphatidylinositol anchor deficiency with PIGL gene mutations. The phenotypes of the subjects were not consistent with CHIME syndrome or Mabry syndrome, as reported in previous studies. All shared some clinical manifestations, including transient apnoea as neonates, dysmorphic facial features, and intellectual disability. Between one week and 3 months of life, all patients developed myoclonic seizures. Myoclonic jerks were easily evoked by sudden unexpected acoustic or tactile stimuli. None showed elevation of serum alkaline phosphatase. Vitamin B6 was given to one of the three siblings, but failed to suppress seizures. The presence of early infancy-onset stimulation-induced myoclonic seizures combined with dysmorphic facial features should lead physicians to consider the possibility of inherited glycosylphosphatidylinositol anchor deficiency.

Perioperative Anesthetic Considerations for a Child with Mabry Syndrome

Perioperative Anesthetic Considerations for a Child with Mabry Syndrome

Phenotype-genotype correlations of PIGO deficiency with variable phenotypes from infantile lethality to mild learning difficulties.

Inherited GPI (glycosylphosphatidylinositol) deficiencies (IGDs), a recently defined group of diseases, show a broad spectrum of symptoms. Hyperphosphatasia mental retardation syndrome, also known as Mabry syndrome, is a type of IGDs. There are at least 26 genes involved in the biosynthesis and transport of GPI-anchored proteins; however, IGDs constitute a rare group of diseases, and correlations between the spectrum of symptoms and affected genes or the type of mutations have not been shown. Here, we report four newly identified and five previously described Japanese families with PIGO (phosphatidylinositol glycan anchor biosynthesis class O) deficiency. We show how the clinical severity of IGDs correlates with flow cytometric analysis of blood, functional analysis using a PIGO-deficient cell line, and the degree of hyperphosphatasia. The flow cytometric analysis and hyperphosphatasia are useful for IGD diagnosis, but the expression level of GPI-anchored proteins and the degree of hyperphosphatasia do not correlate, although functional studies do, with clinical severity. Compared with PIGA (phosphatidylinositol glycan anchor biosynthesis class A) deficiency, PIGO deficiency shows characteristic features, such as Hirschsprung disease, brachytelephalangy, and hyperphosphatasia. This report shows the precise spectrum of symptoms according to the severity of mutations and compares symptoms between different types of IGD.

Vitamin B6 related epilepsy

Vitamin B6 related epilepsy is a group of epileptic diseases, seizures in which could not be controlled by antiepileptic drugs, but could be controlled or obviously improved by vitamin B6.It comprises of pyridoxine dependent epilepsy and pyridoxine responsive epilepsy predominantly, and the latter includes vitamin B6 responsive infantile spasms, pyridox(am)ine-5′-phosphate oxidase (PNPO) deficiency, hyperphosphatasia mental retardation syndrome (Mabry syndrome) and so on.The clinical presentations of the diseases above are nonspecific, manifesting as refractory seizures onset in neonatal or infantile period, which need to be distinguished from other diseases such as newborn hypoxic ischemic encephalopathy, Ohtahara syndrome and non-ketotic hyperglycinemia.Pyridoxine dependent epilepsy, PNPO deficiency and Mabry syndrome have relative specific biomarkers and known disease-causing genes, which are helpful for diagnosis.It is suggested that pyridoxine or pyridoxal phosphate should be tried first for all patients started seizures early (including all infantile spasms patients), avoiding missing these diseases.And once diagnosed, vitamin B6 should be maintained long-term or all the life according to the detailed disease. Key words: Vitamin B6; Pyridoxine dependent epilepsy; Infantile spasms; Pyridox(am)ine-5′-phosphate oxidase deficiency; Mabry syndrome

Rare Noncoding Mutations Extend the Mutational Spectrum in the PGAP3 Subtype of Hyperphosphatasia with Mental Retardation Syndrome.

ABSTRACTHPMRS or Mabry syndrome is a heterogeneous glycosylphosphatidylinositol (GPI) anchor deficiency that is caused by an impairment of synthesis or maturation of the GPI‐anchor. The expressivity of the clinical features in HPMRS varies from severe syndromic forms with multiple organ malformations to mild nonsyndromic intellectual disability. In about half of the patients with the clinical diagnosis of HPMRS, pathogenic mutations can be identified in the coding region in one of the six genes, one among them is PGAP3. In this work, we describe a screening approach with sequence specific baits for transcripts of genes of the GPI pathway that allows the detection of functionally relevant mutations also including introns and the 5′ and 3′ UTR. By this means, we also identified pathogenic noncoding mutations, which increases the diagnostic yield for HPMRS on the basis of intellectual disability and elevated serum alkaline phosphatase. In eight affected individuals from different ethnicities, we found seven novel pathogenic mutations in PGAP3. Besides five missense mutations, we identified an intronic mutation, c.558‐10G>A, that causes an aberrant splice product and a mutation in the 3′UTR, c.*559C>T, that is associated with substantially lower mRNA levels. We show that our novel screening approach is a useful rapid detection tool for alterations in genes coding for key components of the GPI pathway.

Clinical and genetic analysis of two Chinese infants with Mabry syndrome

ObjectiveHyperphosphatasia mental retardation syndrome (Mabry syndrome) is an autosomal recessive disorder. We aim to analyze two Chinese patients diagnosed as Mabry syndrome. MethodsThe clinical manifestations, diagnosis and treatment were observed in two patients. Genetic analysis including PIGV and PIGO was examined. ResultsTwo patients were diagnosed as Mabry syndrome clinically and genetically. Developmental delay, hyperphosphatasia and seizures were presented in both of them. Typical facial dysmorphism and hypoplastic terminal phalanges were only found in one. Some novel presentations including congenital laryngeal cartilage softening, inguinal hernia, broken palmprint, optic atrophy and skeleton dysplasia such as carpal age delay and metaphysis anomalies were observed in two patients. Molecular genetic analysis revealed compound heterozygous mutations of PIGV or PIGO in our patients, including c.615C>G (p.Asn205Lys) and c.854A>G (p.Tyr285Cys) of PIGV in patient 1, and c.458T>C (p.Phe153Ser) and c.1355_1356del (p.Ala452Glyfs*52) of PIGO in patient 2. Additionally, a heterozygous c.2926G>A (Asp976Asn) of PCDH19 was identified in patient with PIGV mutations, the causative gene of Epilepsy and mental retardation limited to females (EFMR). ConclusionTo our best knowledge, this is the first time to report Chinese patients diagnosed as Mabry syndrome. For the PCDH19 mutation in our patient carrying PIGV mutations, due to lacking characteristics of EFMR and the ambiguity results in pathogenicity analysis, we were not sure how much pathogenic role PCDH19 mutation shared with PIGV mutations in this disease. The novel mutations of PIGV and PIGO, and novel clinical manifestations reported here might expand the genotype and phenotype spectrum of Mabry syndrome.

Neurogenetic Aspects of Hyperphosphatasia in Mabry Syndrome.

An autosomal recessive syndrome of hyperphosphatasia (elevated circulating alkaline phosphatase (AP), seizures and neurologic deficits) was first described by Mabry and colleagues in 1970. Over the ensuing four decades, few cases were reported. In 2010, however, new families were identified and the syndromic nature of the disorder confirmed. Shortly thereafter, next generation sequencing was used to characterize causative defects in the glycosyl phosphatidylinositol (GPI) biosynthetic pathway, based partly on our understanding of how AP is anchored by GPI to the plasma membrane. Whether the seizures and cognitive defects seen in Mabry syndrome patients are attributable in part to the constant hyperphosphatasia is not known, as there are more than 250 other proteins dependent on GPI for their anchoring to the plasma membrane. However, Mabry syndrome may provide a new window on AP function in growth and development.

8. Genetic basis of Mabry’s syndrome

We review the discovery of two genes disrupted in Mabry syndrome (hyperphosphatasia with developmental disability; OMIM#239300): a syndrome notable for characteristic facial dysmorphology (hypertelorism, a broad nasal bridge and a tented mouth); subtle hand bone abnormalities (variable shortening of middle and distal phalanges) and nerve abnormalities (plaques disrupting Schwann cells) and persistently elevated serum alkaline phosphatase (ALP). In approximately two thirds of cases, the biochemical abnormalities present in Mabry syndrome result from disruption of the phosphoinositol glycan (GPI) anchor as a result of mutations in the phosphoglycan-inositol biosynthesis type V ( PIGV ) and type O ( PIGO ) genes. The remaining one third of cases have no known mutation in the GPI anchor pathway. These idiopathic cases are reported to accumulate lysosomal storage material that has been putatively identified as a glycolipid material. As twenty genes are integral to GPI anchor synthesis, we hypothesize that idiopathic cases of Mabry syndrome may result from disruptions in other genes encoding GPI anchor biosynthesis enzymes. We are using exome sequencing and candidate gene approaches to identify the gene(s) responsible for idiopathic Mabry syndrome. This work will assist in elucidating the inborn errors of metabolism that underlie the seizures associated with Mabry syndrome.

Mutations in PGAP3 Impair GPI-Anchor Maturation, Causing a Subtype of Hyperphosphatasia with Mental Retardation

Glycosylphophatidylinositol (GPI)-anchored proteins play important roles in many biological processes, and mutations affecting proteins involved in the synthesis of the GPI anchor are reported to cause a wide spectrum of intellectual disabilities (IDs) with characteristic additional phenotypic features. Here, we describe a total of five individuals (from three unrelated families) in whom we identified mutations in PGAP3, encoding a protein that is involved in GPI-anchor maturation. Three siblings in a consanguineous Pakistani family presented with profound developmental delay, severe ID, no speech, psychomotor delay, and postnatal microcephaly. A combination of autozygosity mapping and exome sequencing identified a 13.8 Mb region harboring a homozygous c.275G>A (p.Gly92Asp) variant in PGAP3 region 17q11.2-q21.32. Subsequent testing showed elevated serum alkaline phosphatase (ALP), a GPI-anchored enzyme, in all three affected children. In two unrelated individuals in a cohort with developmental delay, ID, and elevated ALP, we identified compound-heterozygous variants c.439dupC (p.Leu147Profs(∗)16) and c.914A>G (p.Asp305Gly) and homozygous variant c.314C>G (p.Pro105Arg). The 1 bp duplication causes a frameshift and nonsense-mediated decay. Further evidence supporting pathogenicity of the missense mutations c.275G>A, c.314C>G, and c.914A>G was provided by the absence of the variants from ethnically matched controls, phylogenetic conservation, and functional studies on Chinese hamster ovary cell lines. Taken together with recent data on PGAP2, these results confirm the importance of the later GPI-anchor remodelling steps for normal neuronal development. Impairment of PGAP3 causes a subtype of hyperphosphatasia with ID, a congenital disorder of glycosylation that is also referred to as Mabry syndrome.

Inherited GPI-Anchor Deficiencies Caused By The Hypomorphic Mutations In PIG A gene: Comparison To Paroxysmal Nocturnal Hemogrobinuria

Glycosylphosphatidylinositol (GPI) is a glycolipid that anchors 150 or more kinds of proteins to the cell surface. There are at least 26 genes involved in the biosynthesis and transport of GPI anchored proteins (GPI-APs). In paroxysmal nocturnal hemogrobinuria (PNH), an acquired GPI deficiency, somatic mutation in X-linked PIGA accounts for most of the patients. A case with PNH due to a combination of inherited mutation in one allele and a somatic mutation in the other allele of autosomal gene PIGT was reported recently (Blood 2013 doi:10.1182/blood-2013-01-481499). On the other hand, many inherited GPI deficiencies (IGDs) were found recently using whole exome sequencing (Nat Genet 2010 vol.42 p827, Am J Hum Genet 2012 vol. 90 p295, p146, Am J Hum Genet 2012 vol. 91 p146, Am J Hum Genet 2013 vol. 92 p584). As the complete GPI deficiency causes embryonic death, these patients with IGD are partial deficiency. The major symptoms of IGDs include mental retardation, epilepsy, coarse facial features and multiple organ anomalies that vary in severity depending upon the degree of defect and/or position in the pathway of affected gene. We clarified a mechanism of hyperphosphatasia, an elevated release of tissue nonspecific alkaline phosphatase (TNAP, GPI-AP), seen in some of the patients with IGDs such as hyperphosphatasia mental retardation syndrome or Mabry syndrome caused by mutation in genes in the later stage of GPI biosynthesis (J Biol Chem. 2012 vol. 287 p6318)Here, we report four male patients with intellectual disabilities accompanied by seizures caused by the mutations in PIGA gene. These mutations were found by whole-exome sequencing using the Illumina HiSeq system. PIGA is X-linked gene which is involved in the first step of GPI biosynthesis pathway. These patients have germline hypomorphic mutations in PIGAgene and have completely different symptoms from patients with PNH, which is characterized by complement-mediated intravascular hemolysis.Patient 1 had a hemizygous nonsense mutation, and was diagnosed with Ohtahara syndrome (early infantile epileptic encephalopathy with suppression burst) with multiple congenital anomalies. The nonsense mutation is leaky and caused a partial deficiency. Patient 2 had a maternally inherited hemizygous missense mutation and was diagnosed with early-onset West syndrome (a severe epilepsy syndrome characterized by infantile spasm with hypsarrhythmia). Patients 3 and 4 are brothers, had maternally inherited hemizygous missense mutation and were suffering from severe intellectual disabilities with seizures but not with any anomalies. Analysis by flow cytometry of patients' blood cells revealed that all four patients showed decreased expression of GPI-APs on the granulocytes but not in erythrocytes or lymphocytes, suggesting that FACS analysis of granulocytes is useful to screen patients with IGD. Interestingly, the FACS analysis of the granulocytes from the mother of patients 3 and 4 showed mosaic pattern in CD16 expression. The mother seemed to have no neurological symptom, raising the possibility that contribution of GPI-AP-deficient cells to neuronal system does not occur or is only limited.Although PNH and IGDs are different diseases, both are partial GPI deficiencies, the former affecting only hematopoietic cells, the latter having the hypomorphic mutations, which rescue the patients from lethality but cause the severe hematopoietic and developmental abnormalities, respectively. Disclosures:No relevant conflicts of interest to declare.

Delineation of PIGV mutation spectrum and associated phenotypes in hyperphosphatasia with mental retardation syndrome

Three different genes of the glycosylphosphatidylinositol anchor synthesis pathway, PIGV, PIGO, and PGAP2, have recently been implicated in hyperphosphatasia-mental retardation syndrome (HPMRS), also known as Mabry syndrome, a rare autosomal recessive form of intellectual disability. The aim of this study was to delineate the PIGV mutation spectrum as well as the associated phenotypic spectrum in a cohort of 16 individuals diagnosed with HPMRS on the basis of intellectual disability and elevated serum alkaline phosphate as minimal diagnostic criteria. All PIGV exons and intronic boundaries were sequenced in 16 individuals. Biallelic PIGV mutations were identified in 8 of 16 unrelated families with HPMRS. The most frequent mutation detected in about 80% of affected families including the cases reported here is the c.1022C>A PIGV mutation, which was found in both the homozygous as well as the heterozygous state. Four further mutations found in this study (c. 176T>G, c.53G>A, c.905T>C, and c.1405C>T) are novel. Our findings in the largest reported cohort to date significantly extend the range of reported manifestations associated with PIGV mutations and demonstrate that the severe end of the clinical spectrum presents as a multiple congenital malformation syndrome with a high frequency of Hirschsprung disease, vesicoureteral, and renal anomalies as well as anorectal malformations. PIGV mutations are the major cause of HPMRS, which displays a broad clinical variability regarding associated malformations and growth patterns. Severe developmental delays, particular facial anomalies, brachytelephalangy, and hyperphosphatasia are consistently found in PIGV-positive individuals.

Vitamin B 6 –responsive epilepsy due to inherited GPI deficiency

Glycosylphosphatidylinositol (GPI) is a glycolipid that anchors many proteins to the cell surface. There are at least 26 genes involved in the biosynthesis of GPI-anchored proteins (GPI-APs).1 Recently, many inherited GPI deficiencies (IGDs) were found using whole-exome sequencing.2–4 The major symptoms of IGDs include mental retardation, epilepsy, coarse facial features, and multiple organ anomalies that vary in severity depending upon the degree of defect and/or position in the pathway of the affected gene. We clarified a mechanism of hyperphosphatasia, an elevated release of tissue-nonspecific alkaline phosphatase (TNAP, GPI-AP), seen in some of the patients with IGDs such as hyperphosphatasia mental retardation syndrome or Mabry syndrome caused by mutation in genes in the later stage of GPI biosynthesis.5