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Kalay I, Aykut H, Caliskan Z, Yigit G, Wollnik B. Lysinuric protein intolerance caused by a homozygous SLC7A7 deletion and presented with hyperferritinemia and osteoporosis in two siblings. Mol Genet Metab Rep 2023; 37:101022. [PMID: 38053936 PMCID: PMC10694772 DOI: 10.1016/j.ymgmr.2023.101022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 11/08/2023] [Accepted: 11/08/2023] [Indexed: 12/07/2023] Open
Abstract
Lysinuric protein intolerance (LPI) is a rare, inherited aminoaciduria caused by biallelic pathogenic variants in the amino acid transporter gene SLC7A7 (OMIM *603593). Individuals with LPI show extreme variability in their clinical presentation, and LPI is included in the differential diagnosis of several disorders such as urea cycle disorders, lysosomal storage diseases, malabsorption diseases, autoimmune disorders, hemochromatosis, and osteoporosis. The phenotypic variability of LPI and the lack of a specific clinical presentation have caused various misdiagnoses. Here, we report two siblings diagnosed in their 4th decade of life with LPI, manifesting rare hyperferritinemia. Additionally, they presented with short stature, multiple bone fractures due to osteoporosis, and they showed an aversion to protein-rich food. Using a combination of exome sequencing, microarray analysis and qPCR, we identified a novel homozygous deletion in SLC7A7 encompassing exons 3 to 10, which is predicted to lead to disruption of SLC7A7 function. This is the first report of lysinuric protein intolerance in a Turkish family associated with this so far unknown deletion in SLC7A7.
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Affiliation(s)
- Irem Kalay
- Institute of Human Genetics, University Medical Center Göttingen, Göttingen, Germany
- Department of Medical Genetics, Umraniye Training and Research Hospital, University of Health Sciences Turkey, Istanbul, Turkey
| | - Hüseyin Aykut
- Department of Gastroenterology, Umraniye Training and Research Hospital, University of Health Sciences Turkey, Istanbul, Turkey
| | - Zuhal Caliskan
- Department of Gastroenterology, Umraniye Training and Research Hospital, University of Health Sciences Turkey, Istanbul, Turkey
| | - Gökhan Yigit
- Institute of Human Genetics, University Medical Center Göttingen, Göttingen, Germany
- DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany
| | - Bernd Wollnik
- Institute of Human Genetics, University Medical Center Göttingen, Göttingen, Germany
- DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
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Lokuhewage C, Pathiraja H, Madawala P, Bandara S, Mettananda S. Lysinuric protein intolerance presenting as pancytopenia and splenomegaly mimicking acute leukaemia: a case report. BMC Pediatr 2023; 23:382. [PMID: 37528333 PMCID: PMC10391768 DOI: 10.1186/s12887-023-04207-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Accepted: 07/21/2023] [Indexed: 08/03/2023] Open
Abstract
BACKGROUND Lysinuric protein intolerance is a rare inherited metabolic disease due to autosomal recessive mutations of the SLC7A7 gene. The affected patients commonly present with protein-rich food intolerance, failure to thrive, hepatosplenomegaly, muscle hypotonia and lung involvement due to impaired intestinal absorption and excessive urinary excretion of dibasic amino acids. Presentation with splenomegaly and cytopenia without other features has not been reported. Here we report a Sri Lankan girl with lysinuric protein intolerance presenting with pancytopenia and splenomegaly mimicking acute leukaemia. CASE PRESENTATION Two years and six months old Sri Lankan girl presented with persistent pancytopenia following a viral illness. She was asymptomatic without vomiting, diarrhoea, abdominal pain or irritability. Physical examination revealed pallor and isolated firm splenomegaly of 2 cm. Growth parameters and other system examinations were normal. Full blood count revealed anaemia, leukopenia and thrombocytopenia. The blood picture showed a mixture of hypochromic microcytic and normochromic normocytic red cells with occasional pencil cells and macrocytes. Bone marrow examination was normal except for occasional megaloblasts; however, serum vitamin B12 and red blood cell folate were normal. The metabolic screen showed a high anion gap compensated metabolic acidosis, high lactate and ketosis. Genetic mutation analysis using whole exome sequencing revealed compound heterozygous variants of the SLC7A7 gene, confirming the diagnosis of lysinuric protein intolerance. CONCLUSION We report a child with lysinuric protein intolerance presenting with pancytopenia and splenomegaly without other disease features. This case report adds to the heterogenic presentations of lysinuric protein intolerance, which is considered a multifaceted disease.
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Affiliation(s)
| | | | | | | | - Sachith Mettananda
- Colombo North Teaching Hospital, Ragama, Sri Lanka.
- Department of Paediatrics, Faculty of Medicine, University of Kelaniya, Thalagolla Road, Ragama, 11010, Sri Lanka.
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Hashmi SB, Ahmed S. Children with lysinuric protein intolerance: Experience from a lower middle income country. World J Clin Pediatr 2022; 11:369-374. [PMID: 36052112 PMCID: PMC9331405 DOI: 10.5409/wjcp.v11.i4.369] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 03/21/2022] [Accepted: 06/03/2022] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Lysinuric protein intolerance (LPI) is an inborn error of metabolism consequential to recessive mutations in the SLC7A7 gene. The metabolic imbalance in absorption and excretion of dibasic amino acids is considered the basis of LPI. The disease results from protein intolerance with signs and symptoms oscillating from cerebral impairment, respiratory involvement, renal failure and autoimmune complications.
AIM To determine biochemical and clinical presentation of cases with biochemical picture suggestive of LPI in Pakistani children.
METHODS The study was conducted at the Biochemical Genetic Lab, Department of Pathology and Laboratory Medicine, AKU Plasma, and urine amino acid quantification data from January 2013 to October 2018 was included in this study. The amino acids were analyzed by high performance liquid chromatography. Prestructured requisition forms were used to obtain the clinicopathological data. Statistical analysis was done by Microsoft Excel 2017.
RESULTS A total of 6 patients were recognized. All the patients were male (100%). The mean age was 24 mo ± 10 d. All the patients had low plasma concentration of lysine, ornithine and arginine, whereas increased levels of lysine, ornithine and arginine in urine were observed in 2 patients. History of consanguineous marriage was present in all patients (100%). The most observed clinical symptom was feeding difficulty followed by failure to thrive (83.3%) and developmental delay (66.6%). Hepatomegaly was present in all patients (100%). No mutation analysis was done.
CONCLUSION This study portrays the biochemical and clinical spectrum of LPI in Pakistan. Although clinical manifestations appeared in the first 2 years of life, most of them suffered a delay in undergoing diagnostic workup.
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Affiliation(s)
- Syed Bilal Hashmi
- Department of Pathology and Laboratory Medicine, Aga Khan University Hospital, Karachi 74800, Pakistan
| | - Sibtain Ahmed
- Department of Pathology and Laboratory Medicine, Aga Khan University Hospital, Karachi 74800, Pakistan
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Matsukawa Y, Sakamoto K, Ikeda Y, Taga T, Kosaki K, Maruo Y. Familial hemophagocytic lymphohistiocytosis syndrome due to lysinuric protein intolerance: a patient with a novel compound heterozygous pathogenic variant in SLC7A7. Int J Hematol 2022; 116:635-638. [DOI: 10.1007/s12185-022-03375-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Revised: 04/21/2022] [Accepted: 04/21/2022] [Indexed: 10/18/2022]
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Contreras JL, Ladino MA, Aránguiz K, Mendez GP, Coban-Akdemir Z, Yuan B, Gibbs RA, Burrage LC, Lupski JR, Chinn IK, Vogel TP, Orange JS, Poli MC. Immune Dysregulation Mimicking Systemic Lupus Erythematosus in a Patient With Lysinuric Protein Intolerance: Case Report and Review of the Literature. Front Pediatr 2021; 9:673957. [PMID: 34095032 PMCID: PMC8172984 DOI: 10.3389/fped.2021.673957] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Accepted: 04/14/2021] [Indexed: 12/14/2022] Open
Abstract
Lysinuric protein intolerance (LPI) is an inborn error of metabolism caused by defective transport of cationic amino acids in epithelial cells of intestines, kidneys and other tissues as well as non-epithelial cells including macrophages. LPI is caused by biallelic, pathogenic variants in SLC7A7. The clinical phenotype of LPI includes failure to thrive and multi-system disease including hematologic, neurologic, pulmonary and renal manifestations. Individual presentations are extremely variable, often leading to misdiagnosis or delayed diagnosis. Here we describe a patient that clinically presented with immune dysregulation in the setting of early-onset systemic lupus erythematosus (SLE), including renal involvement, in whom an LPI diagnosis was suspected post-mortem based on exome sequencing analysis. A review of the literature was performed to provide an overview of the clinical spectrum and immune mechanisms involved in this disease. The precise mechanism by which ineffective amino acid transport triggers systemic inflammatory features is not yet understood. However, LPI should be considered in the differential diagnosis of early-onset SLE, particularly in the absence of response to immunosuppressive therapy.
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Affiliation(s)
| | - Mabel A. Ladino
- Universidad de Chile, Reumatóloga Pediátrica Hospital San Juan de Dios, Santiago, Chile
| | - Katherine Aránguiz
- Unidad de Inmunología y Reumatología Hospital Luis Calvo Mackenna, Providencia, Chile
| | - Gonzalo P. Mendez
- Patológo Renal, Departamento de Anatomía Patológica, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Zeynep Coban-Akdemir
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Human Genetics Center, Department of Epidemiology, Human Genetics, and Environmental Sciences, School of Public Health, The University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Bo Yuan
- Department of Laboratories, Seattle Children's Hospital, Seattle, WA, United States
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, United States
| | - Richard A. Gibbs
- Sequencing Center, Baylor College of Medicine, Houston, TX, United States
| | - Lindsay C. Burrage
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Texas Children's Hospital, Houston, TX, United States
| | - James R. Lupski
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Sequencing Center, Baylor College of Medicine, Houston, TX, United States
- Texas Children's Hospital, Houston, TX, United States
| | - Ivan K. Chinn
- Texas Children's Hospital, Houston, TX, United States
- Department of Pediatrics, Division of Allergy, Immunology and Retrovirology, Baylor College of Medicine, Houston, TX, United States
| | - Tiphanie P. Vogel
- Texas Children's Hospital, Houston, TX, United States
- Department of Pediatrics, Division of Rheumatology, Baylor College of Medicine, Houston, TX, United States
| | - Jordan S. Orange
- Department of Pediatrics, Vagelos College of Physicians and Surgeons, New York Presbyterian Morgan Stanley Children's Hospital, Columbia University, New York, NY, United States
| | - M. Cecilia Poli
- Facultad de Medicina Universidad del Desarrollo-Clínica Alemana, Santiago, Chile
- Department of Pediatrics, Division of Allergy, Immunology and Retrovirology, Baylor College of Medicine, Houston, TX, United States
- Unidad de Inmunología y Reumatología, Hospital Roberto del Río, Santiago, Chile
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Al-Qattan S, Malcolmson C, Mercimek-Andrews S. Lysinuric protein intolerance mimicking N-acetylglutamate synthase deficiency in a nine-year-old boy. Mol Genet Metab Rep 2021; 27:100741. [PMID: 33763330 PMCID: PMC7973239 DOI: 10.1016/j.ymgmr.2021.100741] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Revised: 02/28/2021] [Accepted: 03/01/2021] [Indexed: 12/01/2022] Open
Abstract
We report a 9-year-old boy with lysinuric protein intolerance (LPI). He had developmental delay, short stature, failure to thrive, high-protein food aversion, hypothyroidism, growth hormone deficiency, features of hemophagocytic lymphohistiocytosis (HLH), decreased bone mineral density and multiple thoracic spine compression fractures on X-ray. LPI was suspected, but urine amino acid profile and normal orotic acid did not suggest biochemical diagnosis of LPI. Targeted next generation sequencing panel for HLH (including SLC7A7) was organized. Due to elevated glutamine in plasma amino acid analysis, a metabolic consultation was initiated and his asymptomatic post-prandial ammonia was 295 μmol/L. We then suspected n-acetylglutamate synthase or carbamoyl-phosphate synthase I deficiency due to marked hyperammonemia, elevated glutamine level, normal orotic acid, and normalization of ammonia at 2 h of carglumic acid (200 mg/kg/d). His targeted next generation sequencing panel for HLH revealed homozygous pathogenic variant in SLC7A7 ((NM_001126106.2): c.726G>A (p.Trp242*)) and confirmed the diagnosis of LPI. We emphasize the importance of genetic investigations in the diagnosis of LPI. LPI associated hyperammonemia responds to carbaglumic acid. Protein aversion, and failure to thrive should warrant for ammonia measurement. Multisystem disease should include LPI into the differential diagnosis even in the absence of typical biochemical features.
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Affiliation(s)
- Sarah Al-Qattan
- Division of Clinical and Metabolic Genetics, Department of Pediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Caroline Malcolmson
- Division of Hematology, Department of Pediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Saadet Mercimek-Andrews
- Division of Clinical and Metabolic Genetics, Department of Pediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada
- Department of Medical Genetics, University of Alberta, Stollery Children's Hospital, Edmonton, Alberta, Canada
- Corresponding author at: Department of Medical Genetics, University of Alberta, Stollery Children's Hospital, Alberta Health Services, 8-39 Medical Sciences Building, 8613 – 114 Street, Edmonton, Alberta T6G 2H7, Canada.
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Fairweather SJ, Shah N, Brӧer S. Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 21:13-127. [PMID: 33052588 DOI: 10.1007/5584_2020_584] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H+ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b0,+AT-rBAT and the SLC6 family heteromer B0AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.
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Affiliation(s)
- Stephen J Fairweather
- Research School of Biology, Australian National University, Canberra, ACT, Australia. .,Resarch School of Chemistry, Australian National University, Canberra, ACT, Australia.
| | - Nishank Shah
- Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Stefan Brӧer
- Research School of Biology, Australian National University, Canberra, ACT, Australia.
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Alqarajeh F, Omorodion J, Bosfield K, Shur N, Ferreira CR. Lysinuric protein intolerance: Pearls to detect this otherwise easily missed diagnosis. ACTA ACUST UNITED AC 2020; 5:81-86. [PMID: 33134088 PMCID: PMC7590902 DOI: 10.3233/trd-190035] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
BACKGROUND: Lysinuric protein intolerance (LPI) is a rare autosomal recessive disorder characterized by deficient membrane transport of cationic amino acids. It is caused by pathogenic variants in SLC7A7, resulting in impairment of intestinal import and renal proximal tubule loss of the affected amino acids. LPI typically presents with gastrointestinal symptoms, such as vomiting, diarrhea, and failure to thrive. CASE REPORT: A 4-year-old African-American boy presented with multiple respiratory tract infections, weight loss in the setting of chronic diarrhea and worsening abdominal distention, and multiple episodes of rectal prolapse. Development was unaffected. Laboratory examination demonstrated mild anemia, hypokalemia and hypoalbuminemia, transaminitis, and normal ammonia. Initial urine amino acid analysis did not show major elevations of lysine and ornithine, often lower than expected in the setting of malnutrition. Upon initiation of total parenteral nutrition (TPN), his urine amino acids showed a characteristic profile of dibasic aminoaciduria. CONCLUSIONS: Failure to thrive, chronic diarrhea, and hepatomegaly should raise suspicion for LPI. Urine amino acids can be normal in this condition in the setting of malnutrition, a common complication of the disease. Additionally, it has been previously shown that the plasma arginine and ornithine concentration is higher in LPI subjects.
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Affiliation(s)
- Firas Alqarajeh
- Faculty of Medicine, Al-Quds University, Jerusalem, Palestine
| | - Jacklyn Omorodion
- The George Washington University School of Medicine and Health Sciences, Washington, DC, USA
| | - Kerri Bosfield
- Rare Disease Institute, Children's National Health System, Washington, DC, USA
| | - Natasha Shur
- Rare Disease Institute, Children's National Health System, Washington, DC, USA
| | - Carlos R Ferreira
- National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA
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Noguchi A, Takahashi T. Overview of symptoms and treatment for lysinuric protein intolerance. J Hum Genet 2019; 64:849-858. [PMID: 31213652 DOI: 10.1038/s10038-019-0620-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2018] [Revised: 05/16/2019] [Accepted: 05/16/2019] [Indexed: 12/30/2022]
Abstract
Lysinuric protein intolerance (LPI) is caused by dysfunction of the dibasic amino acid membrane transport owing to the functional abnormality of y+L amino acid transporter-1 (y+ LAT-1). LPI is associated with autosomal recessive inheritance and pathological variants in the responsible gene SLC7A7 are also observed. The pathophysiology of this disease had earlier been understood as a transport defect in polarized cells (e.g., intestinal or renal tubular epithelium); however, in recent years, transport defects in non-polarized cells such as lymphocytes and macrophages have also been recognized as important. Although the former can cause death, malnutrition, and urea cycle dysfunction (hyperammonemia), the latter can induce renal, pulmonary, and immune disorders. Furthermore, although therapeutic interventions can prevent hyperammonemic episodes to some extent, progression of pulmonary and renal complications cannot be prevented, thereby influencing prognosis. Such pathological conditions are currently being explored and further investigation would prove beneficial. In this study, we have summarized the basic pathology as revealed in recent years, along with the clinical aspects and genetic features.
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Affiliation(s)
- Atsuko Noguchi
- Akita University Graduate School of Medicine, Pediatrics, Akita, Akita, Japan.
| | - Tsutomu Takahashi
- Akita University Graduate School of Medicine, Pediatrics, Akita, Akita, Japan
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Abstract
The small intestine mediates the absorption of amino acids after ingestion of protein and sustains the supply of amino acids to all tissues. The small intestine is an important contributor to plasma amino acid homeostasis, while amino acid transport in the large intestine is more relevant for bacterial metabolites and fluid secretion. A number of rare inherited disorders have contributed to the identification of amino acid transporters in epithelial cells of the small intestine, in particular cystinuria, lysinuric protein intolerance, Hartnup disorder, iminoglycinuria, and dicarboxylic aminoaciduria. These are most readily detected by analysis of urine amino acids, but typically also affect intestinal transport. The genes underlying these disorders have all been identified. The remaining transporters were identified through molecular cloning techniques to the extent that a comprehensive portrait of functional cooperation among transporters of intestinal epithelial cells is now available for both the basolateral and apical membranes. Mouse models of most intestinal transporters illustrate their contribution to amino acid homeostasis and systemic physiology. Intestinal amino acid transport activities can vary between species, but these can now be explained as differences of amino acid transporter distribution along the intestine. © 2019 American Physiological Society. Compr Physiol 9:343-373, 2019.
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Affiliation(s)
- Stefan Bröer
- Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia
| | - Stephen J Fairweather
- Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia
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Variable X-chromosome inactivation and enlargement of pericentral glutamine synthetase zones in the liver of heterozygous females with OTC deficiency. Virchows Arch 2018; 472:1029-1039. [PMID: 29623395 DOI: 10.1007/s00428-018-2345-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2017] [Revised: 02/27/2018] [Accepted: 03/23/2018] [Indexed: 01/28/2023]
Abstract
Ornithine transcarbamylase (OTC) deficiency is an X-linked disorder that causes recurrent and life-threatening episodes of hyperammonemia. The clinical picture in heterozygous females is highly diverse and derives from the genotype and the degree of inactivation of the mutated X chromosome in hepatocytes. Here, we describe molecular genetic, biochemical, and histopathological findings in the livers explanted from two female patients with late-onset OTC deficiency. Analysis of X-inactivation ratios by DNA methylation-based assays showed remarkable intra-organ variation ranging from 46:54 to 82:18 (average 70:30, n = 37), in favor of the active X chromosome carrying the mutation c.583G>C (p.G195R), in the first patient and from 75:25 to 90:10 (average 82:18, n = 20) in favor of the active X chromosome carrying the splicing mutation c.663+1G>A in the second patient. The X-inactivation ratios in liver samples correlated highly with the proportions of OTC-positive hepatocytes calculated from high-resolution image analyses of the immunohistochemically detected OTC in frozen sections that was performed on total area > 5 cm2. X-inactivation ratios in blood in both female patients corresponded to the lower limit of the liver values. Our data indicate that the proportion of about 20-30% of hepatocytes expressing the functional OTC protein is not sufficient to maintain metabolic stability. X-inactivation ratios assessed in liver biopsies taken from heterozygous females with X-linked disorders should not be considered representative of the whole liver.
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