We report a family with X-linked mental retardation that has a novel mutation in the monocarboxylate transporter 8 (MCT8) gene associated with a characteristic neurodevelopmental phenotype with early childhood hypotonia that progresses to spasticity and global developmental delays. Affected patients experience moderate to severe psychomotor delays and congenital hypotonia, develop a myopathic facies, have diminished muscle bulk and generalized muscle weakness, develop progressive spasticity and movement disorders, and have limited speech but alert, affable personalities. Acquired microcephaly and abnormal myelination on brain magnetic resonance imaging can be present. Normal monocarboxylate transporter 8 gene functioning appears to be necessary for normal thyroid-associated metabolism in neurons. Abnormal thyroid function tests appear to be a consistent finding in the absence of typical signs of thyroid dysfunction. Although the phenotype appears to be consistent, and although the neurotoxic effects of abnormal central and peripheral neuromuscular system thyroid metabolism might be partly or wholly responsible for the neurologic phenotype reported, the exact mechanism remains unclear.
"In addition to the clinical and biological features of patients with SLC16A2 mutations, some authors have reported a nonspecific myelination delay [Holden et al., 2005; Namba et al., 2008] and spectroscopic abnormalities [Sijens et al., 2008]. More recently, the identification of SLC16A2 mutations in a series of patients initially considered as presenting with a severe Pelizaeus–Merzbacher-like disease (PMD) in their first years of life has confirmed this association with delayed myelination [Gika et al., 2010; Vaurs - Barrì ere et al., 2009] . "
[Show abstract][Hide abstract] ABSTRACT: SLC16A2, the gene for the 2(nd) member of the solute carrier family 16 (monocarboxylic acid transporter), located on chromosome Xq13.2, encodes a very efficient thyroid hormone (TH) transporter: monocarboxylate transporter 8, MCT8. Its loss of function is responsible in males for a continuum of psychomotor retardation ranging from severe (no motor acquisition, no speech) to mild (ability to walk with help and a few words of speech). Triiodothyronine uptake measurement in transfected cells and, more recently, patient fibroblasts, has been described to study the functional consequences of MCT8 mutations. Here we describe 3 novel MCT8 mutations, including one missense variation not clearly predicted to be damaging but found in a severely affected patient. Functional studies in fibroblasts and JEG3 cells demonstrate the usefulness of both cellular models in validating the deleterious effects of a new MCT8 mutation if there is still a doubt as to its pathogenicity. Moreover, the screening of fibroblasts from a large number of patient fibroblasts and of transfected mutations has allowed us to demonstrate that JEG3 transfected cells are more relevant than fibroblasts in revealing a genotype-phenotype correlation.
Human Mutation 07/2013; 34(7). DOI:10.1002/humu.22331 · 5.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Iterative feedback tuning (IFT) is a data-based method for the tuning of restricted complexity controllers. At each iteration, an update for the parameters of the controller is estimated from data obtained partly from the normal operation of the closed loop system and partly from a special experiment. The choice of a prefilter for the input data to the special experiment is a degree of freedom of the method. In the present contribution, the prefilter is designed in order to enhance the accuracy of the IFT update.
Decision and Control, 2003. Proceedings. 42nd IEEE Conference on; 01/2004
[Show abstract][Hide abstract] ABSTRACT: The actions and the metabolism of thyroid hormone are intracellular events that require the transport of iodothyronines across the plasma membrane. It is increasingly clear that this process does not occur by simple diffusion, but is facilitated by transport proteins. Only recently have iodothyronine transporters been identified at the molecular level, of which organic anion transporting polypeptide 1C1 and monocarboxylate transporter 8 (MCT8) deserve special mention, because of their high activity and specificity for iodothyronines. Organic anion transporting polypeptide 1C1 is almost exclusively expressed in brain capillaries, and may be crucial for the transport of the prohormone T4 across the blood-brain barrier. MCT8 is also expressed in the brain--in particular, in neurons--but also in other tissues. MCT8 seems to be especially important for the uptake of active hormone T3 into neurons, which is essential for optimal brain development. T3 is produced from T4 by type 2 deiodinase in neighboring astrocytes. Neurons express type 3 deiodinase, the enzyme that terminates T3 activity. The SLC16A2 (formerly MCT8) gene is located on chromosome Xq13.2 and has recently been associated with a syndrome combining severe, X-linked, psychomotor retardation and high serum T3 levels. In over 20 families, where affected males have developed this syndrome, several mutations in MCT8 have been identified. The disease mechanism is thought to involve a defect in the neuronal entry of T3 and, therefore, in the action and metabolism of T3 in these cells. This defect results in impaired neurological development and a decrease in T3 clearance.
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