Functional analysis of monocarboxylate transporter 8 mutations identified in patients with X-linked psychomotor retardation and elevated serum triiodothyronine.

CONTEXT: T(3) action in neurons is essential for brain development. Recent evidence indicates that monocarboxylate transporter 8 (MCT8) is important for neuronal T(3) uptake. Hemizygous mutations have been identified in the X-linked MCT8 gene in boys with severe psychomotor retardation and elevated serum T(3) levels. OBJECTIVE: The objective of this study was to determine the functional consequences of MCT8 mutations regarding transport of T(3). DESIGN: MCT8 function was studied in wild-type or mutant MCT8-transfected JEG3 cells by analyzing: 1) T(3) uptake, 2) T(3) 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 T(3) levels in these patients are caused by inactivation of the MCT8 transporter, preventing action and metabolism of T(3) in central neurons.

Seasonality of diagnosis of type 1 diabetes mellitus in the Netherlands (Young Dudes-2).

BACKGROUND: The aim of this study was to investigate seasonality in the initial presentation of type 1 diabetes mellitus (T1DM) among Dutch children. METHODS: Observational, nationwide study in the Netherlands. Using the national registry for both healthcare reimbursement and pharmaceutical care, data of all Dutch children (aged 0-14 years) with a diagnosis of T1DM in the period 2009-2011 were obtained. RESULTS: During the study period (2009-2011) an average annual number of 2.909.537 children aged 0-14 lived in the Netherlands and 676 children were diagnosed with T1DM per year, translating into an annual incidence rate (IR) of T1DM of 23.2 per hundred thousand children (ptc). The annual IR differed significantly (p=0.03) between seasons: 6.4 ptc in winter, 4.9 ptc in spring, 5.4 ptc in summer and 6.6 ptc in autumn. This pattern was present within both boys and girls Conclusions: Among Dutch children aged 0-14 years, there is seasonality in the of T1DM with a peak incidence in autumn and winter.

Association between mutations in a thyroid hormone transporter and severe X-linked psychomotor retardation.

Monocarboxylate transporter 8 (MCT8) is a thyroid hormone transporter, the gene of which is located on the X chromosome. We tested whether mutations in MCT8 cause severe psychomotor retardation and high serum triiodothyronine (T3) concentrations in five unrelated young boys. The coding sequence of MCT8 was analysed by PCR and direct sequencing of its six exons. In two patients, gene deletions of 2.4 kb and 24 kb were recorded and in three patients missense mutations Ala150Val, Arg171 stop, and Leu397Pro were identified. We suggest that this novel syndrome of X-linked psychomotor retardation is due to a defect in T3 entry into neurons through MCT8, resulting in impaired T3 action and metabolism.

Adult height after long-term, continuous growth hormone (GH) treatment in short children born small for gestational age: results of a randomized, double-blind, dose-response GH trial.

The GH dose-response effect of long-term continuous GH treatment on adult height (AH) was evaluated in 54 short children born small for gestational age (SGA) who were participating in a randomized, double-blind, dose-response trial. Patients were randomly and blindly assigned to treatment with either 3 IU (group A) or 6 IU (group B) GH/m(2).d ( approximately 0.033 or 0.067 mg/kg.d, respectively). The mean (+/-SD) birth length was -3.6 (1.4), the age at the start of the study was 8.1 (1.9) yr, and the height SD score (SDS) at the start of the study -3.0 (0.7). Seventeen of the 54 children were partially GH deficient (stimulated GH peak, 10-20 mU/liter). Fifteen non-GH-treated, non-GH-deficient, short children born SGA, with similar inclusion criteria, served as controls [mean (+/-SD) birth length, -3.3 (1.2); age at start, 7.8 (1.7) yr; height SDS at start, -2.6 (0.5)]. GH treatment resulted in an AH above -2 SDS in 85% of the children after a mean (+/-SD) GH treatment period of 7.8 (1.7) yr. The mean (SD) AH SDS was -1.1 (0.7) for group A and -0.9 (0.8) for group B, resulting from a mean (+/-SD) gain in height SDS of 1.8 (0.7) for group A and 2.1 (0.8) for group B. No significant differences between groups A and B were found for AH SDS (mean difference, 0.3 SDS; 95% confidence interval, -0.2, 0.6; P > 0.2) and gain in height SDS (mean difference, 0.3 SDS; 95% confidence interval, -0.1, 0.7; P > 0.1). When corrected for target height, the mean corrected AH SDS was -0.2 (0.8) for group A and -0.4 (0.9) for group B. The mean (+/-SD) AH SDS of the control group [-2.3 (0.7)] was significantly lower than that of the GH-treated group (P < 0.001). Multiple regression analysis indicated the following predictive variables for AH SDS: target height SDS, height SDS, and chronological age minus bone age (years) at the start of the study. GH dose had no significant effect. In conclusion, long-term continuous GH treatment in short children born SGA without signs of persistent catch-up growth leads to a normalization of AH, even with a GH dose of 3 IU/m(2).d ( approximately 0.033 mg/kg.d).

Effect of discontinuation of growth hormone treatment on risk factors for cardiovascular disease in adolescents born small for gestational age.

Hyperlipidemia, diabetes mellitus type 2, and coronary heart disease have been associated with being born small for gestational age (SGA). It has been reported that GH treatment induced higher insulin levels, which has led to concern regarding the long-term effect of GH treatment in predisposed individuals such as children born SGA. In this study, we assessed the effect of discontinuation of long-term GH treatment in 47 adolescents born SGA on oral glucose tolerance tests, blood pressure (BP), and serum lipid levels for two GH dosage groups (3 vs. 6 IU/m2 x d). At 6 months after discontinuation of GH treatment mean (SD) age was 16.0 (2.1) yr. Mean duration of GH treatment had been 6.9 (1.5) yr. Fasting glucose levels and 120-min area under the curve for glucose 6 months after discontinuation of GH treatment showed no difference from pretreatment levels for both GH dosage groups. After discontinuation of GH treatment, fasting insulin levels returned to pretreatment levels (8.4 mU/liter), whereas the 120-min area under the curve for insulin decreased, compared with 6-yr levels (P < 0.01), regardless of GH dosage group. No significant difference was found when levels were compared with a control group. In addition, for both GH dosage groups, no significant changes in systolic and diastolic BP SD score, total cholesterol, and atherogenic index (total cholesterol/high-density lipoprotein cholesterol) were seen from 6 yr of GH until 6 months after discontinuation of GH treatment. In conclusion, in children born SGA, the GH-induced insulin insensitivity disappeared after discontinuation of GH, even after long-term GH treatment. Furthermore, the beneficial effect of GH on BP was not changed after discontinuation of GH, and most children had normal lipid levels.

Long-term effects of growth hormone (GH) treatment on body composition and bone mineral density in short children born small-for-gestational-age: six-year follow-up of a randomized controlled GH trial.

UNLABELLED: Context Alterations in the GH-IGF-I axis in short small-for-gestational-age (SGA) children might be associated with abnormalities in bone mineral density (BMD) and body composition. In addition, birth weight has been inversely associated with diabetes and cardiovascular disease in adult life. Data on detailed body composition in short SGA children and long-term effects of GH treatment are very scarce. OBJECTIVE: To investigate effects of long-term GH treatment on body composition and BMD by dual energy X-ray absorptiometry (DXA) in short SGA children. DESIGN: Longitudinal 6-year GH study with a randomized controlled part for 3 years. RESULTS: At baseline, fat percentage standard deviation score (SDS) and lumbar spine BMD SDS corrected for height (BMAD(LS) SDS) were significantly lower than zero. Lean body mass (LBM) SDS adjusted for age was also reduced, but LBM adjusted for height (LBM SDS(height)) was not decreased. GH treatment induced a decrease in fat percentage SDS and an increase in BMAD(LS) SDS. LBM SDS(height) remained similar in GH-treated children, but deteriorated in untreated controls. When these untreated controls subsequently started GH treatment, their LBM SDS(height) rapidly normalized to values comparable with zero. CONCLUSION: During long-term GH treatment in short SGA children, fat percentage SDS decreased and BMAD(LS) SDS increased. These effects of GH treatment were most prominent in children who started treatment at a younger age and in those with greater height gain during GH treatment. LBM SDS(height )remained around 0 SDS in GH-treated children, but declined to low normal values in untreated controls.