A case of inherited glycosylphosphatidylinositol deficiency caused by PGAP3 variant with uniparental isodisomy on chromosome 17.

BACKGROUND: Inherited glycosylphosphatidylinositol (GPI) deficiency is an autosomal recessive disease and a set of syndromes caused by different genes involved in the biosynthesis of phosphatidylinositol characterized by severe cognitive disability, elevated serum alkaline phosphatase (ALP) levels, and distinct facial features. This report presents a patient with inherited GPI deficiency caused by a homozygous frameshift variant of PGAP3 due to uniparental isodisomy (UPiD) on chromosome 17. METHOD: Clinical characteristics of the patient were collected. Microarray analysis followed by adaptive sampling sequencing targeting chromosome 17 was used for the identification of variants. Sanger sequencing was used to confirm the variant in the target region. RESULTS: The patient was born at 38 weeks of gestation with a birthweight of 3893 g. He had a distinctive facial appearance with hypertelorism, wide nasal bridge, and cleft soft palate. Postnatal head magnetic resonance imaging revealed a Blake's pouch cyst. The serum ALP level was 940 IU/L at birth and increased to 1781 IU/L at 28 days of age. Microarray analysis revealed region of homozygosity in nearly the entire region of chromosome 17, leading to the diagnosis of UPiD. Adaptive sampling sequencing targeting chromosome 17 confirmed the homozygous variant NM_033419:c.778dupG (p.Val260Glyfs*14) in the PGAP3 gene, resulting in a diagnosis of inherited GPI deficiency. CONCLUSION: This is the first report of inherited GPI deficiency caused by UPiD. Inherited GPI deficiency must be considered in patients with unexplained hyperphosphatasemia.

Family analysis and literature study of hereditary hypophosphatemic rickets with hypercalciuria.

BACKGROUND: Hereditary hypophosphatemia rickets with hypercalciuria (HHRH) is a rare autosomal recessive disorder characterised by reduced renal phosphate reabsorption leading to hypophosphataemia, rickets and bone pain. Here, we present a case of HHRH in a Chinese boy. CASE PRESENTATION: We report a 11-year-old female proband, who was admitted to our hospital with bilateral genuvarum deformity and short stature. Computed Tomography (CT) showed kidney stones, blood tests showed hypophosphatemia, For a clear diagnosis, we employed high-throughput sequencing technology to screen for variants. Our gene sequencing approach encompassed whole exome sequencing, detection of exon and intron junction regions, and examination of a 20 bp region of adjacent introns. Flanking sequences are defined as ±50 bp upstream and downstream of the 5' and 3' ends of the coding region.The raw sequence data were compared to the known gene sequence data in publicly available sequence data bases using Burrows-Wheeler Aligner software (BWA, 0.7.12-r1039), and the pathogenic variant sites were annotated using Annovar. Subsequently, the suspected pathogenic variants were classified according to ACMG's gene variation classification system. Simultaneously, unreported or clinically ambiguous pathogenic variants were predicted and annotated based on population databases. Any suspected pathogenic variants identified through this analysis were then validated using Sanger sequencing technology. At last, the proband and her affected sister carried pathogenic homozygous variant in the geneSLC34A3(exon 13, c.1402C > T; p.R468W). Their parents were both heterozygous carriers of the variant. Genetic testing revealed that the patient has anLRP5(exon 18, c.3917C > T; p.A1306V) variant of Uncertain significance, which is a rare homozygous variant. CONCLUSION: This case report aims to raise awareness of the presenting characteristics of HHRH. The paper describes a unique case involving variants in both theSLC34A3andLRP5genes, which are inherited in an autosomal recessive manner. This combination of gene variants has not been previously reported in the literature. It is uncertain whether the presence of these two mutated genes in the same individual will result in more severe clinical symptoms. This report shows that an accurate diagnosis is critical, and with early diagnosis and correct treatment, patients will have a better prognosis.

The Molecular Basis of Calcium and Phosphorus Inherited Metabolic Disorders.

Calcium (Ca) and Phosphorus (P) hold a leading part in many skeletal and extra-skeletal biological processes. Their tight normal range in serum mirrors their critical role in human well-being. The signalling "voyage" starts at Calcium Sensing Receptor (CaSR) localized on the surface of the parathyroid glands, which captures the "oscillations" of extracellular ionized Ca and transfers the signal downstream. Parathyroid hormone (PTH), Vitamin D, Fibroblast Growth Factor (FGF23) and other receptors or ion-transporters, work synergistically and establish a highly regulated signalling circuit between the bone, kidneys, and intestine to ensure the maintenance of Ca and P homeostasis. Any deviation from this well-orchestrated scheme may result in mild or severe pathologies expressed by biochemical and/or clinical features. Inherited disorders of Ca and P metabolism are rare. However, delayed diagnosis or misdiagnosis may cost patient's quality of life or even life expectancy. Unravelling the thread of the molecular pathways involving Ca and P signaling, we can better understand the link between genetic alterations and biochemical and/or clinical phenotypes and help in diagnosis and early therapeutic intervention.

Validation of a next-generation sequencing (NGS) panel to improve the diagnosis of X-linked hypophosphataemia (XLH) and other genetic disorders of renal phosphate wasting.

BACKGROUND: Hypophosphataemic rickets (HR) comprise a clinically and genetically heterogeneous group of conditions, defined by renal-tubular phosphate wasting and consecutive loss of bone mineralisation. X-linked hypophosphataemia (XLH) is the most common form, caused by inactivating dominant mutations in PHEX, a gene encompassing 22 exons located at Xp22.1. XLH is treatable by anti-Fibroblast Growth Factor 23 antibody, while for other forms of HR such as therapy may not be indicated. Therefore, a genetic differentiation of HR is recommended. OBJECTIVE: To develop and validate a next-generation sequencing panel for HR with special focus on PHEX. DESIGN AND METHODS: We designed an AmpliSeq gene panel for the IonTorrent PGM next-generation platform for PHEX and ten other HR-related genes. For validation of PHEX sequencing 50 DNA-samples from XLH-patients, in whom 42 different mutations in PHEX and 1 structural variation have been proven before, were blinded, anonymised and investigated with the NGS panel. In addition, we analyzed one known homozygous DMP1 mutation and two samples of HR-patients, where no pathogenic PHEX mutation had been detected by conventional sequencing. RESULTS: The panel detected all 42 pathogenic missense/nonsense/splice-site/indel PHEX-mutations and in one the known homozygous DMP1 mutation. In the remaining two patients, we revealed a somatic mosaicism of a PHEX mutation in one; as well as two variations in DMP1 and a very rare compound heterozygous variation in ENPP1 in the second patient. CONCLUSIONS: This developed NGS panel is a reliable tool with high sensitivity and specificity for the diagnosis of XLH and related forms of HR.

Hyperphosphatasia with mental retardation syndrome type 4 in three unrelated South African patients.

Hyperphosphatasia with mental retardation syndrome (HPMRS) is a rare autosomal recessive disorder caused by pathogenic variants in genes involved in glycosylphosphatidylinositol metabolism that result in a similar phenotype. We describe the first three patients with HPMRS from sub-Saharan Africa. Detection was assisted by Face2Gene phenotype matching and confirmed by the presence of elevated serum alkaline phosphatase. All three patients had severe intellectual disability, absent speech, hypotonia and palatal abnormality (cleft palate in two, very high-arched palate in one), no or minimal brachytelephalangy, and high serum alkaline phosphatase levels. Additional findings included seizures in two, and brain imaging abnormalities in two. In all three patients HPMRS was a top-20 gestalt match using Face2Gene. The overall phenotype is consistent with descriptions in the literature of HPMRS type 4, although not specific to it. Whole exome sequencing in the index patient and his mother detected a candidate variant in a homozygous state in the index patient (PGAP3:c.557G>C, p.Arg186Thr) and heterozygous in the mother. Further variant interpretation indicated pathogenicity. Sanger sequencing of another two patients identified the same homozygous, pathogenic variant, confirming a diagnosis of HPMRS type 4. The shared homozygous variant in apparently unrelated families, and in the absence of consanguinity, suggests the possibility of genetic drift due to a population bottleneck effect, and further research is recommended.

PGAP3 Associated with Hyperphosphatasia with Mental Retardation Plays a Novel Role in Brain Morphogenesis and Neuronal Wiring at Early Development.

Recessive mutations in Post-GPI attachment to proteins 3 (PGAP3) cause the rare neurological disorder hyperphosphatasia with mental retardation syndrome 4 type (HPMRS4). Here, we report a novel homozygous nonsense mutation in PGAP3 (c.265C>T-p.Gln89*), in a 3-year-old boy with unique novel clinical features. These include decreased intrauterine fetal movements, dysgenesis of the corpus callosum, olfactory bulb agenesis, dysmorphic features, cleft palate, left ear constriction, global developmental delay, and hypotonia. The zebrafish functional modeling of PGAP3 loss resulted in HPMRS4-like features, including structural brain abnormalities, dysmorphic cranial and facial features, hypotonia, and seizure-like behavior. Remarkably, morphants displayed defective neural tube formation during the early stages of nervous system development, affecting brain morphogenesis. The significant aberrant midbrain and hindbrain formation demonstrated by separation of the left and right tectal ventricles, defects in the cerebellar corpus, and caudal hindbrain formation disrupted oligodendrocytes expression leading to shorter motor neurons axons. Assessment of zebrafish neuromuscular responses revealed epileptic-like movements at early development, followed by seizure-like behavior, loss of touch response, and hypotonia, mimicking the clinical phenotype human patients. Altogether, we report a novel pathogenic PGAP3 variant associated with unique phenotypic hallmarks, which may be related to the gene's novel role in brain morphogenesis and neuronal wiring.

Physiology of FGF23 and overview of genetic diseases associated with renal phosphate wasting.

Phosphate is a cornerstone of several physiological pathways including skeletal development, bone mineralization, membrane composition, nucleotide structure, maintenance of plasma pH, and cellular signaling. The kidneys have a key role in phosphate homeostasis with three hormones having important functions in renal phosphate handling or intestinal absorption: parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and 1-25-dihydroxyvitamin D (1,25(OH)2D). FGF23 is mainly synthesized by osteocytes; it is a direct phosphaturic factor that also inhibits 1,25(OH)2D and PTH. In addition to crucial effects on phosphate and calcium metabolism, FGF23 also has 'off-target' effects notably on the cardiovascular, immune and central nervous systems. Genetic diseases may affect the FGF23 pathway, resulting in either increased FGF23 levels leading to hypophosphatemia (such as in X-linked hypophosphatemia) or defective secretion/action of intact FGF23 inducing hyperphosphatemia (such as in familial tumoral calcinosis). The aim of this review is to provide an overview of FGF23 physiology and pathophysiology in X-linked hypophosphatemia, with a focus on FGF23-associated genetic diseases.

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.

We report that recessive inheritance of a post-GPI attachment to proteins 2 (PGAP2) gene variant results in the hyperphosphatasia with neurologic deficit (HPMRS) phenotype described by Mabry et al., in 1970. HPMRS, or Mabry syndrome, is now known to be one of 21 inherited glycosylphosphatidylinositol (GPI) deficiencies (IGDs), or GPI biosynthesis defects (GPIBDs). Bi-allelic mutations in at least six genes result in HPMRS phenotypes. Disruption of four phosphatidylinositol glycan (PIG) biosynthesis genes, PIGV, PIGO, PIGW and PIGY, expressed in the endoplasmic reticulum, result in HPMRS 1, 2, 5 and 6; disruption of the PGAP2 and PGAP3 genes, necessary for stabilizing the association of GPI anchored proteins (AP) with the Golgi membrane, result in HPMRS 3 and 4. We used exome sequencing to identify a novel homozygous missense PGAP2 variant NM_014489.3:c.881C > T, p.Thr294Met in two index patients and targeted sequencing to identify this variant in an unrelated patient. Rescue assays were conducted in two PGAP2 deficient cell lines, PGAP2 KO cells generated by CRISPR/Cas9 and PGAP2 deficient CHO cells, in order to examine the pathogenicity of the PGAP2 variant. First, we used the CHO rescue assay to establish that the wild type PGAP2 isoform 1, translated from transcript 1, is less active than the wild type PGAP2 isoform 8, translated from transcript 12 (alternatively spliced to omit exon 3). As a result, in our variant rescue assays, we used the more active NM_001256240.2:c.698C > T, p.Thr233Met isoform 8 instead of NM_014489.3:c.881C > T, p.Thr294Met isoform 1. Flow cytometric analysis showed that restoration of cell surface CD59 and CD55 with variant PGAP2 isoform 8, driven by the weak (pTA FLAG) promoter, was less efficient than wild type isoform 8. Therefore, we conclude that recessive inheritance of c.881C > T PGAP2, expressed as the hypomorphic PGAP2 c.698C > T, p.Thr233Met isoform 8, results in prototypical Mabry phenotype, HPMRS3 (GPIBD 8 [MIM: 614207]). This study highlights the need for long-term follow up of individuals with rare diseases in order to ensure that they benefit from innovations in diagnosis and treatment.

Expanding the phenotypic spectrum of Mabry Syndrome with novel PIGO gene variants associated with hyperphosphatasia, intractable epilepsy, and complex gastrointestinal and urogenital malformations.

Mabry syndrome is a glycophosphatidylinositol (GPI) deficiency characterized by intellectual disability, distinctive facial features, intractable seizures, and hyperphosphatasia. We expand the phenotypic spectrum of inherited GPI deficiencies with novel bi-allelic phosphatidylinositol glycan anchor biosynthesis class O (PIGO) variants in a neonate who presented with intractable epilepsy and complex gastrointestinal and urogenital malformations.

Clinical, genetic, and molecular characterization of hyperphosphatasia with mental retardation: a case report and literature review.

BACKGROUND: Hyperphosphatasia with mental retardation syndrome (HPMRS) is a recessive disorder characterized by high blood levels of alkaline phosphatase together with typical dysmorphic signs such as cleft palate, intellectual disability, cardiac abnormalities, and developmental delay. Genes involved in the glycosylphosphatidylinositol pathway and known to be mutated in HPMRS have never been characterized in the Lebanese population. CASE PRESENTATION: Herein, we describe a pair of monozygotic twins presenting with severe intellectual disability, distinct facial dysmorphism, developmental delay, and increased alkaline phosphatase level. Two individuals underwent whole exome sequencing followed by Sanger sequencing to confirm the co-segregation of the mutation in the consanguineous family. A biallelic loss of function mutation in PGAP3 was detected. Both patients were homozygous for the c.203delC (p.C68LfsX88) mutation and the parents were carriers confirming the founder effect of the mutation. High ALP serum levels confirmed the molecular diagnosis. CONCLUSION: Our findings have illustrated the genomic profile of PGAP3-related HPMRS which is essential for targeted molecular and genetic testing. Moreover, we found previously unreported clinical findings such as hypodontia and skin hyperpigmentation. These features, together with the novel mutation expand the phenotypic and genotypic spectrum of this rare recessive disorder.

Mutations in the PIGW gene associated with hyperphosphatasia and mental retardation syndrome: a case report.

BACKGROUND: Mutations in the PIGV, PIGO, PIGL, PIGY, PGAP2, PGAP3, and PIGW genes have recently been reported to cause hyperphosphatasia accompanied by mental retardation syndrome (HPMRS); the latter is an autosomal-recessive neurological disorder typically characterised by recurrent seizures, intellectual disability, and distinct facial features. Here, we report an extremely rare case of a Chinese boy with compound heterozygous PIGW mutations who suffers from severe pneumonia, mental retardation, and epilepsy. CASE PRESENTATION: A 70-day-old boy presented with fever and cough over 20 days in duration at the time of admission. At the age of 6 months, unusual facial features were apparent, and seizures were clinically observed, accompanied by obvious cognitive delay. Next-generation sequencing identified novel PIGW c.178G > A and c.462A > T mutations, confirmed by Sanger sequencing. CONCLUSIONS: Mutations in the PIGW gene in infants can cause various symptoms and multiple anomalies. Next-generation sequencing efficiently detects such mutations. The compound PIGW mutations that we describe expand the genotype/phenotype spectrum of HPMRS and may aid in clinical treatment.

Hyperphosphatasia with mental retardation syndrome type 4 In two siblings-expanding the phenotypic and mutational spectrum.

Hyperphosphatasia with mental retardation syndrome (HPMRS) (OMIM # 239300), is an autosomal recessive disease with phenotypic variability, ranging from mild nonsyndromic intellectual disability to syndromic form with severe intellectual disability, seizures, elevated alkaline phosphatase, brachytelephalangy and facial dysmorphism, Six subgroups of HPMRS were defined in which pathogenic mutations affect genes involved in either synthesis or remodeling of the anchor proteins. Among these, PGAP3 mutations are associated with HPMRS type 4. We report two siblings with a novel homozygous variant in PGAP3 expanding both the phenotypic findings and the mutational spectrum of HPMRS type 4. Developmental delay, hypotonia, facial dysmorphism were the consistent findings with HPMRS in our patients. Large anterior fontanel size, gum hypertrophy, pes equinovarus, concentric ventricle hypertrophy, frontoparietal atrophy and dysphagia were the findings of our patients that have been reported for the first time in this syndrome. Although there is an extensive list of differential diagnoses in patients with developmental delay and hypotonia, the recognizable pattern of facial features, parental consanguinity and mild to moderate serum ALP elevation should be sufficiently suggestive of HPMRS type 4.

Association of klotho gene polymorphism and the regulation of calcium-phosphate metabolism disorders in patients with end-stage renal disease.

BACKGROUND: Klotho G-395-A gene polymorphism is associated with several diseases; however, its association with calcium-phosphate metabolism disorders in end-stage renal disease (ESRD) is unknown. METHODS: A total of 137 patients with ESRD and 80 healthy adults (control) were enrolled in the study. Patients with ESRD were divided into three subgroups: haemodialysis (A1, n = 52), peritoneal dialysis (A2, n = 30), and non-dialysis (A3, n = 55). The klotho G-395-A genotype was detected by TaqMan PCR assay, and ELISA was used to detect the soluble klotho protein (sKL) and fibroblast growth factor (FGF23). Intact parathyroid hormone (iPTH) and other related clinical biochemical parameters were also analyzed for all subjects. RESULTS: (i) Three genotypes (GG, GA and AA) of KL G-395A were detected, and a significant difference between the ESRD and control groups was observed, (ii) sKL was inversely associated with FGF23 in each subgroup and phosphate and positively associated with calcium in A1 and A3. FGF23 was positively associated with phosphate and inversely associated with calcium in each subgroup, (iii) a statistical difference in levels of sKL and FGF23 was observed between GG and AA, as well as between GA and AA. The expression of sKL was lowest and the level of FGF23 was highest in AA and (iv). GA + AA genotypes and FGF23 were risk factors and sKL might be protective factor of calcium-phosphate metabolism disorders. CONCLUSION: Soluble klotho protein and FGF23 were associated with the regulation of calcium and phosphate metabolism, and the A allele of the G-395A klotho gene polymorphism could be a risk factor on calcium-phosphate metabolism disorders in patients with ESRD.

Phosphate homeostasis disorders.

Our understanding of the regulation of phosphate balance has benefited tremendously from the molecular identification and characterization of genetic defects leading to a number of rare inherited or acquired disorders affecting phosphate homeostasis. The identification of the key phosphate-regulating hormone, fibroblast growth factor 23 (FGF23), as well as other molecules that control its production, such as the glycosyltransferase GALNT3, the endopeptidase PHEX, and the matrix protein DMP1, and molecules that function as downstream effectors of FGF23 such as the longevity factor Klotho and the phosphate transporters NPT2a and NPT2c, has permitted us to understand the complex interplay that exists between the kidneys, bone, parathyroid, and gut. Such insights from genetic disorders have allowed not only the design of potent targeted treatment of FGF23-dependent hypophosphatemic conditions, but also provide clinically relevant observations related to the dysregulation of mineral ion homeostasis in health and disease.

Delineating the phenotypic spectrum of hyperphosphatasia with mental retardation syndrome 4 in 14 patients of Middle-Eastern origin.

Hyperphosphatasia with mental retardation syndrome 4 (HPMRS4) is a rare autosomal recessive condition caused by an impairment of glycosylphophatidylinositol biosynthesis. The cardinal features of HPMRS4 include; characteristic facial features, severe intellectual disability and various neurologic abnormalities. We report here detailed clinical, biochemical, and molecular findings of 14 patients clinically suspected to have HPMRS4, from three Middle-Eastern Countries; Saudi Arabia, Qatar, and Oman. All patients in our series presented with the cardinal features pointing to HPMRS4 and with an elevated alkaline phosphatase level. Five patients had megalocornea, which have been reported recently in an Arab patient. Additionally, fracture, bilateral coxa valga, camptodactyly, truncal obesity, and hyperpigmented macules of the upper thigh, each was seen once and was not described before with HPMRS4. Additional clinical and radiological findings are described, supporting the novel clinical and radiological findings recently described in Egyptian patients. The utilization of homozygosity mapping coupled with PGAP3 sequencing and whole exome sequencing facilitated the mutation detection in these patients. These missense mutations include c.320C > T (p.S107 L), c.850C > T (p.H284Y), and c.851A > G (p.H284R) in the PGAP3 gene. We believe that the recurrent mutations identified in our cohort may represent founder mutations in big tribes from a certain geographical region of Saudi Arabia, Qatar, and Oman. Therefore, in case of a clinical suspicion of HPMRS4 in these populations, targeted genetic testing for the identified mutations should be performed first to expedite the genetic diagnosis.

Mabry Syndrome in a Child of South Asian Descent.

Mabry syndrome is the triad of seizures, hyperphosphatasia, and mental disability. It usually manifests in first year of life and has an autosomal recessive mode of inheritance. Besides the usual triad, other manifestations of Mabry syndrome include hypoplasia of distal phalanges, brachytelencepahly, gastrointestinal malformations and constipation, hypertelorism, short nose with a broad nasal bridge and dip, and thin upper lip with down turned corners of the mouth. More than 20 cases of Mabry syndrome have been reported in medical literature. Herein, we report the case of a six-month child with Mabry syndrome that presented with decreased neck holding, hypotonia and delayed motor milestones. The child also had a high-arched palate and hyperplastic malar eminences. Constipation was present but had a delayed onset, starting at 19 months of age. This is the first case of Mabry syndrome occurring in a child of South Asian descent.

PGAP3-related hyperphosphatasia with mental retardation syndrome: Report of 10 new patients and a homozygous founder mutation.

BACKGROUND: Hyperphosphatasia with mental retardation syndrome (HPMRS) is caused by recessive mutations in genes involved in the glycosylphosphatidylinsitol pathway, including PGAP3. MATERIALS AND METHODS: We describe 10 patients from 8 Egyptian families presenting with developmental delay, severe intellectual disability, distinct facial dysmorphism and increased alkaline phosphatase. Sanger sequencing of PGAP3 was performed. RESULTS: Eight patients had cleft palate, 4 had postnatal microcephaly and 5 had seizures. Neuro-imaging findings showed thin corpus callosum in 9 patients, mild ventriculomegaly in 3 patients and variable degrees of cerebellar vermis hypoplasia in 4 patients, a finding not previously reported in patients with HPMRS. Additional manifestations included double row teeth, hypogenitalism and congenital heart disease. Biallelic loss of function mutations in the PGAP3 gene were detected in all patients. Nine patients were homozygous for the c.402dupC (p.M135Hfs*28) mutation strongly suggesting a founder effect. On the other hand, 1 patient had a novel mutation, c.817_820delGACT (p.D273Sfs*37). CONCLUSION: This is the largest series of patients with HPMRS from same ethnic group. Our results reinforce the distinct clinical and facial features of PGAP3-related HPMRS which are the clue for targeted genetic testing. Moreover, we present additional unreported clinical and neuro-imaging findings and a novel mutation thus expanding the phenotypic and mutational spectrum of this rare disorder.

A Rare Variant in PGAP2 Causes Autosomal Recessive Hyperphosphatasia with Mental Retardation Syndrome, with a Mild Phenotype in Heterozygous Carriers.

Mutations in genes involved in the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor cause autosomal recessive glycosylation defects, with a wide phenotypic spectrum of intellectual disability, seizures, minor facial dysmorphism, hypotonia, and elevated serum alkaline phosphatase. We now describe consanguineous Bedouin kindred presenting with an autosomal recessive syndrome of intellectual disability and elevated serum alkaline phosphatase. Genome-wide linkage analysis identified 6 possible disease-associated loci. Whole-exome sequencing followed by Sanger sequencing validation identified a single variant in PGAP2 as the disease-causing mutation (C.554G>A; p.185(R>Q)), segregating as expected within the kindred and not found in 150 Bedouin controls. The mutation replaces a highly conserved arginine residue with glutamine within the Frag1 (FGF receptor activating) domain of PGAP2. Interestingly, this mutation is a known dbSNP variant (rs745521288, build 147) with a very low allele frequency (0.00000824 in dbSNP, no homozygotes reported), highlighting the fact that dbSNP variants should not be automatically ruled out as disease-causing mutations. We further showed that PGAP2 is ubiquitously expressed, but in line with the disease phenotype, it is highly transcribed in human brain, skeletal muscle, and liver. Interestingly, a mild phenotype of slightly elevated serum levels of alkaline phosphatase and significant learning disabilities was observed in heterozygous carriers.

Clinical and genetic analysis of two Chinese infants with Mabry syndrome.

OBJECTIVE: Hyperphosphatasia mental retardation syndrome (Mabry syndrome) is an autosomal recessive disorder. We aim to analyze two Chinese patients diagnosed as Mabry syndrome. METHODS: The clinical manifestations, diagnosis and treatment were observed in two patients. Genetic analysis including PIGV and PIGO was examined. RESULTS: Two 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). CONCLUSION: To 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.

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

HPMRS 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.