1
|
Fraga G, Herreros MA, Pybus M, Aza-Carmona M, Pilco-Teran M, Furlano M, García-Borau MJ, Torra R, Ars E. A Mild Presentation of X-Linked Hypophosphatemia Caused by a Non-Canonical Splice Site Variant in the PHEX Gene. Genes (Basel) 2024; 15:679. [PMID: 38927615 PMCID: PMC11202505 DOI: 10.3390/genes15060679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 05/17/2024] [Accepted: 05/21/2024] [Indexed: 06/28/2024] Open
Abstract
X-linked hypophosphatemia (XLH) is a rare inherited disorder of renal phosphate wasting with a highly variable phenotype caused by loss-of-function variants in the PHEX gene. The diagnosis of individuals with mild phenotypes can be challenging and often delayed. Here, we describe a three-generation family with a very mild clinical presentation of XLH. The diagnosis was unexpectedly found in a 39-year-old woman who was referred for genetic testing due to an unclear childhood diagnosis of a tubulopathy. Genetic testing performed by next-generation sequencing using a kidney disease gene panel identified a novel non-canonical splice site variant in the PHEX gene. Segregation analysis detected that the consultand's father, who presented with hypophosphatemia and decreased tubular phosphate reabsorption, and the consultand's son also carried this variant. RNA studies demonstrated that the non-canonical splice site variant partially altered the splicing of the PHEX gene, as both wild-type and aberrant splicing transcripts were detected in the two male members with only one copy of the PHEX gene. In conclusion, this case contributes to the understanding of the relationship between splicing variants and the variable expressivity of XLH disease. The mild phenotype of this family can be explained by the coexistence of PHEX transcripts with aberrant and wild-type splicing.
Collapse
Affiliation(s)
- Gloria Fraga
- Pediatric Nephrology Department, Hospital de la Santa Creu i Sant Pau, Institut de Recerca Sant Pau (IR Sant Pau), RICORS-SAMID, Universitat Autònoma de Barcelona, 08193 Barcelona, Catalonia, Spain;
| | - M. Alba Herreros
- Nephrology Department, Fundació Puigvert, Institut de Recerca Sant Pau (IR-Sant Pau), RICORS2040 (Kidney Disease), Department of Medicine, Universitat Autònoma de Barcelona, 08193 Barcelona, Catalonia, Spain
| | - Marc Pybus
- Molecular Biology Laboratory, Fundació Puigvert, Institut de Recerca Sant Pau (IR-Sant Pau), RICORS2040 (Kidney Disease), 08193 Barcelona, Catalonia, Spain
| | - Miriam Aza-Carmona
- Molecular Biology Laboratory, Fundació Puigvert, Institut de Recerca Sant Pau (IR-Sant Pau), RICORS2040 (Kidney Disease), 08193 Barcelona, Catalonia, Spain
| | - Melissa Pilco-Teran
- Nephrology Department, Fundació Puigvert, Institut de Recerca Sant Pau (IR-Sant Pau), RICORS2040 (Kidney Disease), Department of Medicine, Universitat Autònoma de Barcelona, 08193 Barcelona, Catalonia, Spain
| | - Mónica Furlano
- Nephrology Department, Fundació Puigvert, Institut de Recerca Sant Pau (IR-Sant Pau), RICORS2040 (Kidney Disease), Department of Medicine, Universitat Autònoma de Barcelona, 08193 Barcelona, Catalonia, Spain
| | - M. José García-Borau
- Neonatology Unit, Pediatrics Department, Hospital de la Santa Creu i Sant Pau, Universitat Autònoma de Barcelona, 08193 Barcelona, Catalonia, Spain
| | - Roser Torra
- Nephrology Department, Fundació Puigvert, Institut de Recerca Sant Pau (IR-Sant Pau), RICORS2040 (Kidney Disease), Department of Medicine, Universitat Autònoma de Barcelona, 08193 Barcelona, Catalonia, Spain
| | - Elisabet Ars
- Molecular Biology Laboratory, Fundació Puigvert, Institut de Recerca Sant Pau (IR-Sant Pau), RICORS2040 (Kidney Disease), 08193 Barcelona, Catalonia, Spain
| |
Collapse
|
2
|
Heitman K, Alexander MS, Faul C. Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies. Int J Mol Sci 2024; 25:5117. [PMID: 38791164 PMCID: PMC11121428 DOI: 10.3390/ijms25105117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Revised: 05/03/2024] [Accepted: 05/06/2024] [Indexed: 05/26/2024] Open
Abstract
Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.
Collapse
Affiliation(s)
- Kylie Heitman
- Division of Nephrology and Section of Mineral Metabolism, Department of Medicine, Heersink School of Medicine, The University of Alabama at Birmingham, Birmingham, AL 35294, USA;
| | - Matthew S. Alexander
- Division of Neurology, Department of Pediatrics, The University of Alabama at Birmingham and Children’s of Alabama, Birmingham, AL 35294, USA
- Center for Exercise Medicine, The University of Alabama at Birmingham, Birmingham, AL 35294, USA
- Department of Genetics, The University of Alabama at Birmingham, Birmingham, AL 35294, USA
- Civitan International Research Center, The University of Alabama at Birmingham, Birmingham, AL 35294, USA
- Center for Neurodegeneration and Experimental Therapeutics, The University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Christian Faul
- Division of Nephrology and Section of Mineral Metabolism, Department of Medicine, Heersink School of Medicine, The University of Alabama at Birmingham, Birmingham, AL 35294, USA;
| |
Collapse
|
3
|
Sarathi V, Dhananjaya MS, Karlekar M, Lila AR. Vitamin D deficiency or resistance and hypophosphatemia. Best Pract Res Clin Endocrinol Metab 2024; 38:101876. [PMID: 38365463 DOI: 10.1016/j.beem.2024.101876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/18/2024]
Abstract
Vitamin D is mainly produced in the skin (cholecalciferol) by sun exposure while a fraction of it is obtained from dietary sources (ergocalciferol). Vitamin D is further processed to 25-hydroxyvitamin D and 1,25-dihydroxy vitamin D (calcitriol) in the liver and kidneys, respectively. Calcitriol is the active form which mediates the actions of vitamin D via vitamin D receptor (VDR) which is present ubiquitously. Defect at any level in this pathway leads to vitamin D deficient or resistant rickets. Nutritional vitamin D deficiency is the leading cause of rickets and osteomalacia worldwide and responds well to vitamin D supplementation. Inherited disorders of vitamin D metabolism (vitamin D-dependent rickets, VDDR) account for a small proportion of calcipenic rickets/osteomalacia. Defective 1α hydroxylation of vitamin D, 25 hydroxylation of vitamin D, and vitamin D receptor result in VDDR1A, VDDR1B and VDDR2A, respectively whereas defective binding of vitamin D to vitamin D response element due to overexpression of heterogeneous nuclear ribonucleoprotein and accelerated vitamin D metabolism cause VDDR2B and VDDR3, respectively. Impaired dietary calcium absorption and consequent calcium deficiency increases parathyroid hormone in these disorders resulting in phosphaturia and hypophosphatemia. Hypophosphatemia is a common feature of all these disorders, though not a sine-qua-non and leads to hypomineralisation of the bone and myopathy. Improvement in hypophosphatemia is one of the earliest markers of response to vitamin D supplementation in nutritional rickets/osteomalacia and the lack of such a response should prompt evaluation for inherited forms of rickets/osteomalacia.
Collapse
Affiliation(s)
- Vijaya Sarathi
- Department of Endocrinology, Vydehi Institute of Medical Sciences and Research Center, Bengaluru 560066, India.
| | | | - Manjiri Karlekar
- Department of Endocrinology, Seth G S Medical College and King Edward Hospital, Mumbai 400012, India
| | - Anurag Ranjan Lila
- Department of Endocrinology, Seth G S Medical College and King Edward Hospital, Mumbai 400012, India
| |
Collapse
|
4
|
Insogna KL, Sullivan R, Parziale S, Deng Y, Carrano D, Simpson C, Dufour S, Carpenter T, Petersen KF. Effect of Burosumab on Muscle Function and Strength, and Rates of ATP Synthesis in Skeletal Muscle in Adults With XLH. J Clin Endocrinol Metab 2024; 109:e1061-e1071. [PMID: 37930769 DOI: 10.1210/clinem/dgad642] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 10/05/2023] [Accepted: 10/27/2023] [Indexed: 11/07/2023]
Abstract
CONTEXT In clinical trials, burosumab ameliorates symptoms of pain, fatigue, and stiffness and improves performance on certain muscle function studies in patients with X-linked hypophosphatemia (XLH). OBJECTIVE This work aimed to determine if burosumab increases adenosine triphosphate (ATP) synthesis in skeletal muscle of treatment-naive adults with XLH, and if so, whether that correlates with improved muscle function. METHODS Ten untreated, symptomatic adults with XLH had ATP synthesis rates measured in the right calf using the 31P magnetic resonance spectroscopy saturation transfer technique. Baseline muscle function tests and symptoms of pain, fatigue, stiffness, and lower-extremity joint pain were quantified. All participants were treated with burosumab, 1 mg/kg every 4 weeks for 12 weeks. ATP synthesis rates and muscle function tests were repeated 2 weeks ("peak") and 4 weeks ("trough") after the third dose of burosumab. RESULTS All symptoms improved with treatment. Performance on the 6-Minute Walk Test (6MWT) and Sit to Stand (STS) tests also improved. Muscle strength and ATP synthesis rates did not change over the 3 months of the study. When individuals whose performances on the 6MWT and STS test were at or better than the median outcome for those tests were compared to those whose outcomes were below the median, no difference was observed in the rate of change in ATP synthesis. Intracellular muscle concentrations of phosphate were normal. CONCLUSION The improvement in the 6MWT and STS test without changes in muscle strength or ATP synthesis rates suggests that reductions in pain, fatigue, and stiffness may partly explain the improved performance. Intracellular phosphate in skeletal muscle is insulated from hypophosphatemia in XLH.
Collapse
Affiliation(s)
- Karl L Insogna
- Department of Medicine, Section of Endocrinology, Yale School of Medicine, New Haven, CT 06520-8020, USA
| | - Rebecca Sullivan
- Department of Medicine, Section of Endocrinology, Yale School of Medicine, New Haven, CT 06520-8020, USA
| | - Stephen Parziale
- Yale Center for Analytical Sciences, Yale School of Public Health, New Haven, CT 06510, USA
| | - Yanhong Deng
- Yale Center for Analytical Sciences, Yale School of Public Health, New Haven, CT 06510, USA
| | - Diana Carrano
- Rehabilitation Supervisor, Yale New Haven Hospital, New Haven, CT 06510, USA
| | - Christine Simpson
- Department of Medicine, Section of Endocrinology, Yale School of Medicine, New Haven, CT 06520-8020, USA
| | - Sylvie Dufour
- Department of Medicine, Section of Endocrinology, Yale School of Medicine, New Haven, CT 06520-8020, USA
| | - Thomas Carpenter
- Department of Pediatrics, Section of Endocrinology, Yale School of Medicine, New Haven, CT 06510, USA
| | - Kitt Falk Petersen
- Department of Medicine, Section of Endocrinology, Yale School of Medicine, New Haven, CT 06520-8020, USA
| |
Collapse
|
5
|
Sarker S, Eshaque TB, Soorajkumar A, Nassir N, Zehra B, Kanta SI, Rahaman MA, Islam A, Akter S, Ali MK, Mim RA, Uddin KMF, Chowdhury MSJ, Shams N, Baqui MA, Lim ET, Akter H, Woodbury-Smith M, Uddin M. Mutational spectrum and phenotypic variability of Duchenne muscular dystrophy and related disorders in a Bangladeshi population. Sci Rep 2023; 13:21547. [PMID: 38057384 PMCID: PMC10700514 DOI: 10.1038/s41598-023-48982-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 12/02/2023] [Indexed: 12/08/2023] Open
Abstract
Duchenne muscular dystrophy (DMD) is a severe rare neuromuscular disorder caused by mutations in the X-linked dystrophin gene. Several mutations have been identified, yet the full mutational spectrum, and their phenotypic consequences, will require genotyping across different populations. To this end, we undertook the first detailed genotype and phenotype characterization of DMD in the Bangladeshi population. We investigated the rare mutational and phenotypic spectrum of the DMD gene in 36 DMD-suspected Bangladeshi participants using an economically affordable diagnostic strategy involving initial screening for exonic deletions in the DMD gene via multiplex PCR, followed by testing PCR-negative patients for mutations using whole exome sequencing. The deletion mapping identified two critical DMD gene hotspot regions (near proximal and distal ends, spanning exons 8-17 and exons 45-53, respectively) that comprised 95% (21/22) of the deletions for this population cohort. From our exome analysis, we detected two novel pathogenic hemizygous mutations in exons 21 and 42 of the DMD gene, and novel pathogenic recessive and loss of function variants in four additional genes: SGCD, DYSF, COL6A3, and DOK7. Our phenotypic analysis showed that DMD suspected participants presented diverse phenotypes according to the location of the mutation and which gene was impacted. Our study provides ethnicity specific new insights into both clinical and genetic aspects of DMD.
Collapse
Affiliation(s)
- Shaoli Sarker
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
- Bangladesh Shishu Hospital and Institute, Dhaka, Bangladesh
| | | | - Anjana Soorajkumar
- Center for Applied and Translational Genomics (CATG), Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, UAE
| | - Nasna Nassir
- Center for Applied and Translational Genomics (CATG), Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, UAE
| | - Binte Zehra
- Center for Applied and Translational Genomics (CATG), Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, UAE
| | | | - Md Atikur Rahaman
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
| | - Amirul Islam
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
- GenomeArc Inc., Mississauga, Ontario, Canada
| | - Shimu Akter
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
| | - Mohammad Kawsar Ali
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
| | - Rabeya Akter Mim
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
| | - K M Furkan Uddin
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
| | | | - Nusrat Shams
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
| | - Md Abdul Baqui
- Department of Biochemistry, Holy Family Red Crescent Medical College and Hospital, Dhaka, Bangladesh
| | - Elaine T Lim
- Department of Genomics and Computational Biology, University of Massachusetts Chan Medical School, Worcester, MA, 01605, USA
- Department of Molecular, Cell and Cancer Biology, University of Massachusetts Chan Medical School, Worcester, MA, 01605, USA
| | - Hosneara Akter
- Genetics and Genomic Medicine Centre (GGMC), NeuroGen Healthcare, Dhaka, Bangladesh
| | - Marc Woodbury-Smith
- Biosciences Institute, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.
| | - Mohammed Uddin
- Center for Applied and Translational Genomics (CATG), Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, UAE.
- GenomeArc Inc., Mississauga, Ontario, Canada.
| |
Collapse
|
6
|
Jennings ML. Role of transporters in regulating mammalian intracellular inorganic phosphate. Front Pharmacol 2023; 14:1163442. [PMID: 37063296 PMCID: PMC10097972 DOI: 10.3389/fphar.2023.1163442] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Accepted: 03/17/2023] [Indexed: 03/31/2023] Open
Abstract
This review summarizes the current understanding of the role of plasma membrane transporters in regulating intracellular inorganic phosphate ([Pi]In) in mammals. Pi influx is mediated by SLC34 and SLC20 Na+-Pi cotransporters. In non-epithelial cells other than erythrocytes, Pi influx via SLC20 transporters PiT1 and/or PiT2 is balanced by efflux through XPR1 (xenotropic and polytropic retrovirus receptor 1). Two new pathways for mammalian Pi transport regulation have been described recently: 1) in the presence of adequate Pi, cells continuously internalize and degrade PiT1. Pi starvation causes recycling of PiT1 from early endosomes to the plasma membrane and thereby increases the capacity for Pi influx; and 2) binding of inositol pyrophosphate InsP8 to the SPX domain of XPR1 increases Pi efflux. InsP8 is degraded by a phosphatase that is strongly inhibited by Pi. Therefore, an increase in [Pi]In decreases InsP8 degradation, increases InsP8 binding to SPX, and increases Pi efflux, completing a feedback loop for [Pi]In homeostasis. Published data on [Pi]In by magnetic resonance spectroscopy indicate that the steady state [Pi]In of skeletal muscle, heart, and brain is normally in the range of 1–5 mM, but it is not yet known whether PiT1 recycling or XPR1 activation by InsP8 contributes to Pi homeostasis in these organs. Data on [Pi]In in cultured cells are variable and suggest that some cells can regulate [Pi] better than others, following a change in [Pi]Ex. More measurements of [Pi]In, influx, and efflux are needed to determine how closely, and how rapidly, mammalian [Pi]In is regulated during either hyper- or hypophosphatemia.
Collapse
|