Publications by authors named "Noel Edwards"

17 Publications

  • Page 1 of 1

Case Report: Investigation and molecular genetic diagnosis of familial hypomagnesaemia.

F1000Res 2019 15;8:666. Epub 2019 May 15.

Renal Services, The Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, NE7 7DN, UK.

Genetic mutations causing familial hypomagnesaemia syndromes are well-recognised.  Affected patients can present with severe symptoms of hypomagnesaemia, such as seizures or cardiac arrhythmia.  We report an affected child, from a consanguineous family, who presented in the first weeks of life with seizures secondary to hypomagnesaemia, without other associated clinical features.  We performed whole exome sequencing in the affected child and segregation analysis within the family, which revealed a novel homozygous missense mutation in , which was confirmed as a heterozygous allele in both parents and two younger siblings who had transient hypomagnesaemia. Using modelling, we provide evidence that the missense variant p.(K1098E) in is pathogenic, as it disrupts stabilising TRP domain interactions. Management of familial hypomagnesaemia relies on prompt recognition, early magnesium replacement and lifelong monitoring.
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http://dx.doi.org/10.12688/f1000research.19006.2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6694456PMC
June 2020

Molecular genetic investigations identify new clinical phenotypes associated with BCS1L-related mitochondrial disease.

Hum Mol Genet 2019 11;28(22):3766-3776

Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne NE1 3BZ, UK.

BCS1L encodes a homolog of the Saccharomyces cerevisiae bcs1 protein, which has a known role in the assembly of Complex III of the mitochondrial respiratory chain. Phenotypes reported in association with pathogenic BCS1L variants include growth retardation, aminoaciduria, cholestasis, iron overload, lactic acidosis and early death (GRACILE syndrome), and Björnstad syndrome, characterized by abnormal flattening and twisting of hair shafts (pili torti) and hearing problems. Here we describe two patients harbouring biallelic variants in BCS1L; the first with a heterozygous variant c.166C>T, p.(Arg56*) together with a novel heterozygous variant c.205C>T, p.(Arg69Cys) and a second patient with a novel homozygous c.325C>T, p.(Arg109Trp) variant. The two patients presented with different phenotypes; the first patient presented as an adult with aminoaciduria, seizures, bilateral sensorineural deafness and learning difficulties. The second patient was an infant who presented with a classical GRACILE syndrome leading to death at 4 months of age. A decrease in BCS1L protein levels was seen in both patients, and biochemical analysis of Complex III revealed normal respiratory chain enzyme activities in the muscle of both patients. A decrease in Complex III assembly was detected in the adult patient's muscle, whilst the paediatric patient displayed a combined mitochondrial respiratory chain defect in cultured fibroblasts. Yeast complementation studies indicate that the two missense variants, c.205C>T, p.(Arg69Cys) and c.325C>T, p.(Arg109Trp), impair the respiratory capacity of the cell. Together, these data support the pathogenicity of the novel BCS1L variants identified in our patients.
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http://dx.doi.org/10.1093/hmg/ddz202DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6935384PMC
November 2019

Trading amino acids at the aphid- symbiotic interface.

Proc Natl Acad Sci U S A 2019 08 23;116(32):16003-16011. Epub 2019 Jul 23.

Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, NE2 4HH, Newcastle upon Tyne, United Kingdom;

Plant sap-feeding insects are widespread, having evolved to occupy diverse environmental niches despite exclusive feeding on an impoverished diet lacking in essential amino acids and vitamins. Success depends exquisitely on their symbiotic relationships with microbial symbionts housed within specialized eukaryotic bacteriocyte cells. Each bacteriocyte is packed with symbionts that are individually surrounded by a host-derived symbiosomal membrane representing the absolute host-symbiont interface. The symbiosomal membrane must be a dynamic and selectively permeable structure to enable bidirectional and differential movement of essential nutrients, metabolites, and biosynthetic intermediates, vital for growth and survival of host and symbiont. However, despite this crucial role, the molecular basis of membrane transport across the symbiosomal membrane remains unresolved in all bacteriocyte-containing insects. A transport protein was immunolocalized to the symbiosomal membrane separating the pea aphid from its intracellular symbiont The transporter, nonessential amino acid transporter 1, or ApNEAAT1 (gene: ), was characterized functionally following heterologous expression in oocytes, and mediates both inward and outward transport of small dipolar amino acids (serine, proline, cysteine, alanine, glycine). Electroneutral ApNEAAT1 transport is driven by amino acid concentration gradients and is not coupled to transmembrane ion gradients. Previous metabolite profiling of hemolymph and bacteriocyte, alongside metabolic pathway analysis in host and symbiont, enable prediction of a physiological role for ApNEAAT1 in bidirectional host-symbiont amino acid transfer, supplying both host and symbiont with indispensable nutrients and biosynthetic precursors to facilitate metabolic complementarity.
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http://dx.doi.org/10.1073/pnas.1906223116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6690024PMC
August 2019

Identification of a novel orally bioavailable ERK5 inhibitor with selectivity over p38α and BRD4.

Eur J Med Chem 2019 Sep 25;178:530-543. Epub 2019 May 25.

Newcastle Drug Discovery, Northern Institute for Cancer Research, School of Chemistry, Bedson Building, Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK. Electronic address:

Extracellular regulated kinase 5 (ERK5) signalling has been implicated in driving a number of cellular phenotypes including endothelial cell angiogenesis and tumour cell motility. Novel ERK5 inhibitors were identified using high throughput screening, with a series of pyrrole-2-carboxamides substituted at the 4-position with an aroyl group being found to exhibit IC values in the micromolar range, but having no selectivity against p38α MAP kinase. Truncation of the N-substituent marginally enhanced potency (∼3-fold) against ERK5, but importantly attenuated inhibition of p38α. Systematic variation of the substituents on the aroyl group led to the selective inhibitor 4-(2-bromo-6-fluorobenzoyl)-N-(pyridin-3-yl)-1H-pyrrole-2-carboxamide (IC 0.82 μM for ERK5; IC > 120 μM for p38α). The crystal structure (PDB 5O7I) of this compound in complex with ERK5 has been solved. This compound was orally bioavailable and inhibited bFGF-driven Matrigel plug angiogenesis and tumour xenograft growth. The selective ERK5 inhibitor described herein provides a lead for further development into a tool compound for more extensive studies seeking to examine the role of ERK5 signalling in cancer and other diseases.
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http://dx.doi.org/10.1016/j.ejmech.2019.05.057DOI Listing
September 2019

Bialleleic PKD1 mutations underlie early-onset autosomal dominant polycystic kidney disease in Saudi Arabian families.

Pediatr Nephrol 2019 09 11;34(9):1615-1623. Epub 2019 May 11.

Department of Genetics, King Faisal Specialist Hospital and Research Centre, P. O. Box 3354, Riyadh, 11211, Saudi Arabia.

Background: Polycystic kidney disease (PKD) is one of the most common genetic renal diseases and may be inherited in an autosomal dominant or autosomal recessive pattern. Pathogenic variants in two major genes, PKD1 and PKD2, and two rarer genes, GANAB and DNAJB11, cause autosomal dominant PKD (ADPKD). Early onset and severe PKD can occur with PKD1 and PKD2 pathogenic variants and such phenotypes may be modified by second alleles inherited in trans. Homozygous or compound heterozygous hypomorphic PKD1 variants may also cause a moderate to severe disease PKD phenotype.

Methods: Targeted renal gene panel followed by Sanger sequencing of PKD1 gene were employed to investigate molecular causes in early onset PKD patients.

Results: In this study, we report four consanguineous Saudi Arabian families with early onset PKD which were associated with biallelic variants in PKD1 gene.

Conclusions: Our findings confirm that PKD1 alleles may combine to produce severe paediatric onset PKD mimicking the more severe autosomal recessive ciliopathy syndromes associated with PKD. Screening of parents of such children may also reveal subclinical PKD phenotypes.
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http://dx.doi.org/10.1007/s00467-019-04267-xDOI Listing
September 2019

ARL3 Mutations Cause Joubert Syndrome by Disrupting Ciliary Protein Composition.

Am J Hum Genet 2018 10 27;103(4):612-620. Epub 2018 Sep 27.

Institute of Genetic Medicine, Newcastle University, International Centre for Life, Central Parkway, Newcastle upon Tyne NE1 3BZ, UK; Renal Services, Newcastle Hospitals NHS Foundation Trust, Newcastle upon Tyne NE7 7DN, UK. Electronic address:

Joubert syndrome (JBTS) is a genetically heterogeneous autosomal-recessive neurodevelopmental ciliopathy. We investigated further the underlying genetic etiology of Joubert syndrome by studying two unrelated families in whom JBTS was not associated with pathogenic variants in known JBTS-associated genes. Combined autozygosity mapping of both families highlighted a candidate locus on chromosome 10 (chr10: 101569997-109106128, UCSC Genome Browser hg 19), and exome sequencing revealed two missense variants in ARL3 within the candidate locus. The encoded protein, ADP ribosylation factor-like GTPase 3 (ARL3), is a small GTP-binding protein that is involved in directing lipid-modified proteins into the cilium in a GTP-dependent manner. Both missense variants replace the highly conserved Arg149 residue, which we show to be necessary for the interaction with its guanine nucleotide exchange factor ARL13B, such that the mutant protein is associated with reduced INPP5E and NPHP3 localization in cilia. We propose that ARL3 provides a potential hub in the network of proteins implicated in ciliopathies, whereby perturbation of ARL3 leads to the mislocalization of multiple ciliary proteins as a result of abnormal displacement of lipidated protein cargo.
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http://dx.doi.org/10.1016/j.ajhg.2018.08.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6174286PMC
October 2018

Clinical, biochemical, and pathophysiological analysis of SLC34A1 mutations.

Physiol Rep 2018 06;6(12):e13715

Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle, United Kingdom.

Mutations in SLC34A1, encoding the proximal tubular sodium-phosphate transporter NaPi-IIa, may cause a range of clinical phenotypes including infantile hypercalcemia, a proximal renal Fanconi syndrome, which are typically autosomal recessive, and hypophosphatemic nephrolithiasis, which may be an autosomal dominant trait. Here, we report two patients with mixed clinical phenotypes, both with metabolic acidosis, hyperphosphaturia, and renal stones. Patient A had a single heterozygous pathogenic missense mutation (p.I456N) in SLC34A1, consistent with the autosomal dominant pattern of renal stone disease in this family. Patient B, with an autosomal recessive pattern of disease, was compound heterozygous for SLC34A1 variants; a missense variant (p.R512C) together with a relatively common in-frame deletion p.V91A97del7 (91del7). Xenopus oocyte and renal (HKC-8) cell line transfection studies of the variants revealed limited cell surface localization, consistent with trafficking defects. Co-expression of wild-type and I456N and 91del7 appeared to cause intracellular retention in HKC-8, whereas the R512C mutant had a less dominant effect. Expression in Xenopus oocytes failed to demonstrate a significant dominant negative effect for I456N and R512C; however, a negative impact of 91del7 on [ P]phosphate transport was found. In conclusion, we have investigated pathogenic alleles of SLC34A1 which contribute to both autosomal dominant and autosomal recessive renal stone disease.
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http://dx.doi.org/10.14814/phy2.13715DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6010730PMC
June 2018

Acidosis and Deafness in Patients with Recessive Mutations in FOXI1.

J Am Soc Nephrol 2018 03 14;29(3):1041-1048. Epub 2017 Dec 14.

Institute of Genetic Medicine, Newcastle University, Newcastle Upon Tyne, United Kingdom.

Maintenance of the composition of inner ear fluid and regulation of electrolytes and acid-base homeostasis in the collecting duct system of the kidney require an overlapping set of membrane transport proteins regulated by the forkhead transcription factor FOXI1. In two unrelated consanguineous families, we identified three patients with novel homozygous missense mutations in (p.L146F and p.R213P) predicted to affect the highly conserved DNA binding domain. Patients presented with early-onset sensorineural deafness and distal renal tubular acidosis. In cultured cells, the mutations reduced the DNA binding affinity of FOXI1, which hence, failed to adequately activate genes crucial for normal inner ear function and acid-base regulation in the kidney. A substantial proportion of patients with a clinical diagnosis of inherited distal renal tubular acidosis has no identified causative mutations in currently known disease genes. Our data suggest that recessive mutations in FOXI1 can explain the disease in a subset of these patients.
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http://dx.doi.org/10.1681/ASN.2017080840DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5827603PMC
March 2018

Resculpting the binding pocket of APC superfamily LeuT-fold amino acid transporters.

Cell Mol Life Sci 2018 03 23;75(5):921-938. Epub 2017 Oct 23.

Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.

Amino acid transporters are essential components of prokaryote and eukaryote cells, possess distinct physiological functions, and differ markedly in substrate specificity. Amino acid transporters can be both drug targets and drug transporters (bioavailability, targeting) with many monogenic disorders resulting from dysfunctional membrane transport. The largest collection of amino acid transporters (including the mammalian SLC6, SLC7, SLC32, SLC36, and SLC38 families), across all kingdoms of life, is within the Amino acid-Polyamine-organoCation (APC) superfamily. The LeuT-fold is a paradigm structure for APC superfamily amino acid transporters and carriers of sugars, neurotransmitters, electrolytes, osmolytes, vitamins, micronutrients, signalling molecules, and organic and fatty acids. Each transporter is specific for a unique sub-set of solutes, specificity being determined by how well a substrate fits into each binding pocket. However, the molecular basis of substrate selectivity remains, by and large, elusive. Using an integrated computational and experimental approach, we demonstrate that a single position within the LeuT-fold can play a crucial role in determining substrate specificity in mammalian and arthropod amino acid transporters within the APC superfamily. Systematic mutation of the amino acid residue occupying the equivalent position to LeuT V104 titrates binding pocket space resulting in dramatic changes in substrate selectivity in exemplar APC amino acid transporters including PAT2 (SLC36A2) and SNAT5 (SLC38A5). Our work demonstrates how a single residue/site within an archetypal structural motif can alter substrate affinity and selectivity within this important superfamily of diverse membrane transporters.
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http://dx.doi.org/10.1007/s00018-017-2677-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5809530PMC
March 2018

A novel homozygous UMOD mutation reveals gene dosage effects on uromodulin processing and urinary excretion.

Nephrol Dial Transplant 2017 Dec;32(12):1994-1999

Renal Unit, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, UK.

Heterozygous mutations in UMOD encoding the urinary protein uromodulin are the most common genetic cause of autosomal dominant tubulointerstitial kidney disease (ADTKD). We describe the exceptional case of a patient from a consanguineous family carrying a novel homozygous UMOD mutation (p.C120Y) affecting a conserved cysteine residue within the EGF-like domain III of uromodulin. Comparison of heterozygote and homozygote mutation carriers revealed a gene dosage effect with unprecedented low levels of uromodulin and aberrant uromodulin fragments in the urine of the homozygote proband. Despite an amplified biological effect of the homozygote mutation, the proband did not show a strikingly more severe clinical evolution nor was the near absence of urinary uromodulin associated with urinary tract infections or kidney stones.
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http://dx.doi.org/10.1093/ndt/gfx066DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5837645PMC
December 2017

Genetic spectrum of Saudi Arabian patients with antenatal cystic kidney disease and ciliopathy phenotypes using a targeted renal gene panel.

J Med Genet 2016 05 9;53(5):338-47. Epub 2016 Feb 9.

Genetics Department, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia Medicine Department, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia.

Background: Inherited cystic kidney disorders are a common cause of end-stage renal disease. Over 50 ciliopathy genes, which encode proteins that influence the structure and function of the primary cilia, are implicated in cystic kidney disease.

Methods: To define the phenotype and genotype of cystic kidney disease in fetuses and neonates, we correlated antenatal ultrasound examination and postnatal renal ultrasound examination with targeted exon sequencing, using a renal gene panel. A cohort of 44 families in whom antenatal renal ultrasound scanning findings in affected cases included bilateral cystic kidney disease, echogenic kidneys or enlarged kidneys was investigated.

Results: In this cohort, disease phenotypes were severe with 36 cases of stillbirth or perinatal death. Extra renal malformations, including encephalocele, polydactyly and heart malformations, consistent with ciliopathy phenotypes, were frequently detected. Renal gene panel testing identified causative mutations in 21 out of 34 families (62%), where patient and parental DNA was available. In the remaining 10 families, where only parental DNA was available, 7 inferred causative mutations were found. Together, mutations were found in 12 different genes with a total of 13 novel pathogenic variants, including an inferred novel variant in NEK8. Mutations in CC2D2A were the most common cause of an antenatal cystic kidney disease and a suspected ciliopathy in our cohort.

Conclusions: In families with ciliopathy phenotypes, mutational analysis using a targeted renal gene panel allows a rapid molecular diagnosis and provides important information for patients, parents and their physicians.
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http://dx.doi.org/10.1136/jmedgenet-2015-103469DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4853542PMC
May 2016

Clinical and genetic analysis of patients with cystinuria in the United Kingdom.

Clin J Am Soc Nephrol 2015 Jul 11;10(7):1235-45. Epub 2015 May 11.

Academic and Children's Renal Unit, School of Clinical Sciences, University of Bristol, Bristol, United Kingdom;

Background And Objectives: Cystinuria is a rare inherited renal stone disease. Mutations in the amino acid exchanger System b(0,+), the two subunits of which are encoded by SLC3A1 and SLC7A9, predominantly underlie this disease. The work analyzed the epidemiology of cystinuria and the influence of mutations in these two genes on disease severity in a United Kingdom cohort.

Design, Setting, Participants, & Measurements: Prevalent patients were studied from 2012 to 2014 in the northeast and southwest of the United Kingdom. Clinical phenotypes were defined, and genetic analysis of SLC3A1 and SLC7A9 combining Sanger sequencing and multiplex ligation probe-dependent amplification was performed.

Results: In total, 76 patients (42 men and 34 women) were studied. All subjects had proven cystine stones. Median age of presentation (first stone episode) was 24 years old, but 21% of patients presented after 40 years old. Patients had varied clinical courses, with 37% of patients having ≥10 stone episodes; 70% had evidence of CKD, and 9% had reached ESRD as a result of cystinuria and its complications. Patients with cystinuria received a variety of different therapies, with no obvious treatment consensus. Notably, 20% of patients had staghorn calculi, with associated impaired renal function in 80% of these patients. Genetic analysis revealed that biallelic mutations were present in either SLC3A1 (n=27) or SLC7A9 (n=20); 22 patients had only one mutated allele detected (SLC3A1 in five patients and SLC7A9 in 17 patients). In total, 37 different mutant variant alleles were identified, including 12 novel mutations; 22% of mutations were caused by large gene rearrangements. No genotype-phenotype association was detected in this cohort.

Conclusions: Patients with cystinuria in the United Kingdom often present atypically with staghorn calculi at ≥40 years old and commonly develop significant renal impairment. There is no association of clinical course with genotype. Treatments directed toward reducing stone burden need to be rationalized and developed to optimize patient care.
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http://dx.doi.org/10.2215/CJN.10981114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4491297PMC
July 2015

A novel LMX1B mutation in a family with end-stage renal disease of 'unknown cause'.

Clin Kidney J 2015 Feb 5;8(1):113-9. Epub 2014 Dec 5.

Institute of Genetic Medicine , International Centre for Life, Newcastle University , Newcastle upon Tyne , UK.

End-stage renal disease (ESRD) presenting in a familial autosomal dominant pattern points to an underlying monogenic cause. Nail-patella syndrome (NPS) is an autosomal dominant disorder that may lead to ESRD caused by mutations in the transcription factor LMX1B. Renal-limited forms of this disease, termed nail-patella-like renal disease (NPLRD), and LMX1B nephropathy have recently been described. We report a large family, from the North East of England, with seven affected members with varying phenotypes of renal disease, ranging from ESRD at 28 years of age to microscopic haematuria and proteinuria and relatively preserved renal function. In this family, there were no extra-renal manifestations to suggest NPS. Genome-wide linkage studies and inheritance by descent (IBD) suggested disease loci on Chromosome 1 and 9. Whole exome sequencing (WES) analysis identified a novel sequence variant (p.R249Q) in the LMX1B gene in each of the three samples submitted, which was confirmed using Sanger sequencing. The variant segregated with the disease in all affected individuals. In silico modelling revealed that R249 is putatively located in close proximity to the DNA phosphoskeleton, supporting a role for this residue in the interaction between the LMX1B homeodomain and its target DNA. WES and analysis of potential target genes, including CD2AP, NPHS2, COL4A3, COL4A4 and COL4A5, did not reveal any co-inherited pathogenic variants. In conclusion, we confirm a novel LMX1B mutation in a large family with an autosomal dominant pattern of nephropathy. This report confirms that LMX1B mutations may cause a glomerulopathy without extra-renal manifestations. A molecular genetic diagnosis of LMX1B nephropathy thus provides a definitive diagnosis, prevents the need for renal biopsies and allows at risk family members to be screened.
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http://dx.doi.org/10.1093/ckj/sfu129DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4310431PMC
February 2015

Identification of compound heterozygous KCNJ1 mutations (encoding ROMK) in a kindred with Bartter's syndrome and a functional analysis of their pathogenicity.

Physiol Rep 2013 Nov 19;1(6):e00160. Epub 2013 Nov 19.

Institute of Genetic Medicine, Newcastle University Central Parkway, Newcastle upon Tyne, NE1 3BZ, U.K. ; Newcastle Hospitals NHS Foundation Trust Newcastle upon Tyne, NE7 7DN, U.K.

A multiplex family was identified with biochemical and clinical features suggestive of Bartter's syndrome (BS). The eldest sibling presented with developmental delay and rickets at 4 years of age with evidence of hypercalciuria and hypokalemia. The second sibling presented at 1 year of age with urinary tract infections, polyuria, and polydipsia. The third child was born after a premature delivery with a history of polyhydramnios and neonatal hypocalcemia. Following corrective treatment she also developed hypercalciuria and a hypokalemic metabolic alkalosis. There was evidence of secondary hyperreninemia and hyperaldosteronism in all three siblings consistent with BS. Known BS genes were screened and functional assays of ROMK (alias KCNJ1, Kir1.1) were carried out in Xenopus oocytes. We detected compound heterozygous missense changes in KCNJ1, encoding the potassium channel ROMK. The S219R/L220F mutation was segregated from father and mother, respectively. In silico modeling of the missense mutations suggested deleterious changes. Studies in Xenopus oocytes revealed that both S219R and L220F had a deleterious effect on ROMK-mediated potassium currents. Coinjection to mimic the compound heterozygosity produced a synergistic decrease in channel function and revealed a loss of PKA-dependent stabilization of PIP2 binding. In conclusion, in a multiplex family with BS, we identified compound heterozygous mutations in KCNJ1. Functional studies of ROMK confirmed the pathogenicity of these mutations and defined the mechanism of channel dysfunction.
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http://dx.doi.org/10.1002/phy2.160DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3871474PMC
November 2013

A molecular genetic analysis of childhood nephrotic syndrome in a cohort of Saudi Arabian families.

J Hum Genet 2013 Jul 18;58(7):480-9. Epub 2013 Apr 18.

Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia.

Nephrotic syndrome (NS) is a renal disease characterized by heavy proteinuria, hypoalbuminemia, edema and hyperlipidemia. Its presentation within the first 3 months of life or in multiple family members suggests an underlying inherited cause. To determine the frequency of inherited NS, 62 cases (representing 49 families with NS) from Saudi Arabia were screened for mutations in NPHS1, NPHS2, LAMB2, PLCE1, CD2AP, MYO1E, WT1, PTPRO and Nei endonuclease VIII-like 1 (NEIL1). We detected likely causative mutations in 25 out of 49 families studied (51%). We found that the most common genetic cause of NS in our cohort was a homozygous mutation in the NPHS2 gene, found in 11 of the 49 families (22%). Mutations in the NPHS1 and PLCE1 genes allowed a molecular genetic diagnosis in 12% and 8% of families, respectively. We detected novel MYO1E mutations in three families (6%). No mutations were found in WT1, PTPRO or NEIL1. The pathogenicity of novel variants was analyzed by in silico tests and by genetic screening of ethnically matched control populations. This is the first report describing the molecular genetics of NS in the Arabian Peninsula.
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http://dx.doi.org/10.1038/jhg.2013.27DOI Listing
July 2013

Amino acid derivatives are substrates or non-transported inhibitors of the amino acid transporter PAT2 (slc36a2).

Biochim Biophys Acta 2011 Jan 4;1808(1):260-70. Epub 2010 Aug 4.

Epithelial Research Group, Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK.

The H(+)-coupled amino acid transporter PAT2 (SLC36A2) transports the amino acids proline, glycine, alanine and hydroxyproline. A physiological role played by PAT2 in amino acid reabsorption in the renal proximal tubule is demonstrated by mutations in SLC36A2 that lead to an iminoglycinuric phenotype (imino acid and glycine uria) in humans. A number of proline, GABA and tryptophan derivatives were examined to determine if they function either as transported substrates or non-transported inhibitors of PAT2. The compounds were investigated following heterologous expression of rat PAT2 in Xenopus laevis oocytes. PAT2 function was characterised by: radiotracer uptake and competition (cis-inhibition) studies; radiotracer efflux and trans-stimulation; and measurement of substrate-induced positive inward current by two-electrode voltage-clamp. In general, the proline derivatives appeared to be transported substrates and the relative ability to induce current flow was closely related to the inhibitory effects on PAT2-mediated l-[(3)H]proline uptake. In contrast, certain heterocyclic GABA derivatives (e.g. l-pipecolic acid) were translocated only slowly. Finally, the tryptophan derivatives inhibited PAT2 function but did not undergo transport. l-Proline uptake was inhibited by 5-hydroxy-l-tryptophan (IC(50) 1.6±0.4mM), α-methyl-d,l-tryptophan (3.5±1.5mM), l-tryptophan, 1-methyl-l-tryptophan and indole-3-propionic acid. Although neither 5-hydroxy-l-tryptophan nor α-methyl-d,l-tryptophan were able to elicit inward current in PAT2-expressing oocytes both reduced the current evoked by l-proline. 5-Hydroxy-l-tryptophan and α-methyl-d,l-tryptophan were unable to trans-stimulate l-proline efflux from PAT2-expressing oocytes, confirming that the two compounds act as non-transported blockers of PAT2. These two tryptophan derivatives should prove valuable experimental tools in future investigations of the physiological roles of PAT2.
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http://dx.doi.org/10.1016/j.bbamem.2010.07.032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3000476PMC
January 2011

Transport of the photodynamic therapy agent 5-aminolevulinic acid by distinct H+-coupled nutrient carriers coexpressed in the small intestine.

J Pharmacol Exp Ther 2010 Jan 29;332(1):220-8. Epub 2009 Sep 29.

Epithelial Research Group, Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Framlington Place, Newcastle University, Newcastle upon Tyne, UK.

5-Aminolevulinic acid (ALA) is a prodrug used in photodynamic therapy, fluorescent diagnosis, and fluorescent-guided resection because it leads to accumulation of the photosensitizer protoporphyrin IX (PpIX) in tumor tissues. ALA has good oral bioavailability, but high oral doses are required to obtain selective PpIX accumulation in colonic tumors because accumulation is also observed in normal gut mucosa. Structural similarities between ALA and GABA led us to test the hypothesis that the H(+)-coupled amino acid transporter PAT1 (SLC36A1) will contribute to luminal ALA uptake. Radiolabel uptake and electrophysiological measurements identified PAT1-mediated H(+)-coupled ALA symport after heterologous expression in Xenopus oocytes. The selectivity of the nontransported inhibitors 5-hydroxytryptophan and 4-aminomethylbenzoic acid for, respectively, PAT1 and the H(+)-coupled di/tripeptide transporter PepT1 (SLC15A1) were examined. 5-Hydroxytryptophan selectively inhibited PAT1-mediated amino acid uptake across the brush-border membrane of the human intestinal (Caco-2) epithelium whereas 4-aminomethylbenzoic acid selectively inhibited PepT1-mediated dipeptide uptake. The inhibitory effects of 5-hydroxytryptophan and 4-aminomethylbenzoic acid were additive, demonstrating that both PAT1 and PepT1 contribute to intestinal transport of ALA. This is the first demonstration of overlap in substrate specificity between these distinct transporters for amino acids and dipeptides. PAT1 and PepT1 expression was monitored by reverse transcriptase-polymerase chain reaction using paired samples of normal and cancer tissue from human colon. mRNA for both transporters was detected. PepT1 mRNA was increased 2.3-fold in cancer tissues. Thus, increased PepT1 expression in colonic cancer could contribute to the increased PpIX accumulation observed. Selective inhibition of PAT1 could enhance PpIX loading in tumor tissue relative to that in normal tissue.
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http://dx.doi.org/10.1124/jpet.109.159822DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2802479PMC
January 2010