Clinical and functional consequences of C-terminal variants in MCT8

CONTEXT: Genetic variants in SLC16A2, encoding the thyroid hormone transporter MCT8, can cause intellectual and motor disability and abnormal serum thyroid function tests, known as MCT8 deficiency. The C-terminal domain of MCT8 is poorly conserved, which complicates prediction of the deleteriousness of variants in this region. We studied the functional consequences of 5 novel variants within this domain and their relation to the clinical phenotypes. METHODS: We enrolled male subjects with intellectual disability in whom genetic variants were identified in exon 6 of SLC16A2. The impact of identified variants was evaluated in transiently transfected cell lines and patient-derived fibroblasts. RESULTS: Seven individuals from 5 families harbored potentially deleterious variants affecting the C-terminal domain of MCT8. Two boys with clinical features considered atypical for MCT8 deficiency had a missense variant [c.1724A>G;p.(His575Arg) or c.1796A>G;p.(Asn599Ser)] that did not affect MCT8 function in transfected cells or patient-derived fibroblasts, challenging a causal relationship. Two brothers with classical MCT8 deficiency had a truncating c.1695delT;p.(Val566*) variant that completely inactivated MCT8 in vitro. The 3 other boys had relatively less-severe clinical features and harbored frameshift variants that elongate the MCT8 protein [c.1805delT;p.(Leu602HisfsTer680) and c.del1826-1835;p.(Pro609GlnfsTer676)] and retained ~50% residual activity. Additional truncating variants within transmembrane domain 12 were fully inactivating, whereas those within the intracellular C-terminal tail were tolerated. CONCLUSIONS: Variants affecting the intracellular C-terminal tail of MCT8 are likely benign unless they cause frameshifts that elongate the MCT8 protein. These findings provide clinical guidance in the assessment of the pathogenicity of variants within the C-terminal domain of MCT8

Nutritional Status and Body Composition in Patients With Hepatic Glycogen Storage Diseases Treated With Uncooked Cornstarch—A Controlled Study

Hepatic glycogen storage diseases (GSDs) are genetic diseases associated with fasting hypoglycemia. Periodic intake of uncooked cornstarch is one of the treatment strategies available for those disorders. For reasons that are still not clear, patients with hepatic GSDs may be overweight. Aims: To assess nutritional status and body composition in patients with hepatic GSDs receiving uncooked cornstarch. Methods: The sample included 25 patients with hepatic GSD (type Ia = 14; Ib = 6; III = 3; IXα = 1; IXβ = 1), with a median age of 11.0 years (interquartile range [IQR] = 9.0-17.5), matched by age and gender with 25 healthy controls (median age = 12.0 years, IQR = 10.0-17.5). Clinical, biochemical, and treatment-related variables were obtained from medical records. Nutritional status and body composition were prospectively evaluated by bioelectrical impedance. Results: Patients and controls did not differ with regard to age and gender. Height was significantly reduced in patients (median = 1.43 m, IQR = 1.25-1.54) in comparison to controls (median = 1.54 m, IQR = 1.42-1.61; P = .04). Body mass index for age z -score and fat mass percentage were higher in patients (median = 1.84, IQR = 0.55-3.06; and 27.5%, IQR = 22.6-32.0, respectively) than in controls (median = 0.86, IQR = −0.55 to 1.82; P = .04 and 21.1%, IQR = 13.0-28.3; P = .01, respectively). When patients were stratified by type, those with GSD Ia had significantly higher adiposity (median fat mass = 28.7%, IQR = 25.3-32.9) than those with GSD III and GSD IXα/β (median fat mass = 20.9%, IQR = 14.9-22.6; P = .02). Conclusions: Our findings suggest that patients with hepatic GSD on treatment with cornstarch, especially those with GSD Ia, exhibit abnormalities in nutritional status and body composition, such as short stature and a trend toward overweight and obesity

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Molecular analysis of TSC1 and TSC2 genes and phenotypic correlations in Brazilian families with tuberous sclerosis

Tuberous sclerosis complex (TSC) is an autosomal dominant multisystem disorder characterized by the development of multiple hamartomas in many organs and tissues. It occurs due to inactivating mutations in either of the two genes, TSC1 and TSC2, following a second hit in a tumor suppressor gene in most hamartomas. Comprehensive screening for mutations in both the TSC1 and TSC2 loci has been performed in several cohorts of patients and a broad spectrum of pathogenic mutations have been described. In Brazil, there is no data regarding incidence and prevalence of tuberous sclerosis and mutations in TSC1 and TSC2. We analyzed both genes in 53 patients with high suspicion of tuberous sclerosis using multiplex-ligation dependent probe amplification and a customized next generation sequencing panel. Confirmation of all variants was done by the Sanger method. We identified 50 distinct variants in 47 (89%) of the patients. Five were large rearrangements and 45 were point mutations. The symptoms presented by our series of patients were not different between male and female individuals, except for the more common occurrence of shagreen patch in women (p = 0.028). In our series, consistent with other studies, TSC2 mutations were associated with a more severe phenotypic spectrum than TSC1 mutations. This is the first study that sought to characterize the molecular spectrum of Brazilian individuals with tuberous sclerosis1210CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFundo de Incentivo a Pesquisa e Eventos (FIPE) of Hospital de Clinicas de Porto Alegre; Institute do Cancer Infantil (ICI

Families with a likely benign or variant of uncertain significance in <i>TSC1</i> and <i>TSC</i>.

<p>Families with a likely benign or variant of uncertain significance in <i>TSC1</i> and <i>TSC</i>.</p

Molecular analysis of <i>TSC1</i> and <i>TSC2</i> genes and phenotypic correlations in Brazilian families with tuberous sclerosis

<div><p>Tuberous sclerosis complex (TSC) is an autosomal dominant multisystem disorder characterized by the development of multiple hamartomas in many organs and tissues. It occurs due to inactivating mutations in either of the two genes, <i>TSC1</i> and <i>TSC2</i>, following a second hit in a tumor suppressor gene in most hamartomas. Comprehensive screening for mutations in both the <i>TSC1</i> and <i>TSC2</i> loci has been performed in several cohorts of patients and a broad spectrum of pathogenic mutations have been described. In Brazil, there is no data regarding incidence and prevalence of tuberous sclerosis and mutations in <i>TSC1</i> and <i>TSC2</i>. We analyzed both genes in 53 patients with high suspicion of tuberous sclerosis using multiplex-ligation dependent probe amplification and a customized next generation sequencing panel. Confirmation of all variants was done by the Sanger method. We identified 50 distinct variants in 47 (89%) of the patients. Five were large rearrangements and 45 were point mutations. The symptoms presented by our series of patients were not different between male and female individuals, except for the more common occurrence of shagreen patch in women (p = 0.028). In our series, consistent with other studies, <i>TSC2</i> mutations were associated with a more severe phenotypic spectrum than <i>TSC1</i> mutations. This is the first study that sought to characterize the molecular spectrum of Brazilian individuals with tuberous sclerosis.</p></div

Phenotypic comparison between male and female individuals with TSC.

<p>Phenotypic comparison between male and female individuals with TSC.</p