The spectrum of mutations in the PCFT gene, coding for an intestinal folate transporter, that are the basis for hereditary folate malabsorption

Abstract Hereditary folate malabsorption (HFM) is a rare autosomal recessive disorder caused by impaired intestinal folate absorption and impaired folate transport into the central nervous system. Recent studies in 1 family revealed that the molecular basis for this disorder is a loss-of-function mutation in the PCFT gene encoding a proton-coupled folate transporter. The current study broadens the understanding of the spectrum of alterations in the PCFT gene associated with HFM in 5 additional patients. There was no racial, ethnic, or sex pattern. A total of 4 different homozygous mutations were detected in 4 patients; 2 heterozygous mutations were identified in the fifth patient. Mutations involved 4 of the 5 exons, all at highly conserved amino acid residues. A total of 4 of the mutated transporters resulted in a complete loss of transport function, primarily due to decreased protein stability and/or defects in membrane trafficking, while 2 of the mutated carriers manifested residual function. Folate transport at low pH was markedly impaired in transformed lymphocytes from 2 patients. These findings further substantiate the role that mutations in PCFT play in the pathogenesis of HFM and will make possible rapid diagnosis and treatment of this disorder in infants, and prenatal diagnosis in families that carry a mutated gene.

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Spondylocarpotarsal synostosis syndrome due to a novel loss of function FLNB variant: a case report

BMC Musculoskeletal Disorders ◽

10.1186/s12891-020-03890-2 ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Samina Yasin ◽

Outi Makitie ◽

Sadaf Naz

Keyword(s):

Short Stature ◽

Autosomal Recessive ◽

Autosomal Recessive Disorder ◽

Loss Of Function ◽

Case Presentation ◽

Pathogenic Variants ◽

Skeletal Malformations ◽

Tarsal Bones ◽

The Family ◽

Heterozygous Carriers

Abstract Background Loss of function or gain of function variants of Filamin B (FLNB) cause recessive or dominant skeletal disorders respectively. Spondylocarpotarsal synostosis syndrome (SCT) is a rare autosomal recessive disorder characterized by short stature, fused vertebrae and fusion of carpal and tarsal bones. We present a novel FLNB homozygous pathogenic variant and present a carrier of the variant with short height. Case presentation We describe a family with five patients affected with skeletal malformations, short stature and vertebral deformities. Exome sequencing revealed a novel homozygous frameshift variant c.2911dupG p.(Ala971GlyfsTer122) in FLNB, segregating with the phenotype in the family. The variant was absent in public databases and 100 ethnically matched control chromosomes. One of the heterozygous carriers of the variant had short stature. Conclusion Our report expands the genetic spectrum of FLNB pathogenic variants. It also indicates a need to assess the heights of other carriers of FLNB recessive variants to explore a possible role in idiopathic short stature.

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Identification and functional characterisation of a novel KCNJ2 mutation, Val302del, causing Andersen–Tawil syndrome

Canadian Journal of Physiology and Pharmacology ◽

10.1139/cjpp-2014-0527 ◽

2015 ◽

Vol 93 (7) ◽

pp. 569-575 ◽

Cited By ~ 2

Author(s):

Balázs Ördög ◽

Lidia Hategan ◽

Mária Kovács ◽

György Seprényi ◽

Zsófia Kohajda ◽

...

Keyword(s):

Membrane Trafficking ◽

Genetic Disorder ◽

Clinical Manifestations ◽

Clinical Importance ◽

Inhibitory Effect ◽

Periodic Paralysis ◽

Inward Rectification ◽

Loss Of Function ◽

Gene Encoding ◽

Functional Characterisation

Loss-of-function mutations of the KCNJ2 gene encoding for the inward rectifier potassium channel subunit Kir2.1 cause Andersen–Tawil Syndrome (ATS), a rare genetic disorder characterised by periodic paralysis, ventricular arrhythmias, and dysmorphic features. Clinical manifestations of the disease appear to vary greatly with the nature of mutation, therefore, functional characterisation of ATS-causing mutations is of clinical importance. In this study, we describe the identification and functional analysis of a novel KCNJ2 mutation, Val302del, identified in a patient with ATS. Heterologously expressed wild type (WT) and Val302del mutant alleles showed similar subcellular distribution of the Kir2.1 protein with high intensity labelling from the membrane region, demonstrating normal membrane trafficking of the Val302del Kir2.1 variant. Cells transfected with the WT allele displayed a robust current with strong inward rectification, while no current above background was detected in cells expressing the Val302del Kir2.1 subunit. Co-transfection of CHO cells with the WT and the Val302del Kir2.1 revealed a dose-dependent inhibitory effect of the Val302del Kir2.1 mutant subunit on WT Kir2.1 currents. These observations indicate that the WT and the Val302del mutant subunits co-assemble in the cell membrane and that the mutation affects potassium conductivity and (or) gating of the WT/Val302del heteromeric Kir2.1 channels.

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SERKAL Syndrome: An Autosomal-Recessive Disorder Caused by a Loss-of-Function Mutation in WNT4

The American Journal of Human Genetics ◽

10.1016/j.ajhg.2007.08.005 ◽

2008 ◽

Vol 82 (1) ◽

pp. 39-47 ◽

Cited By ~ 129

Author(s):

Hannah Mandel ◽

Revital Shemer ◽

Zvi U. Borochowitz ◽

Marina Okopnik ◽

Carlos Knopf ◽

...

Keyword(s):

Autosomal Recessive ◽

Autosomal Recessive Disorder ◽

Loss Of Function

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Mutations in the ELA2 gene encoding neutrophil elastase are present in most patients with sporadic severe congenital neutropenia but only in some patients with the familial form of the disease

Blood ◽

10.1182/blood.v98.9.2645 ◽

2001 ◽

Vol 98 (9) ◽

pp. 2645-2650 ◽

Cited By ~ 87

Author(s):

Phil J. Ancliff ◽

Rosemary E. Gale ◽

Ri Liesner ◽

Ian M. Hann ◽

David C. Linch

Keyword(s):

Neutrophil Elastase ◽

Autosomal Recessive ◽

Autosomal Dominant ◽

Autosomal Recessive Disorder ◽

Severe Neutropenia ◽

Base Substitution ◽

Severe Congenital Neutropenia ◽

Congenital Neutropenia ◽

Gene Encoding ◽

Familial Form

Abstract Severe congenital neutropenia (SCN) was originally described as an autosomal recessive disorder. Subsequently, autosomal dominant and sporadic forms of the disease have been recognized. All forms are manifest by persistent severe neutropenia and recurrent bacterial infection. In contrast, cyclical hematopoiesis is characterized by periodic neutropenia inter-spaced with (near) normal neutrophil counts. Recently, linkage analysis on 13 affected pedigrees identified chromosome 19p13.3 as the likely position for mutations in cyclical hematopoiesis. Heterozygous mutations in the ELA2 gene encoding neutrophil elastase were detected in all families studied. Further work also demonstrated mutations in ELA2 in sporadic and autosomal dominant SCN. However, all mutations described to date are heterozygous and thus appear to act in a dominant fashion, which is inconsistent with an autosomal recessive disease. Therefore, the current study investigated whether mutations in ELA2could account for the disease phenotype in classical autosomal recessive SCN and in the sporadic and autosomal dominant types. All 5 exons of ELA2 and their flanking introns were studied in 18 patients (3 autosomal recessive, 5 autosomal dominant [from 3 kindreds], and 10 sporadic) using direct automated sequencing. No mutations were found in the autosomal recessive families. A point mutation was identified in 1 of 3 autosomal dominant families, and a base substitution was identified in 8 of 10 patients with the sporadic form, though 1 was subsequently shown to be a low-frequency polymorphism. These results suggest that mutations in ELA2are not responsible for classical autosomal recessive Kostmann syndrome but provide further evidence for the role of ELA2 in SCN.

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Identification of a functionally critical GXXG motif and its relationship to the folate binding site of the proton-coupled folate transporter (PCFT-SLC46A1)

AJP Cell Physiology ◽

10.1152/ajpcell.00123.2012 ◽

2012 ◽

Vol 303 (6) ◽

pp. C673-C681 ◽

Cited By ~ 25

Author(s):

Rongbao Zhao ◽

Daniel Sanghoon Shin ◽

Andras Fiser ◽

I. David Goldman

Keyword(s):

Functional Role ◽

Autosomal Recessive ◽

Structural Model ◽

Transmembrane Domain ◽

Autosomal Recessive Disorder ◽

Binding Pocket ◽

Loss Of Function ◽

Substituted Cysteine Accessibility ◽

Translocation Pathway

The proton-coupled folate transporter (PCFT) mediates intestinal folate absorption, and loss-of-function mutations in this gene result in the autosomal recessive disorder hereditary folate malabsorption. The current study, focused on a structure-functional analysis of this transporter, identified Gly-189 and Gly-192 (a GxxG motif) located in the fifth transmembrane domain as residues that could not be replaced with alanine without a loss of function. In contrast, function was preserved when Gly-56 and Gly-59 (the other conservative GXXG motif in human PCFT) were replaced with alanine. Similarly, Gly-93 and Gly-97, which constitute the only conserved GXXXG dimerization motif in human PCFT, tolerated alanine substitution. To explore the role of this region in folate binding, the residues around Gly-189 and Gly-192 were analyzed by the substituted cysteine accessibility method. Both I188C and M193C mutants were functional and were inhibited by membrane-impermeable sulfhydryl-reactive reagents; this could be prevented with PCFT substrate, but the protection was sustained at 0°C only for the I188C mutant, consistent with localization of Ile-188 in the PCFT folate binding pocket. The functional role of residues around Gly-189 and Gly-192 is consistent with a molecular structural model in which these two residues along with Ieu-188 are accessible to the PCFT aqueous translocation pathway.

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Meckel-Gruber syndrome: Report of two cases

Journal of Neurosciences in Rural Practice ◽

10.4103/0976-3147.91943 ◽

2012 ◽

Vol 03 (01) ◽

pp. 56-59 ◽

Cited By ~ 4

Author(s):

C. Panduranga ◽

Ranjit Kangle ◽

Rajshree Badami ◽

Prakash V Patil

Keyword(s):

Central Nervous System ◽

Nervous System ◽

Autosomal Recessive ◽

Renal Cysts ◽

Autosomal Recessive Disorder ◽

Finnish Population ◽

Developmental Anomalies ◽

Rare Syndrome ◽

The Central Nervous System ◽

Syndrome Report

ABSTRACTMeckel-Gruber syndrome (MKS) is an autosomal recessive disorder, characterized by a combination of renal cysts and variably associated with features including developmental anomalies of the central nervous system (typically encephalocele), hepatic ductal dysplasia, cysts, and polydactyly. It is a rare syndrome with highest incidence in Gujarati Indians and Finnish population. We report two such cases of MKS in non-Gujarati Indian which were diagnosed by neonatal autopsy.

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PRKG2 Splice Site Variant in Dogo Argentino Dogs with Disproportionate Dwarfism

Genes ◽

10.3390/genes12101489 ◽

2021 ◽

Vol 12 (10) ◽

pp. 1489

Author(s):

Gabriela Rudd Garces ◽

Maria Elena Turba ◽

Myriam Muracchini ◽

Alessia Diana ◽

Vidhya Jagannathan ◽

...

Keyword(s):

Autosomal Recessive ◽

Donor Site ◽

Genetic Defect ◽

Autosomal Recessive Inheritance ◽

Homozygosity Mapping ◽

Splice Donor Site ◽

Loss Of Function ◽

Gene Encoding ◽

Encoding Protein

Dwarfism phenotypes occur in many species and may be caused by genetic or environmental factors. In this study, we investigated a family of nine Dogo Argentino dogs, in which two dogs were affected by disproportionate dwarfism. Radiographs of an affected dog revealed a decreased level of endochondral ossification in its growth plates, and a premature closure of the distal ulnar physes. The pedigree of the dogs presented evidence of monogenic autosomal recessive inheritance; combined linkage and homozygosity mapping assigned the most likely position of a potential genetic defect to 34 genome segments, totaling 125 Mb. The genome of an affected dog was sequenced and compared to 795 control genomes. The prioritization of private variants revealed a clear top candidate variant for the observed dwarfism. This variant, PRKG2:XM_022413533.1:c.1634 + 1G>T, affects the splice donor site and is therefore predicted to disrupt the function of the PKRG2 gene encoding protein, kinase cGMP-dependent type 2, a known regulator of chondrocyte differentiation. The genotypes of the PRKG2 variant were perfectly associated with the phenotype in the studied family of dogs. PRKG2 loss-of-function variants were previously reported to cause disproportionate dwarfism in humans, cattle, mice, and rats. Together with the comparative data from other species, our data strongly suggest PRKG2:c.1634+1G>T to be a candidate causative variant for the observed dwarfism phenotype in Dogo Argentino dogs.

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A Novel Mutation in the VPS13B Gene in a Cohen Syndrome Patient with Positive Antiphospholipid Antibodies

Case Reports in Immunology ◽

10.1155/2021/3143609 ◽

2021 ◽

Vol 2021 ◽

pp. 1-3

Author(s):

Roghayeh Dehghan ◽

Mahdiyeh Behnam ◽

Alireza Moafi ◽

Mansoor Salehi

Keyword(s):

Antiphospholipid Antibodies ◽

Autosomal Recessive ◽

Novel Mutation ◽

Mental Deficiency ◽

Autosomal Recessive Disorder ◽

Facial Features ◽

Loss Of Function ◽

Cohen Syndrome ◽

Mild Anemia ◽

Homozygous Nonsense Mutation

Cohen syndrome is an autosomal recessive disorder with the primary symptoms of mental deficiency, progressive retinopathy, hypotonia, microcephaly, obesity of midchildhood onset, intermittent neutropenia, and dysmorphic facial features. The syndrome has high phenotypic heterogeneity and is caused by loss-of-function mutations in the VPS13B gene. Here, we introduce a novel homozygous nonsense mutation (c.8698G > T, p.E2900X) in the VPS13B gene in an 11-year-old Iranian boy with major symptoms of Cohen syndrome. He also had mild anemia accompanied by positive antiphospholipid antibodies, the latter has never been previously reported in Cohen syndrome.

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Autosomal Recessive Disorder Otospondylomegaepiphyseal Dysplasia Is Associated with Loss-of-Function Mutations in the COL11A2 Gene

The American Journal of Human Genetics ◽

10.1086/302750 ◽

2000 ◽

Vol 66 (2) ◽

pp. 368-377 ◽

Cited By ~ 53

Author(s):

Miia Melkoniemi ◽

Han G. Brunner ◽

Sylvie Manouvrier ◽

Raoul Hennekam ◽

Andrea Superti-Furga ◽

...

Keyword(s):

Autosomal Recessive ◽

Autosomal Recessive Disorder ◽

Loss Of Function ◽

Col11a2 Gene

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Role of the glutamate 185 residue in proton translocation mediated by the proton-coupled folate transporter SLC46A1

AJP Cell Physiology ◽

10.1152/ajpcell.00096.2009 ◽

2009 ◽

Vol 297 (1) ◽

pp. C66-C74 ◽

Cited By ~ 38

Author(s):

Ersin Selcuk Unal ◽

Rongbao Zhao ◽

I. David Goldman

Keyword(s):

Proton Translocation ◽

Amino Acid Residues ◽

Loss Of Function ◽

Wild Type ◽

Folate Transport ◽

Rate Limiting Step ◽

Proximal Small Intestine ◽

Transport Cycle ◽

Rate Limiting

The proton-coupled folate transporter (PCFT) SLC46A1 mediates uphill folate transport into enterocytes in proximal small intestine coupled to the inwardly directed proton gradient. Hereditary folate malabsorption is due to loss-of-function mutations in the PCFT gene. This study addresses the functional role of conserved charged amino acid residues within PCFT transmembrane domains with a detailed analysis of the PCFT E185 residue. D156A-, E185A-, E232A-, R148A-, and R376A-PCFT mutants lost function at pH 5.5, as assessed by transient transfection in folate transport-deficient HeLa cells. At pH 7.4, function was preserved only for E185A-PCFT. Loss of function for E185A-PCFT at pH 5.5 was due to an eightfold decrease in the [3H]methotrexate (MTX) influx Vmax; the MTX influx Ktwas identical to that of wild-type (WT)-PCFT (1.5 μM). Consistent with the intrinsic functionality of E185A-PCFT, [3H]MTX influx at pH 5.5 or 7.4 was trans-stimulated in cells preloaded with nonlabeled MTX or 5-formyltetrahydrofolate. Replacement of E185 with Leu, Cys, His, or Gln resulted in a phenotype similar to E185A-PCFT. However, there was greater preservation of activity (∼38% of WT) for the similarly charged E185D-PCFT at pH 5.5. All E185 substitution mutants were biotin accessible at the plasma membrane at a level comparable to WT-PCFT. These observations suggest that the E185 residue plays an important role in the coupled flows of protons and folate mediated by PCFT. Coupling appears to have a profound effect on the maximum rate of transport, consistent with augmentation of a rate-limiting step in the PCFT transport cycle.

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