scholarly journals Functional Analysis of Monocarboxylate Transporter 8 Mutations Identified in Patients with X-Linked Psychomotor Retardation and Elevated Serum Triiodothyronine

2007 ◽  
Vol 92 (6) ◽  
pp. 2378-2381 ◽  
Author(s):  
Jurgen Jansen ◽  
Edith C. H. Friesema ◽  
Monique H. A. Kester ◽  
Carmelina Milici ◽  
Maarten Reeser ◽  
...  
Keyword(s):  
Elevated Serum ◽  
Splice Site Mutation ◽  
Psychomotor Retardation ◽  
Monocarboxylate Transporter ◽  
Missense Mutations ◽  
Wild Type ◽  
Site Mutation ◽  
Central Neurons ◽  
Serum T3 ◽  
Type 3

Abstract Context: T3 action in neurons is essential for brain development. Recent evidence indicates that monocarboxylate transporter 8 (MCT8) is important for neuronal T3 uptake. Hemizygous mutations have been identified in the X-linked MCT8 gene in boys with severe psychomotor retardation and elevated serum T3 levels. Objective: The objective of this study was to determine the functional consequences of MCT8 mutations regarding transport of T3. Design: MCT8 function was studied in wild-type or mutant MCT8-transfected JEG3 cells by analyzing: 1) T3 uptake, 2) T3 metabolism in cells cotransfected with human type 3 deiodinase, 3) immunoblotting, and 4) immunocytochemistry. Results: The mutations identified in MCT8 comprise four deletions (24.5 kb, 2.4 kb, 14 bp, and 3 bp), three missense mutations (Ala224Val, Arg271His, and Leu471Pro), a nonsense mutation (Arg245stop), and a splice site mutation (94 amino acid deletion). All tested mutants were inactive in uptake and metabolism assays, except MCT8 Arg271His, which showed approximately 20% activity vs. wild-type MCT8. Conclusion: These findings support the hypothesis that the severe psychomotor retardation and elevated serum T3 levels in these patients are caused by inactivation of the MCT8 transporter, preventing action and metabolism of T3 in central neurons.

scholarly journals Pathophysiological Importance of Thyroid Hormone Transporters

Endocrinology ◽  
2009 ◽  
Vol 150 (3) ◽  
pp. 1078-1083 ◽  
Author(s):  
Heike Heuer ◽  
Theo J. Visser
Keyword(s):  
Thyroid Hormone ◽  
Organic Anion ◽  
Elevated Serum ◽  
Psychomotor Retardation ◽  
Monocarboxylate Transporter ◽  
Tissue Specific ◽  
Thyroid Hormone Metabolism ◽  
Serum T3 ◽  
Specific Regulation ◽  
Near Future

Thyroid hormone metabolism and action are largely intracellular events that require transport of iodothyronines across the plasma membrane. It has been assumed for a long time that this occurs by passive diffusion, but it has become increasingly clear that cellular uptake and efflux of thyroid hormone is mediated by transporter proteins. Recently, several active and specific thyroid hormone transporters have been identified, including monocarboxylate transporter 8 (MCT8), MCT10, and organic anion transporting polypeptide 1C1 (OATP1C1). The latter is expressed predominantly in brain capillaries and transports preferentially T4, whereas MCT8 and MCT10 are expressed in multiple tissues and are capable of transporting different iodothyronines. The pathophysiological importance of thyroid hormone transporters has been established by the demonstration of MCT8 mutations in patients with severe psychomotor retardation and elevated serum T3 levels. MCT8 appears to play an important role in the transport of thyroid hormone in the brain, which is essential for the crucial action of the hormone during brain development. It is expected that more specific thyroid hormone transporters will be discovered in the near future, which will lead to a better understanding of the tissue-specific regulation of thyroid hormone bioavailability. Specific thyroid hormone transporters may be discovered in the near future, leading to a better understanding of the tissue-specific regulation of thyroid hormone bioavailability.

scholarly journals Identification of Four Novel Variants and Determination of Genotype–Phenotype Correlations for ABCA4 Variants Associated With Inherited Retinal Degenerations

2021 ◽  
Vol 9 ◽  
Author(s):  
Qing Zhu ◽  
Xue Rui ◽  
Ya Li ◽  
Ya You ◽  
Xun-Lun Sheng ◽  
...  
Keyword(s):  
Splice Site Mutation ◽  
Missense Variant ◽  
Cone Dystrophy ◽  
Missense Mutations ◽  
Site Mutation ◽  
Targeted Next Generation Sequencing ◽  
Retinal Degenerations ◽  
Pathogenic Variants ◽  
Physico Chemical ◽  
Type 3

PurposeThe purpose of the study is to describe the genetic and clinical features of 17 patients with ABCA4-related inherited retinal degenerations (IRDs) and define the phenotype–genotype correlations.MethodsIn this multicenter retrospective study, 17 patients from 16 families were enrolled, and ABCA4 gene variants were detected using targeted next-generation sequencing using a custom designed panel for IRDs. Sanger sequencing and co-segregation analysis of the suspected pathogenic variants were performed with the family members. The pathogenicities of variants were evaluated according to the American College of Medical Genetics and Genomics guidelines (ACMG). Protein structure modifications mediated by the variants were studied using bioinformatic analyses.ResultsThe probands were diagnosed with Stargardt disease 1 (7), cone-rod dystrophy type 3 (8), cone dystrophy (1), and retinitis pigmentosa 19 (1). Onset of symptoms occurred between 5 and 27 years of age (median age = 12.4 years). A total of 30 unique ABCA4 suspicious pathogenic variations were observed, including 18 missense mutations, seven frameshift mutations, two nonsense mutations, one canonical splice site mutation, one small in-frame deletion, and one insertion. Four novel ABCA4 variants were identified. Two novel frameshift variants, c.1290dupC (p.W431fs), and c.2967dupT (G990fs), were determined to be pathogenic. A novel missense variant c.G5761T (p.V1921L) was likely pathogenic, and another novel missense c.C170G (p.P57R) variant was of undetermined significance. All ABCA4 variants tested in this study inordinately changed the physico-chemical parameters and structure of protein based on in silico analysis.ConclusionABCA4-related IRD is genetically and clinically highly heterogeneous. Four novel ABCA4 variants were identified. This study will expand the spectrum of disease-causing variants in ABCA4, which will further facilitate genetic counseling.

scholarly journals The Wiskott-Aldrich syndrome and X-linked congenital thrombocytopenia are caused by mutations of the same gene

Blood ◽  
1995 ◽  
Vol 86 (10) ◽  
pp. 3797-3804 ◽  
Author(s):  
Q Zhu ◽  
M Zhang ◽  
RM Blaese ◽  
JM Derry ◽  
A Junker ◽  
...  
Keyword(s):  
Clinical Symptoms ◽  
Point Mutations ◽  
Gene Mutations ◽  
Exon Skipping ◽  
Splice Site Mutation ◽  
Missense Mutations ◽  
Site Mutation ◽  
Exon 2 ◽  
Wiskott Aldrich Syndrome ◽  
Was Gene

The Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by thrombocytopenia, small platelets, eczema, recurrent infections, and immunodeficiency. Besides the classic WAS phenotype, there is a group of patients with congenital X-linked thrombocytopenia (XLT) who have small platelets but only transient eczema, if any, and minimal immune deficiency. Because the gene responsible for WAS has been sequenced, it was possible to correlate the WAS phenotypes with WAS gene mutations. Using a fingerprinting screening technique, we determined the approximate location of the mutation in 13 unrelated WAS patients with mild to severe clinical symptoms. Direct sequence analysis of cDNA and genomic DNA obtained from patient-derived cell lines showed 12 unique mutations distributed throughout the WAS gene, including insertions, deletions, and point mutations resulting in amino acid substitutions, termination, exon skipping, or splicing defects. Of 4 unrelated patients with the XLT phenotype, 3 had missense mutations affecting exon 2 and 1 had a splice-site mutation affecting exon 9. Patients with classic WAS had more complex mutations, resulting in termination codons, frameshift, and early termination. These findings provide direct evidence that XLT and WAS are caused by mutations of the same gene and suggest that severe clinical phenotypes are associated with complex mutations.

scholarly journals Thyroid hormone transporters

2005 ◽  
Vol 33 (1) ◽  
pp. 228-232 ◽  
Author(s):  
E.C.H. Friesema ◽  
J. Jansen ◽  
T.J Visser
Keyword(s):  
Biological Activity ◽  
Thyroid Hormone ◽  
Thyroid Gland ◽  
Cell Membrane ◽  
Human Chromosome ◽  
Elevated Serum ◽  
Psychomotor Retardation ◽  
Follicular Cells ◽  
Serum T3 ◽  
T3 Receptors

Thyroid hormone is important for development of various tissues, in particular brain, and for regulation of metabolic processes throughout life. The follicular cells of the thyroid gland produce predominantly T4 (thyroxine), but the biological activity of thyroid hormone is largely exerted by T3 (3,3′,5-tri-iodothyronine). The deiodinases involved in T4-to-T3 conversion or T4 and T3 degradation, as well as the T3 receptors, are located intracellularly. Therefore the action and metabolism of thyroid hormone require transport of iodothyronines across the cell membrane via specific transporters. Recently, a number of transporters capable of cellular uptake of iodothyronines have been identified. The most specific transporters identified so far are OATP1C1 and MCT8, which appear to be involved in T4 transport across the blood–brain barrier, and in T3 transport into brain neurons, respectively. The MCT8 gene is located on human chromosome Xq13, and mutations in MCT8 are associated with X-linked severe psychomotor retardation and elevated serum T3 levels.

scholarly journals Mice with Impaired Extrathyroidal Thyroxine to 3,5,3′-Triiodothyronine Conversion Maintain Normal Serum 3,5,3′-Triiodothyronine Concentrations

Endocrinology ◽  
2007 ◽  
Vol 148 (3) ◽  
pp. 954-960 ◽  
Author(s):  
Marcelo A. Christoffolete ◽  
Rafael Arrojo e Drigo ◽  
Fernanda Gazoni ◽  
Susana M. Tente ◽  
Vanessa Goncalves ◽  
...  
Keyword(s):  
Biological Effects ◽  
Elevated Serum ◽  
Normal Growth ◽  
Normal Serum ◽  
C3h Mice ◽  
Serum T3 ◽  
Serum T4 ◽  
Hormone Homeostasis ◽  
Type 3

For T3 to mediate its biological effects, the prohormone T4 must be activated by removal of an outer-ring iodine by the type 1 or 2 deiodinases (D1 and D2) with approximately 60% of the daily T3 production in rodents being produced extrathyroidally through this pathway. To further define the role of these enzymes in thyroid hormone homeostasis, we backcrossed the targeted disruption of the Dio2 gene into C3H/HeJ (C3H) mice with genetically low D1 expression to create the C3H-D2KO mouse. Remarkably, these mice maintain euthyroid serum T3 levels with normal growth and no decrease in expression of hepatic T3-responsive genes. However, serum T4 is increased 1.2-fold relative to the already elevated C3H levels, and serum TSH is increased 1.4-fold. Despite these increases, thyroidal 125I uptake indicates no difference in thyroidal activity between C3H-D2KO and C3H mice. Although C3H-D2KO hepatic and renal D1 activities were well below those observed in wild-type mice (∼0.1-fold for both), they were 8-fold and 2-fold higher, respectively, relative to C3H mice. Thyroidal D1 and cerebral cortical type 3 deiodinase activity were unchanged between C3H-D2KO and C3H mice. In conclusion, C3H-D2KO mice have notably elevated serum T4 levels, and this, in conjunction with residual D1 activity, is likely an important role in the maintenance of euthyroid serum T3 concentrations.

scholarly journals Type 3 Deiodinase Deficiency Results in Functional Abnormalities at Multiple Levels of the Thyroid Axis

Endocrinology ◽  
2007 ◽  
Vol 148 (12) ◽  
pp. 5680-5687 ◽  
Author(s):  
Arturo Hernandez ◽  
M. Elena Martinez ◽  
Xiao-Hui Liao ◽  
Jacqueline Van Sande ◽  
Samuel Refetoff ◽  
...  
Keyword(s):  
Wild Type ◽  
Central Hypothyroidism ◽  
Trh Stimulation ◽  
Serum T3 ◽  
Antithyroid Treatment ◽  
Pituitary Glands ◽  
Thyroid Axis ◽  
Type 3 ◽  
Serum Tsh ◽  
Hormonal Levels

The type 3 deiodinase (D3) is a selenoenzyme that inactivates thyroid hormones and is highly expressed during development and in the adult central nervous system. We have recently observed that mice lacking D3 activity (D3KO mice) develop perinatal thyrotoxicosis followed in adulthood by a pattern of hormonal levels that is suggestive of central hypothyroidism. In this report we describe the results of additional studies designed to investigate the regulation of the thyroid axis in this unique animal model. Our results demonstrate that the thyroid and pituitary glands of D3KO mice do not respond appropriately to TSH and TRH stimulation, respectively. Furthermore, after induction of severe hypothyroidism by antithyroid treatment, the rise in serum TSH in D3KO mice is only 15% of that observed in wild-type mice. In addition, D3KO animals rendered severely hypothyroid fail to show the expected increase in prepro-TRH mRNA in the paraventricular nucleus of the hypothalamus. Finally, treatment with T3 results in a serum T3 level in D3KO mice that is much higher than that in wild-type mice. This is accompanied by significant weight loss and lethality in mutant animals. In conclusion, the absence of D3 activity results in impaired clearance of T3 and significant defects in the mechanisms regulating the thyroid axis at all levels: hypothalamus, pituitary, and thyroid.

scholarly journals Evidence for a Homodimeric Structure of Human Monocarboxylate Transporter 8

Endocrinology ◽  
2009 ◽  
Vol 150 (11) ◽  
pp. 5163-5170 ◽  
Author(s):  
W. Edward Visser ◽  
Nancy J. Philp ◽  
Thamar B. van Dijk ◽  
Wim Klootwijk ◽  
Edith C. H. Friesema ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Psychomotor Retardation ◽  
Monocarboxylate Transporter ◽  
Membrane Association ◽  
Transport Function ◽  
Wild Type ◽  
Transfected Cells ◽  
Physiological Relevance ◽  
Dimerization Process

The human monocarboxylate transporter 8 (hMCT8) protein mediates transport of thyroid hormone across the plasma membrane. Association of hMCT8 mutations with severe psychomotor retardation and disturbed thyroid hormone levels has established its physiological relevance, but little is still known about the basic properties of hMCT8. In this study we present evidence that hMCT8 does not form heterodimers with the ancillary proteins basigin, embigin, or neuroplastin, unlike other MCTs. In contrast, it is suggested that MCT8 exists as monomer and homodimer in transiently and stably transfected cells. Apparently hMCT8 forms stable dimers because the complex is resistant to denaturing conditions and dithiothreitol. Cotransfection of wild-type hMCT8 with a mutant lacking amino acids 267–360 resulted in formation of homo-and heterodimers of the variants, indicating that transmembrane domains 4–6 are not involved in the dimerization process. Furthermore, we explored the structural and functional role of the 10 Cys residues in hMCT8. All possible Cys>Ala mutants did not behave differently from wild-type hMCT8 in protein expression, cross-linking experiments with HgCl2 and transport function. Our findings indicate that individual Cys residues are not important for the function of hMCT8 or suggest that hMCT8 has other yet-undiscovered functions in which cysteines play an essential role.

scholarly journals Genotype-Phenotype Relationship in Patients with Mutations in Thyroid Hormone Transporter MCT8

Endocrinology ◽  
2008 ◽  
Vol 149 (5) ◽  
pp. 2184-2190 ◽  
Author(s):  
Jurgen Jansen ◽  
Edith C. H. Friesema ◽  
Monique H. A. Kester ◽  
Charles E. Schwartz ◽  
Theo J. Visser
Keyword(s):  
Plasma Membrane ◽  
Thyroid Hormone ◽  
Protein Expression ◽  
Elevated Serum ◽  
Monocarboxylate Transporter ◽  
Psychomotor Development ◽  
Substrate Affinity ◽  
Loss Of Function ◽  
Wild Type ◽  
Rt Pcr

Loss-of-function mutations in thyroid hormone transporter monocarboxylate transporter 8 (MCT8) lead to severe X-linked psychomotor retardation and elevated serum T3 levels. Most patients, for example those with mutations V235M, S448X, insI189, or delF230, cannot stand, walk, or speak. Patients with mutations L434W, L568P, and S194F, however, walk independently and/or develop some dysarthric speech. To study the relationship between mutation and phenotype, we transfected JEG3 and COS1 cells with wild-type or mutant MCT8. Expression and function of the transporter were studied by analyzing T3 and T4 uptake, T3 metabolism (by cotransfected type 3 deiodinase), Western blotting, affinity labeling with N-bromoacetyl-T3, immunocytochemistry, and quantitative RT-PCR. Wild-type MCT8 increased T3 uptake and metabolism about 5-fold compared with empty vector controls. Mutants V235M, S448X, insI189, and delF230 did not significantly increase transport. However, S194F, L568P, and L434W showed about 20, 23, and 37% of wild-type activity. RT-PCR did not show significant differences in mRNA expression between wild-type and mutant MCT8. Immunocytochemistry detected the nonfunctional mutants V235M, insI189, and delF230 mostly in the cytoplasm, whereas mutants with residual function were expressed at the plasma membrane. Mutants S194F and L434W showed high protein expression but low affinity for N-bromoacetyl-T3; L568P was detected in low amounts but showed relatively high affinity. Mutations in MCT8 cause loss of function through reduced protein expression, impaired trafficking to the plasma membrane, or reduced substrate affinity. Mutants L434W, L568P, and S194F showed significant residual transport capacity, which may underlie the more advanced psychomotor development observed in patients with these mutations.

scholarly journals A founder splice site mutation underlies glycogen storage disease type 3 in consanguineous Saudi families

2014 ◽  
Vol 34 (5) ◽  
pp. 390-395 ◽  
Author(s):  
Sulman Basit ◽  
Omhani Malibari ◽  
Alia Mahmood Al Balwi ◽  
Firoz Abdusamad ◽  
Feras Abu Ismail
Keyword(s):  
Glycogen Storage Disease ◽  
Splice Site ◽  
Storage Disease ◽  
Splice Site Mutation ◽  
Glycogen Storage Disease Type ◽  
Glycogen Storage ◽  
Disease Type ◽  
Site Mutation ◽  
Type 3

scholarly journals The mutational spectrum of Hunter syndrome reveals correlation between biochemical and clinical profiles in Tunisian patients

2020 ◽  
Author(s):  
latifa chkioua ◽  
Oussama Grissa ◽  
Nadia Leban ◽  
Moez Gribaa ◽  
Hela Boudabous ◽  
...  
Keyword(s):  
Nonsense Mutation ◽  
Dermatan Sulfate ◽  
Splice Site Mutation ◽  
Hunter Syndrome ◽  
Molecular Testing ◽  
Missense Mutations ◽  
Lysosomal Storage ◽  
High Concentration ◽  
Site Mutation ◽  
Mps Ii

Abstract Background: Mucopolysaccharidosis type II (MPS II) or Hunter syndrome is an X-linked recessive lysosomal storage disorder resulting from deficient activity of iduronate 2-sulfatase (IDS) and the progressive lysosomal accumulation of sulfated glycosaminoglycans (GAGs). Methods: A diagnosis of MPS II or Hunter syndrome was performed based on the following approach after a clinical and paraclinical suspicion. Two biochemical and molecular tests were carried out separately and according to the availability of the biological material. Results: All patients in this cohort presented the most common MPS II clinical features. Electrophoresis of GAGs on a cellulose acetate plate in the presence of a high concentration of heparane sulfate showed an abnormal dermatan sulfate band in the patients compared with that in a control case. Furthermore, leukocyte IDS activity ranged from 0.00 to 0.75 nmol/h/mg of leukocyte protein in patients.Five previously reported mutations were identified in this study patients: one splice site mutation, c.240+1G>A; two missense mutations, p.R88P and p.G94D; a large deletion of exon 1 to exon 7; and one nonsense mutation, p.Q396*. In addition, two novel alterations were identified in the MPS II patients: one frame shift mutation, p.D450Nfs*95 and one nonsense mutation, p.Q204*. Additionally, five known IDS polymorphisms were identified in the patients: c.419-16 delT, c.641C>T (p.T214M), c.438 C>T (p.T146T), c.709-87G>A, and c.1006+38T>C.Conclusions: The high level of urine GAGs and the deficiency of iduronate 2-sulfatase activity was associated with the phenotype expression of Hunter syndrome. Molecular testing was useful for the patients’ phenotypic classification and the detection of carriers.

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