Whole genome SNP genotyping and exome sequencing reveal novel genetic variants and putative causative genes in congenital hyperinsulinism.

Congenital hyperinsulinism of infancy (CHI) is a rare disorder characterized by severe hypoglycemia due to inappropriate insulin secretion. The genetic causes of CHI have been found in genes regulating insulin secretion from pancreatic ß-cells; recessive inactivating mutations in the ABCC8 and KCNJ11 genes represent the most common events. Despite the advances in understanding the molecular pathogenesis of CHI, specific genetic determinants in about 50 % of the CHI patients remain unknown, suggesting additional locus heterogeneity. In order to search for novel loci contributing to the pathogenesis of CHI, we combined a family-based association study, using the transmission disequilibrium test on 17 CHI patients lacking mutations in ABCC8/KCNJ11, with a whole-exome sequencing analysis performed on 10 probands. This strategy allowed the identification of the potential causative mutations in genes implicated in the regulation of insulin secretion such as transmembrane proteins (CACNA1A, KCNH6, KCNJ10, NOTCH2, RYR3, SCN8A, TRPV3, TRPC5), cytosolic (ACACB, CAMK2D, CDKAL1, GNAS, NOS2, PDE4C, PIK3R3) and mitochondrial enzymes (PC, SLC24A6), and in four genes (CSMD1, SLC37A3, SULF1, TLL1) suggested by TDT family-based association study. Moreover, the exome-sequencing approach resulted to be an efficient diagnostic tool for CHI, allowing the identification of mutations in three causative CHI genes (ABCC8, GLUD1, and HNF1A) in four out of 10 patients. Overall, the present study should be considered as a starting point to design further investigations: our results might indeed contribute to meta-analysis studies, aimed at the identification/confirmation of novel causative or modifier genes.

Genetic analysis of Italian patients with congenital hyperinsulinism of infancy.

BACKGROUND/AIMS: Congenital hyperinsulinism of infancy is a rare disease that needs prompt treatment to avoid brain damage. There are currently no data regarding the clinical and molecular features of Italian patients. METHODS: Thirty-three patients with HI and their parents were included. Consanguinity was reported in six patients. Half of patients were macrosomic at birth. None had raised 3-hydroxybutyrylcarnitine or hyperammonemia. Molecular analysis of ABCC8 and KCNJ11 genes was performed in all patients, and subjects with no mutation underwent analysis of HNF4A and GCK. GLUD1 and HADH genes were analyzed in a patient with leucine sensitivity. RESULTS: Mutations in the ABCC8 and KCNJ11 genes were found in 45% of the patients (6 novel). No mutations in HNF4A, GLUD1 and GCK genes were found. Recessive mode of inheritance was found in 21% of patients. A single heterozygous mutation was identified in 24% of probands. 72% of the patients were responsive to medical treatment, and 44% of the 17 patients with no identified mutation achieved spontaneous remission. Nine children, unresponsive to medical therapy, underwent pancreatectomy. CONCLUSION: This is the first report on hyperinsulinism of infancy in Italy, confirming the complexity of the clinical forms and the heterogeneity of the genetic causes of the disease.

Congenital hypothyroidism with eutopic thyroid gland: analysis of clinical and biochemical features at diagnosis and after re-evaluation.

CONTEXT: In recent years changes in screening strategies for congenital hypothyroidism (CH) led to an increased detection of mild forms of CH, associated with eutopic thyroid gland. OBJECTIVES: We aimed to determine the clinical evolution of CH with eutopic thyroid gland and to find out prognostic factors at diagnosis and follow-up. PATIENTS AND METHODS: We retrospectively analyzed a group of 84 children with CH and eutopic thyroid gland treated at our institution. They all underwent clinical re-evaluation after the age of 3, based on thyroid function testing after l-thyroxine therapy withdrawal, thyroid ultrasonography, and (123)I scintigraphy with perchlorate discharge test. Genetic analysis was performed in selected cases. RESULTS: At re-evaluation, 34.5% of patients showed permanent hypothyroidism and needed l-thyroxine reintroduction, 27.4% had persistent hyperthyrotropinemia (TSH 5-10 mU/L), and 38.1% had transient hypothyroidism. Major risk factors for permanent CH were prematurity, first-degree familial history of goiter/nodules, thyroid hypoplasia at diagnosis, and high l-thyroxine requirements at follow-up. Iodine organification defects were found in 29.7% of patients, 30% of whom harbored DUOX2 mutations. TSH receptor gene mutations were found in 8.7% of patients with persistent thyroid dysfunction and negative perchlorate discharge test. CONCLUSIONS: Only one-third of patients with CH and eutopic thyroid gland needed to continue l-thyroxine therapy after re-evaluation. A frequent finding was the persistence of mild hyperthyrotropinemia. The evolution of CH remains difficult to predict, although different clinical features might suggest different outcomes. Mutations in the genes commonly linked to mild forms of CH were documented in a minority of cases.

Tenofovir disoproxil fumarate and bone mineral density: a 60-month longitudinal study in a cohort of HIV-infected youths.

BACKGROUND: Decreased bone mineral density (BMD) has been associated with the use of tenofovir disoproxil fumarate (TDF) in HIV-infected adults. The data in HIV-infected children are conflicting. The aim of this study was to assess the safety of a TDF-containing antiretroviral (ARV) regimen on BMD in paediatric patients. We report the results of a longitudinal 60-month follow-up study. METHODS: A total of 21 vertically HIV-infected Caucasian youths (10 male and 11 female) on ARV treatment containing lamivudine, efavirenz and TDF were enrolled (age range 4.9-17.9 years at baseline). BMD was measured at the lumbar spine and in the whole skeleton by DXA. Bone-specific alkaline phosphatase (BAP) was measured as a bone formation marker and urinary N-telopeptide of type-I collagen (NTx) was measured as a bone resorption index. RESULTS: Baseline mean (±sd) BMD measurements of HIV-infected patients expressed as z-scores were -0.7 (±0.9) for lumbar spine and -0.13 (±1.0) for the whole skeleton. BMD measurements did not change significantly during the 60-month observation period. Both BAP and NTx concentrations were higher than a reference group of controls at baseline and remained unchanged throughout the study. CONCLUSIONS: Our data indicate that a TDF-containing regimen does not decrease the BMD of HIV-infected youths.

Pediatric HIV infection and bone health: an emerging challenge.

The available data indicate that HIV-infected children and adolescents have reduced bone mass compared to healthy peers. The increased survival due to the control of HIV infection by potent antiretroviral treatment, exposes patients to the achievement of a reduced peak bone mass and to an increased fracture risk during adult life. Reduced bone mass in HIV-infected children is the result of altered bone metabolism, showing significantly increased bone resorption rate. Both infection per se and the use of certain antiretroviral compounds seem to contribute to the altered metabolism. Preventative measures to improve bone health are thus necessary in all young patients that exhibit low bone mass measurements and altered bone metabolism.

Pseudohypoparathyroidism, an often delayed diagnosis: a case series.

Pseudohypoparathyroidism refers to a heterogeneous group of disorders characterized by parathyroid hormone (PTH) resistance. Pseudohypoparathyroidism is an uncommon sporadic or inherited genetic disorder subdivided into several distinct entities (type Ia, Ib, Ic, type II). We report cases of four children (aged 8 to 13 years) in the winter season 2007-'08. The present work highlights the variable mode of presentation of pseudohypoparathyroidism and the difficulty of an early diagnosis. We stress the importance of a complete biochemical investigation of the calcium-phosphate metabolism to recognize typical biochemical alterations associated with this condition (hypocalcaemia, hyperphosphataemia with increased phosphate tubular reabsorption and elevated PTH levels) in spite of a phenotypic aspect that often lacks the presence of all the peculiar clinical features of Albright hereditary osteodistrophy.

Differential effect of age, gender and puberty on bone formation rate assessed by measurement of bone-specific alkaline phosphatase in healthy Italian children and adolescents.

Bones undergo intensive modeling during growth, a process involving both formation and resorption processes. Bone formation can be accurately monitored by measurements of bone-specific alkaline phosphatase (BAP) in serum. The lack of appropriate reference values has hampered the use of BAP in pediatric subjects. The purposes of the present study were to verify the effect of age, gender, and puberty on BAP concentration in healthy children, and to generate reference curves. Morning blood samples were collected from 239 healthy children and adolescents (113 boys), aged 4.5-20.9 years. Anthropometric measurements and pubertal stage were recorded. Blood samples were also obtained from 37 healthy young adults (13 men), aged 21.5-30.2 years. BAP concentration varied significantly with age, showing a peak at age 10-12 years in girls and 12-14 years in boys. Prepubertal concentration of BAP was six- to sevenfold higher than in healthy adults. We observed significantly higher BAP values at the beginning of puberty (stage II) compared to prepubertal stage in both sexes. The effect of puberty was independent from age and gender. We demonstrated that BAP serum concentration varies with age in children and adolescents, and we provided equations to calculate reference values. Because BAP concentrations vary markedly according to the pubertal stage, the values of BAP obtained in single patients should be compared to reference considering not only age and sex, but also the stage of pubertal development.

Biallelic inactivation of the dual oxidase maturation factor 2 (DUOXA2) gene as a novel cause of congenital hypothyroidism.

CONTEXT: Dual oxidase 2 (DUOX2) is the catalytic core of the H(2)O(2) generator crucial for the iodination of thyroglobulin in thyroid hormone synthesis. DUOX2 deficiency produces congenital hypothyroidism (CH) in humans and mice. We recently cloned a novel gene, the product of which (dual oxidase maturation factor 2; DUOXA2) is required to express DUOX2 enzymatic activity. OBJECTIVE: Our objective was to identify DUOXA2 mutations as a novel cause of CH due to dyshormonogenesis. PATIENTS: Subjects included 11 CH patients with partial iodine organification defect but negative for other known genetic causes of partial iodine organification defect. RESULTS: One Chinese patient born to nonconsanguineous parents was homozygous for a nonsense mutation (p.Y246X), producing a truncated DUOXA2 protein lacking transmembrane helix 5 and the C-terminal cytoplasmic domain. The mutant protein was inactive in reconstituting DUOX2 in vitro. Pedigree analysis demonstrated recessive inheritance, because heterozygous carriers had normal thyroid function including negative results in neonatal TSH screening. One heterozygous carrier of Y246X was identified in unrelated Chinese controls (n = 92) but not in Caucasian or Japanese controls, indicating that homozygosity for Y246X could be a frequent cause of CH in Chinese. Functional studies suggest that the DUOXA2 paralog (DUOXA1) can partially compensate DUOXA2 deficiency, consistent with the proband having a milder CH phenotype than patients with biallelic DUOX2 nonsense mutations. CONCLUSIONS: We report the first mutation in DUOXA2, identified in a patient with CH and dyshormonogenic goiter. Results of our studies provide evidence for the critical role of DUOXA2 in thyroid hormonogenesis. Biallelic DUOXA2 mutations are a novel genetic event in permanent CH.

Normalization of fat accrual in lipoatrophic, HIV-infected children switched from stavudine to tenofovir and from protease inhibitor to efavirenz.

OBJECTIVE: An antiretroviral regimen based on lamivudine+stavudine+protease inhibitor impairs peripheral fat accrual in HIV-infected children and adolescents. We assess the effect on body composition parameters of replacing stavudine with tenofovir and protease inhibitor with efavirenz in paediatric patients. METHODS: A 96-week prospective study on 24 patients, (age range: 5.0-17.9 years) with stable undetectable HIV-1 loads, who were switched from stavudine to tenofovir and from protease inhibitor to efavirenz. Patient assessment included: body composition parameters measured by dual-energy X-ray absorptiometry (DXA), viral load and CD4+ T-count and percentage. As a control group for DXA data, we studied 143 healthy controls (HCs; age range: 4.9-20.0 years). RESULTS: Virological suppression and unchanged CD4+ T-cell count and percentage were maintained in all patients. At baseline, patients showed decreased total, arm and leg fat masses (P < 0.01) but a similar trunk fat mass to HCs. From baseline to week 96, patient fat mass increases were comparable to those for HCs (total fat: 1.3 vs 1.2 kg; fat in arms: 0.09 vs 0.08 kg; fat in legs: 0.5 vs 0.5 kg; trunk fat: 0.6 vs 0.6 kg). However, at week 96, total and leg fat mass in patients were still significantly lower than those in HCs (P < 0.02). At baseline and at week 96, lean mass in patients was similar to that expected in HCs. CONCLUSIONS: Replacing stavudine with tenofovir and protease inhibitor with efavirenz for 96 weeks in lipoatrophic paediatrics patients led to a restoration of physiological fat accrual. Lipoatrophy did not progress but was still present, indicating the need for additional strategies.

Alterations in circulating osteoimmune factors may be responsible for high bone resorption rate in HIV-infected children and adolescents.

OBJECTIVES: Bone metabolism derangements have been reported in HIV-infected children and adolescents. Nuclear factor kappa B ligand (RANKL) and osteoprotegerin potently stimulate and inhibit, respectively, osteoclast formation and activity. We investigated the possible role of RANKL and osteoprotegerin on bone metabolism alterations in paediatric patients. DESIGN: A prospective controlled longitudinal study. Measurements were obtained before and 6 months after switching antiretroviral regimen. METHODS: We studied 27 vertically HIV-infected children and adolescents (aged 4.9-17.3 years) on long-term HAART (70.1 +/- 1.5 months). All patients received lamivudine, stavudine and one protease inhibitor (PI). During follow-up, the PI was replaced with efavirenz and stavudine with tenofovir. We also enrolled 336 healthy children, aged 4.8-17.9 years. Concentrations of bone-specific alkaline phosphatase (BALP), N-terminal telopeptide of type I collagen (NTx), RANKL, and osteoprotegerin were measured at baseline and 6 months after switching. RESULTS: BALP serum concentrations and NTx urine levels of HIV-infected patients were significantly higher than those of healthy children both at baseline and after 6 months (P < 0.001). Baseline osteoprotegerin and RANKL concentrations of HIV-infected patients were significantly higher than in healthy children (P < 0.0001). Both concentrations decreased after 6 months, and RANKL levels were no longer different to controls. At baseline the RANKL/osteoprotegerin ratio was significantly higher (P = 0.02) in HIV-infected children (0.27 +/- 0.07) compared with healthy children (0.078 +/- 0.01). CONCLUSION: A marked alteration in the RANKL/osteoprotegerin system is present in patients receiving PI-based HAART. Short-term data indicate that replacing stavudine and PI with tenofovir and efavirenz restores the RANKL/osteoprotegerin equilibrium, and may thus lead to a reduction in the bone resorption rate.

Identification of two novel frameshift mutations in the KCNJ11 gene in two Italian patients affected by Congenital Hyperinsulinism of Infancy.

Congenital Hyperinsulinism of Infancy (CHI) is a genetically heterogeneous disorder characterized by profound hypoglycemia related to inappropriate insulin secretion. Two histopathologically and genetically distinct groups are recognized among patients with CHI due to ATP-sensitive potassium channel (KATP) defects: a diffuse type (Di-CHI), which involves the whole pancreas, and a focal form (Fo-CHI), which shows adenomatous islet-cell hyperplasia of a particular area within the normal pancreas. The beta-cell KATP channel consists of two essential subunits: Kir6.2 encoded by the KCNJ11 gene which is the pore-forming unit and belongs to the inwardly rectifying potassium channel family, and SUR1 (sulfonylurea receptor 1) encoded by the ABCC8 gene, which belongs to the ATP-binding cassette (ABC) transporter family. The KATP channel is an octameric complex of four Kir6.2 and four SUR1 subunits. More than one hundred mutations have been found in KATP channel genes ABCC8 and KCNJ11, but to date only twenty mutations have been identified in KCNJ11, most of them are missense mutations and only one is a single base deletion. The Fo-CHI has been demonstrated to arise in individuals who have a germline mutation in the paternal allele of ABCC8 or KCNJ11 in addition to a somatic loss of the maternally derived chromosome region 11p15 in adenomatous pancreatic beta-cells, while Di-CHI predominantly arises from the autosomal recessive inheritance of KATP channel gene mutations. Here we describe the molecular findings in nine children who presented, in the neonatal period, with signs and symptoms of hypoglycemia and diagnosed affected by CHI according to international diagnostic criteria. Direct sequencing of the complete coding exon and promoter region of KCNJ11 gene showed, in two Italian patients, two new heterozygous mutations which result in the appearance of premature translation termination codons resulting in the premature end of Kir6.2. Interestingly most of the CHI mutations detected in other population studies are situated in the ABCC8 gene.

Persistent mild hypothyroidism associated with novel sequence variants of the DUOX2 gene in two siblings.

One of the steps in thyroid hormone biosynthesis is the generation of hydrogen peroxide by dual oxidases (DUOX). Only one study reported mutations in DUOX2 gene in congenital hypothyroidism (CH) associated with total iodide organification defect (TIOD) in homozygosity or with partial iodide organification defect (PIOD) in heterozygous patients. We report genetic and phenotypic characterization of a family affected with isolated CH. The proband was positive at neonatal TSH screening. High serum TSH with low FT4 confirmed the diagnosis. At 4 years, TSH was high after L-T(4) withdrawal and (123)I scintigraphy with perchlorate discharge test revealed a PIOD. His brother was negative at TSH screening, but perinatal iodine overload was documented by urinary test. Serum TSH was elevated at postnatal day 11 and progressively increased together with a decline in urinary iodine. Reevaluation at 4 years confirmed a persistent hyperthyrotropinemia associated with PIOD. Both siblings resulted compound heterozygotes for two novel DUOX2 variants, a nonsense mutation (c.2524C>T, p.Arg842X) and a missense substitution (c.1126C>T, p.Arg376Trp), undetected in 140 control alleles. The parents had normal thyroid function and were heterozygous carriers of mutant alleles. In conclusion, we report two novel sequence variants in DUOX2 gene that are associated with persistent mild hypothyroidism and PIOD in two siblings. Different neonatal iodine supply apparently acted as disease modifier, justifying the discrepant results at TSH screening in the two siblings with same DUOX2 genotype and suggesting that mild dyshormonogenic defects may remain undisclosed in areas characterized by elevated iodine intake.

Autosomal dominant hypocalcemia in monozygotic twins caused by a de novo germline mutation near the amino-terminus of the human calcium receptor.

UNLABELLED: To define the molecular pathogenesis of severe postnatal hypocalcemia in monozygotic twin sisters, we sequenced their CaR gene and identified a missense mutation, K29E. Expression of the mutant receptor in vitro showed a marked increase in Ca2+ sensitivity explaining the observed phenotype. Additional mutagenesis studies lead us to speculate concerning a novel mechanism whereby the K29E mutation may lead to receptor activation. INTRODUCTION: Activating mutations of the Ca(2+)-sensing receptor (CaR) gene have been identified in subjects with autosomal dominant hypocalcemia. Study of such mutations has provided insight into the mechanism of activation of the CaR. MATERIALS AND METHODS: We performed biochemical and molecular genetic studies on monozygotic twin sisters who presented with early postnatal hypocalcemia and on their unaffected sister and parents. Functional characterization of mutant CaRs transfected in HEK-293 cells included immunoblots to monitor protein expression and Ca2+ stimulation of phosphoinositide hydrolysis to measure Ca2+ sensitivity. RESULTS: We identified a K29E missense mutation in the twin sisters but not in their parents or unaffected sister. The K29E mutant CaR showed a marked increase in Ca2+ sensitivity, including when it was co-transfected with wildtype CaR cDNA, consistent with a dominant effect. Substitution of K29 by aspartate equivalently increased CaR sensitivity, whereas conservative substitution by arginine did not. CONCLUSIONS: Severe postnatal hypocalcemia in the twin sisters was caused by a de novo germline activating mutation. In a model of the Venus flytrap-like domain of the extracellular amino-terminus of the CaR, K29 is located close to a peptide loop, "loop 2," that forms part of the dimer interface and is the site of 10 of the previously reported naturally occurring activating CaR mutations. We speculate that K29E increases Ca2+ sensitivity of the CaR by disrupting a salt bridge between K29 and an acidic residue in loop 2 and thereby changes the normal structure of loop 2 that maintains the CaR in its inactive conformation.

Longitudinal changes of bone mineral density and metabolism in antiretroviral-treated human immunodeficiency virus-infected children.

Highly active antiretroviral therapy (HAART) may be a contributory factor for a decreased bone mass and altered bone metabolism in HIV-infected children. However, the evolution of bone mineral density (BMD) and bone metabolism during HAART has not been studied yet. In the current longitudinal study we monitored the changes of BMD and bone metabolism over a period of 12 months. Thirty-two HIV-infected children (15 girls and 17 boys), aged from 6.3 to 17.7 yr, with a long duration of HAART exposure (40.0 months at baseline) were enrolled in the study. As a control group, 381 healthy volunteers of comparable age were assessed. BMD was measured at the lumbar spine and whole skeleton by dual-energy x-ray absorptiometry. Bone-specific alkaline phosphatase (BALP, as bone formation index) and N-terminal telopeptide of type I collagen (as bone resorption index) were measured in serum and urine, respectively. BMD values at baseline were significantly lower at all skeletal sites than those of control subjects. The annual increment of spine BMD was comparable to normal, whereas that of the whole skeleton was significantly lower (P < 0.04). BALP and N-terminal telopeptide of type I collagen concentrations were significantly higher compared with controls at baseline and at follow-up. BALP annual changes of HIV patients were significantly different from normal. Our data confirm the presence of low BMD and bone metabolism derangement in HIV-infected children treated with HAART. The role of possible therapeutic approach to restore bone mass and metabolism should be assessed in pediatrics.