Allan-Herndon-Dudley syndrome in a female patient and related mechanisms.
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ABSTRACT:
SUBMITTER: Olivati C
PROVIDER: S-EPMC9248228 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Thyroid hormone is essential for the proper development and function of the brain. The active form of thyroid hormone is T(3), which binds to nuclear receptors. Recently, a transporter specific for T(3), MCT8 (monocarboxylate transporter 8) was identified. MCT8 is highly expressed in liver and brain. The gene is located in Xq13 and mutations in MCT8 are responsible for an X-linked condition, Allan-Herndon-Dudley syndrome (AHDS). This syndrome is characterized by congenital hypotonia that progresses to spasticity with severe psychomotor delays. Affected males also present with muscle hypoplasia, generalized muscle weakness, and limited speech. Importantly, these patients have elevated serum levels of free T(3), low to below normal serum levels of free T(4), and levels of thyroid stimulating hormone that are within the normal range. This constellation of measurements of thyroid function enables quick screening for AHDS in males presenting with cognitive impairment, congenital hypotonia, and generalized muscle weakness.
| S-EPMC2094733 | biostudies-literature
Project description:Allan-Herndon-Dudley syndrome (AHDS) is an X-linked disorder caused by impaired thyroid hormone transporter. Patients with AHDS usually exhibit severe motor developmental delay, delayed myelination of the brain white matter, and elevated T3 levels in thyroid tests. Neurological examination of two patients with neurodevelopmental delay revealed generalized hypotonia, and not paresis, as the main neurological finding. Nystagmus and dyskinesia were not observed. Brain magnetic resonance imaging demonstrated delayed myelination in early childhood in both patients. Nevertheless, matured myelination was observed at 6 years of age in one patient. Although the key finding for AHDS is elevated free T3, one of the patients showed a normal T3 level in childhood, misleading the diagnosis of AHDS. Genetic analysis revealed two novel SLC16A2 mutations, p.(Gly122Val) and p.(Gly221Ser), confirming the AHDS diagnosis. These results indicate that AHDS diagnosis is sometimes challenging owing to clinical variability among patients.
| S-EPMC4995413 | biostudies-literature
Project description:Allan-Herndon-Dudley syndrome (AHDS) is a neurodevelopmental disorder that manifests as intellectual disability and motor developmental delay. Thyroid hormone transporter dysfunction due to SLC16A2 mutation is the underlying cause of this disorder. We identified a novel (P537del) and a recurrent (A150V) SLC16A2 mutation in Japanese AHDS patients from two different families. A150V co-segregated with S33P. Both patients showed similar clinical features including severe neurological features and delayed myelination. Thyroid function showed a common finding of elevated T3 levels. No clear genotype-phenotype correlation was observed in patients with SLC16A2 alterations.
| S-EPMC4785542 | biostudies-literature
Project description:Allan-Herndon-Dudley syndrome was among the first of the X-linked mental retardation syndromes to be described (in 1944) and among the first to be regionally mapped on the X chromosome (in 1990). Six large families with the syndrome have been identified, and linkage studies have placed the gene locus in Xq13.2. Mutations in the monocarboxylate transporter 8 gene (MCT8) have been found in each of the six families. One essential function of the protein encoded by this gene appears to be the transport of triiodothyronine into neurons. Abnormal transporter function is reflected in elevated free triiodothyronine and lowered free thyroxine levels in the blood. Infancy and childhood in the Allan-Herndon-Dudley syndrome are marked by hypotonia, weakness, reduced muscle mass, and delay of developmental milestones. Facial manifestations are not distinctive, but the face tends to be elongated with bifrontal narrowing, and the ears are often simply formed or cupped. Some patients have myopathic facies. Generalized weakness is manifested by excessive drooling, forward positioning of the head and neck, failure to ambulate independently, or ataxia in those who do ambulate. Speech is dysarthric or absent altogether. Hypotonia gives way in adult life to spasticity. The hands exhibit dystonic and athetoid posturing and fisting. Cognitive development is severely impaired. No major malformations occur, intrauterine growth is not impaired, and head circumference and genital development are usually normal. Behavior tends to be passive, with little evidence of aggressive or disruptive behavior. Although clinical signs of thyroid dysfunction are usually absent in affected males, the disturbances in blood levels of thyroid hormones suggest the possibility of systematic detection through screening of high-risk populations.
| S-EPMC1226193 | biostudies-literature
Project description:IntroductionA mathematical model of the pituitary-thyroid feedback loop is extended to deepen the understanding of the Allan-Herndon-Dudley syndrome (AHDS). The AHDS is characterized by unusual thyroid hormone concentrations and a mutation in the SLC16A2 gene encoding for the monocarboxylate transporter 8 (MCT8). This mutation leads to a loss of thyroid hormone transport activity. One hypothesis to explain the unusual hormone concentrations of AHDS patients is that due to the loss of thyroid hormone transport activity, thyroxine (T 4) is partially retained in thyroid cells.MethodsThis hypothesis is investigated by extending a mathematical model of the pituitary-thyroid feedback loop to include a model of the net effects of membrane transporters such that the thyroid hormone transport activity can be considered. A nonlinear modeling approach based on the Michaelis-Menten kinetics and its linear approximation are employed to consider the membrane transporters. The unknown parameters are estimated through a constrained parameter optimization.ResultsIn dynamic simulations, damaged membrane transporters result in a retention of T 4 in thyroid cells and ultimately in the unusual hormone concentrations of AHDS patients. The Michaelis-Menten modeling approach and its linear approximation lead to similar results.DiscussionThe results support the hypothesis that a partial retention of T 4 in thyroid cells represents one mechanism responsible for the unusual hormone concentrations of AHDS patients. Moreover, our results suggest that the retention of T 4 in thyroid cells could be the main reason for the unusual hormone concentrations of AHDS patients.
| S-EPMC9772020 | biostudies-literature
Project description:BackgroundAllan-Herndon-Dudley syndrome (AHDS) is an X-linked recessive neurodegenerative disorder caused by mutations in the SLC16A2 gene that encodes thyroid hormone transporter. AHDS has been rarely reported in China.Case presentationThis study reported a novel splicing mutation in the SLC16A2 gene in an 18-month-old male patient with AHDS. The patient was born to non-consanguineous, healthy parents of Chinese origin. He passed new-born screening for hypothyroidism, but failed to reach developmental milestones. He presented with hypotonia, severe mental retardation, dysarthria and ataxia. Genetic analysis identified a novel splicing mutation, NM_006517.4: c.431-2 A > G, in the SLC16A2 gene inherited from his mother. The patient received Triac treatment, (triiodothyroacetic acid), a thyroid hormone analogue for 3 months. Triac treatment effectively reduced serum TSH concentrations and normalized serum T3 concentrations in the patient.ConclusionsThis study reported the first case of AHDS treated by Triac in China. And the study expanded the mutational spectrum of the SLC16A2 gene in AHDS patients.
| S-EPMC8981932 | biostudies-literature
Project description:Mutations in the thyroid hormone (TH) transporter MCT8 have been identified as the cause for Allan-Herndon-Dudley Syndrome (AHDS), characterized by severe psychomotor retardation and altered TH serum levels. Here we report a novel MCT8 mutation identified in 4 generations of one family, and its functional characterization.Proband and family members were screened for 60 genes involved in X-linked cognitive impairment and the MCT8 mutation was confirmed. Functional consequences of MCT8 mutations were studied by analysis of [125I]TH transport in fibroblasts and transiently transfected JEG3 and COS1 cells, and by subcellular localization of the transporter.The proband and a male cousin demonstrated clinical findings characteristic of AHDS. Serum analysis showed high T3, low rT3, and normal T4 and TSH levels in the proband. A MCT8 mutation (c.869C>T; p.S290F) was identified in the proband, his cousin, and several female carriers. Functional analysis of the S290F mutant showed decreased TH transport, metabolism and protein expression in the three cell types, whereas the S290A mutation had no effect. Interestingly, both uptake and efflux of T3 and T4 was impaired in fibroblasts of the proband, compared to his healthy brother. However, no effect of the S290F mutation was observed on TH efflux from COS1 and JEG3 cells. Immunocytochemistry showed plasma membrane localization of wild-type MCT8 and the S290A and S290F mutants in JEG3 cells.We describe a novel MCT8 mutation (S290F) in 4 generations of a family with Allan-Herndon-Dudley Syndrome. Functional analysis demonstrates loss-of-function of the MCT8 transporter. Furthermore, our results indicate that the function of the S290F mutant is dependent on cell context. Comparison of the S290F and S290A mutants indicates that it is not the loss of Ser but its substitution with Phe, which leads to S290F dysfunction.
| S-EPMC4591285 | biostudies-literature
Project description:Allan-Herndon-Dudley Syndrome (AHDS), an X linked condition, is characterized by congenital hypotonia that progresses to spasticity with severe psychomotor delays, in combination with altered thyroid hormone levels, in particular, high serum T3 levels. Recently, this disease was proved to be caused by mutations in SLC16A2 coding for the monocarboxylate thyroid hormone transporter 8 (MCT8). Here we describe a 26-year -old Japanese patient with AHDS who had deletion of exon 3 of SLC16A2.
| S-EPMC3809735 | biostudies-literature
Project description:We report a novel 1 bp deletion (c.1834delC) in the MCT8 gene in a large Brazilian family with Allan-Herndon-Dudley syndrome (AHDS), an X linked condition characterised by severe mental retardation and neurological dysfunction. The c.1834delC segregates with the disease in this family and it was not present in 100 control chromosomes, further confirming its pathogenicity. This mutation causes a frameshift and the inclusion of 64 additional amino acids in the C-terminal region of the protein. Pathogenic mutations in the MCT8 gene, which encodes a thyroid hormone transporter, results in elevated serum triiodothyronine (T3) levels, which were confirmed in four affected males of this family, while normal levels were found among obligate carriers. Through in vitro functional assays, we showed that this mutation decreases cellular T3 uptake and intracellular T3 metabolism. Therefore, the severe neurological defects present in the patients are due not only to deficiency of intracellular T3, but also to altered metabolism of T3 in central neurones. In addition, the severe muscle hypoplasia observed in most AHDS patients may be a consequence of high serum T3 levels.
| S-EPMC2649011 | biostudies-literature
Project description:Patients with mutations in the thyroid hormone (TH) cell transporter MCT8 gene develop severe neuropsychomotor retardation known as the Allan-Herndon-Dudley syndrome (AHDS). It is assumed that this is caused by a reduction in TH signaling in the developing brain during both intrauterine and postnatal developmental stages, and treatment remains understandably challenging. Given species differences in brain TH transporters and the limitations of studies in mice, we generated cerebral organoids (COs) using human iPSCs from MCT8-deficient patients. We found that MCT8-deficient COs exhibit (i) alterations in early neurodevelopment, resulting in smaller neural rosettes with thinner cortical units, (ii) impaired T3 transport in developing neural cells, as assessed through deiodinase-3-mediated T3 catabolism, (iii) reduced expression of genes involved in cerebral cortex development, and (iv) reduced T3-inducibility of TH-regulated genes. In contrast, the TH-analogs 3,5-diiodothyropropionic acid and 3,3’,5-triiodothyroacetic acid triggered normal responses (induction/repression of T3-responsive genes) in MCT8-deficient COs, constituting a proof-of-concept that lack of T3 transport underlies the pathophysiology of AHDS, and demonstrating the clinical potential for TH analogues to be used in treating AHDS patients. MCT8-deficient COs represent a species-specific relevant preclinical model that can be utilized to screen drugs with potential benefits as personalized therapeutics for AHDS patients.
2024-03-11 | GSE253412 | GEO