Serap Turan

Hypogonadotropic Hypogonadism due to a Novel Missense Mutation in the First Extracellular Loop of the Neurokinin B Receptor

CONTEXT The neurokinin B (NKB) receptor, encoded by TACR3, is widely expressed within the central nervous system, including hypothalamic nuclei involved in regulating GnRH release. We have recently reported two mutations in transmembrane segments of the receptor and a missense mutation in NKB in patients with normosmic isolated hypogonadotropic hypogonadism (nIHH). PATIENTS AND METHODS We sequenced the TACR3 gene in a family in which three siblings had nIHH. The novel mutant receptor thus identified was studied in a heterologous expression system using calcium flux as the functional readout. RESULTS All affected siblings were homozygous for the His148Leu mutation, in the first extracellular loop of the NKB receptor. The His148Leu mutant receptor exhibited profoundly impaired signaling in response to NKB (EC(50) = 3 +/- 0.1 nm and >5 microm for wild-type and His148Leu, respectively). The location of the mutation in an extracellular part of the receptor led us also to test whether senktide, a synthetic NKB analog, may retain ability to stimulate the mutant receptor. However, the signaling activity of the His148Leu receptor in response to senktide was also severely impaired (EC(50) = 1 +/- 1 nm for wild-type and no significant response of His148Leu to 10 microm). CONCLUSIONS Homozygosity for the TACR3 His148Leu mutation leads to failure of sexual maturation in humans, whereas signaling by the mutant receptor in vitro in response to either NKB or senktide is severely impaired. These observations further strengthen the link between NKB, the NKB receptor, and regulation of human reproductive function.

Serum IGF-I and IGFBP-3 levels of Turkish children during childhood and adolescence: establishment of reference ranges with emphasis on puberty.

Aims/Methods: We established age- and sex-related reference ranges for serum insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) levels in 807 healthy Turkish children (428 boys, 379 girls), and constructed a model for calculation of standard deviation scores of IGF-I and IGFBP-3 according to age, sex and pubertal stage. Results: Serum IGF-I and IGFBP-3 concentrations tended to be higher in girls compared to boys of the same ages, but the differences were statistically significant only in pubertal ages (9–14 years) for IGF-I and only in prepubertal ages for IGFBP-3 (6–8 years) (p < 0.05). Peak IGF-I concentrations were observed earlier in girls than boys (14 vs. 15 years, Tanner stage IV vs. V) starting to decline thereafter. IGFBP-3 levels peaked at age 13 and at Tanner stage IV in both sexes with a subsequent fall. Serum levels of IGF-I and IGFBP-3 increased steadily with age in the prepubertal stage followed by a rapid increase in IGF-I in the early pubertal stages. A relatively steeper increase in IGF-I but not in IGFBP-3 levels was observed at age 10–11 years in girls and at 12–13 years in boys which preceded the reported age of pubertal growth spurt. At late pubertal stages, both IGF-I and IGFBP-3 either did not change or decreased by increasing age. Interrelationships between growth factors and anthropometric measurements have been described, and the physiologic consequences of these have been discussed in detail. Conclusions: Differences in the pattern of IGF-I and IGFBP-3 in the present paper and those reported in other studies emphasize the importance of locally established reference ranges. Establishment of this reference data and a standard deviation score prediction model based on age, sex and puberty will enhance the diagnostic power and utility of IGF-I and IGFBP-3 in evaluating growth disorders in our population.

Serum alkaline phosphatase levels in healthy children and evaluation of alkaline phosphatase z-scores in different types of rickets.

Objective: Serum alkaline phosphatase (ALP) levels show great variation with age and sex in children and adolescents. Additionally, different buffers used even in the same method cause variable results. This detail is not usually taken into account in the evaluation. We aimed to study pediatric age- and sex-specific reference ranges for ALP by colorimetric assay using p-nitrophenyl phosphate as substrate and diethanolamine as buffer and also to compare the ALP levels in patients with different types of rickets. Methods: 1741 healthy children and adolescents (904 girls) were included in the study for normative data. 77 different ALP measurements from 38 nutritional rickets (NR), 7 vitamin D-dependent rickets (VDDR) and 8 hypophosphatemic rickets (HR) patients were included. Results: Reference values for ALP were constructed. ALP levels demonstrated a tetraphasic course with two peaks at infancy and puberty. There was no difference in ALP levels between boys and girls until puberty. However, higher ALP levels were noted at 10-11 years in girls (p=0.02) and at 12-13, 14-15, 16-17 years in boys (p<0.001). ALP levels start to decline after age 12 and 14 in girls and boys, respectively. Serum ALP levels were highest in the VDDR group and lowest in the HR group (median z-score values in HR, VDDR and NR were 3.6, 10.4 and 6.5, respectively; p<0.001). Similarly, plasma parathormone(PTH) levels ranged from highest to lowest in the VDDR, NR and HR groups (median values: 525, 237 and 98 pg/mL, respectively; p<0.001). Conclusions: This normative data will provide a basis for better evaluation of ALP levels determined by the described method. Furthermore, use of z-scores gives a more precise assessment of changes in ALP levels in rickets and other bone disorders. Conflict of interest:None declared.

Significance of acanthosis nigricans in childhood obesity

Aim:  Acanthosis nigricans (AN) is among the most common dermatologic manifestations of obesity and hyperinsulinism. In this study, we aimed to find the clinical and laboratory differences in obese children with AN and without AN (non‐AN).

Rare Causes of Primary Adrenal Insufficiency: Genetic and Clinical Characterization of a Large Nationwide Cohort

Context: Primary adrenal insufficiency (PAI) is a life-threatening condition that is often due to monogenic causes in children. Although congenital adrenal hyperplasia occurs commonly, several other important molecular causes have been reported, often with overlapping clinical and biochemical features. The relative prevalence of these conditions is not known, but making a specific diagnosis can have important implications for management. Objective: The objective of the study was to investigate the clinical and molecular genetic characteristics of a nationwide cohort of children with PAI of unknown etiology. Design: A structured questionnaire was used to evaluate clinical, biochemical, and imaging data. Genetic analysis was performed using Haloplex capture and next-generation sequencing. Patients with congenital adrenal hyperplasia, adrenoleukodystrophy, autoimmune adrenal insufficiency, or obvious syndromic PAI were excluded. Setting: The study was conducted in 19 tertiary pediatric endocrinology clinics. Patients: Ninety-five children (48 females, aged 0–18 y, eight familial) with PAI of unknown etiology participated in the study. Results: A genetic diagnosis was obtained in 77 patients (81%). The range of etiologies was as follows: MC2R (n = 25), NR0B1 (n = 12), STAR (n = 11), CYP11A1 (n = 9), MRAP (n = 9), NNT (n = 7), ABCD1 (n = 2), NR5A1 (n = 1), and AAAS (n = 1). Recurrent mutations occurred in several genes, such as c.560delT in MC2R, p.R451W in CYP11A1, and c.IVS3ds+1delG in MRAP. Several important clinical and molecular insights emerged. Conclusion: This is the largest nationwide study of the molecular genetics of childhood PAI undertaken. Achieving a molecular diagnosis in more than 80% of children has important translational impact for counseling families, presymptomatic diagnosis, personalized treatment (eg, mineralocorticoid replacement), predicting comorbidities (eg, neurological, puberty/fertility), and targeting clinical genetic testing in the future.

Identification of a novel dentin matrix protein-1 (DMP-1) mutation and dental anomalies in a kindred with autosomal recessive hypophosphatemia

An autosomal recessive form of hypophosphatemia (ARHP) was recently shown to be caused by homozygous mutations in DMP1, the gene encoding dentin matrix protein-1 (DMP-1), a non-collagenous bone matrix protein with an important role in the development and mineralization of bone and teeth. Here, we describe a previously not reported consanguineous ARHP kindred in which the three affected individuals carry a novel homozygous DMP-1 mutation. The index case presented at the age of 3 years with bowing of his legs and showed hypophosphatemia due to insufficient renal phosphate retention. Serum alkaline phosphatase activity was elevated, with initially normal PTH. FGF23 was inappropriately normal at an older age while being treated with oral phosphate and 1,25(OH)(2)D. Similar clinical and biochemical findings, except for elevated FGF23 levels, were present in his 16-month-old brother and his 12.5-year-old female cousin; the parents of the three affected children are first-degree cousins. Nucleotide sequence analysis was performed on PCR-amplified exons encoding DMP-1 and flanking intronic regions. A novel homozygous frame-shift mutation (c.485Tdel; p.Glu163ArgfsX53) in exon 6 resulting in a premature stop codon was identified in all effected individuals. The parents and available unaffected siblings were heterozygous for c.485Tdel. Tooth growth and shape were normal for the index case, his affected brother and cousin, but their permanent and deciduous teeth displayed enlarged pulp chambers. The identified genetic mutation underscores the importance of DMP-1 mutations in the pathogenesis of ARHP. Furthermore, DMP-1 mutations appear to contribute, through yet unknown mechanisms, to tooth development.

Puberty and Influencing Factors in Schoolgirls Living in Istanbul: End of the Secular Trend?

OBJECTIVE: To (1) establish the median ages at menarche and pubertal stages and investigate influential factors and (2) assess the secular trend in reaching puberty in a transitional society. MATERIALS AND METHODS: A probit method was used to calculate the median age at menarche and pubertal stages from a cross-sectional study of 4868 healthy schoolgirls (aged 6–18 years) in Istanbul, Turkey. The findings were compared with those from a similar study performed 4 decades earlier. Logistic regression was used to analyze the associations between the odds of attaining puberty stages and putatively influential factors. Simple statistical models were used to test the effects of BMI and consumption of certain foods on the onset of menarche. RESULTS: The median age at menarche is 12.74 years. The median ages at breast stages 2 through 5 are 9.65, 10.10, 11.75, and 14.17 years, respectively, and at pubic-hair stages 2 through 5 are 10.09, 11.19, 12.33, and 14.68 years, respectively. Girls from upper socioeconomic classes are more likely to reach menarche and B4 and B5 stages. Higher BMI seems to be a promoting factor for attaining menarche. Intrauterine growth and gestational age had no effect. The average age at menarche was not associated with the consumption of milk, eggs, chicken, or fish. CONCLUSIONS: The secular trend in puberty is probably about to end in Turkey. Although the median ages at the breast stages show a decreasing trend, the median age at menarche is approximately the same as it was 4 decades ago. Socioeconomic status and BMI are important, and related, factors that affect the age at menarche and pubertal stages.

Effect of zinc supplementation on growth hormone secretion, IGF-I, IGFBP-3, somatomedin generation, alkaline phosphatase, osteocalcin and growth in prepubertal children with idiopathic short stature

Controversy exists about the effect of zinc on growth and the GH-IGF system. Zinc supplementation has been shown to stimulate linear growth in zinc-deficient children. However the mechanism of this effect has not been well characterized. Furthermore, the effect of zinc supplementation on non-zinc-deficient short children is unknown. We investigated the effect of zinc supplementation on endogenous GH secretion, serum IGF-I and IGFBP-3 concentrations, IGF-I and IGFBP-3 generation in response to exogenous GH, bone formation markers, and linear growth of non-zinc-deficient children with idiopathic short stature. We analyzed prospectively serum zinc, IGF-I, IGFBP-3, alkaline phosphatase, osteocalcin, and GH response to clonidine test, and performed a somatomedin generation test before and 6 weeks after zinc supplementation in 22 (16 M, 6 F) prepubertal children with idiopathic short stature. Serum IGF-I increased from 67.4+/-70.6 to 98.2+/-77.3 ng/ml (p <0.001), IGFBP-3 from 2326+/-770 to 2758+/-826 ng/ml (p <0.001), alkaline phosphatase from 525+/-136 to 666+/-197 U/l (p <0.0001), and osteocalcin from 16.8+/-10.6 to 25.8+/-12.8 ng/ml (p <0.05) after zinc supplementation despite there being no difference in GH response to clonidine after zinc supplementation (peak GH 11.6+/-6.9 vs 13.4+/-7.8 ng/ml, GH area under the curve during clonidine test 689+/-395 vs 761+/-468, NS). Percent change in IGF-I and IGFBP-3 during the somatomedin generation test was not significantly affected by zinc supplementation (118% vs 136% and 57% vs 44%, respectively). There was no significant correlation between percentage increase in zinc levels and percentage increase in parameters tested. Height SDS or weight SDS did not improve significantly in 17 patients who continued on zinc supplementation for at least 6 months (6-12 months) (-2.59 vs -2.53 SDS and -1.80 vs -1.67 SDS, respectively). Zinc supplementation increased basal IGF-I, IGFBP-3, alkaline phosphatase and osteocalcin without changing GH response to clonidine. Zinc supplementation did not affect sensitivity to exogenous GH as tested by IGF-I and IGFBP-3 generation test. These results suggest a direct stimulatory effect of zinc on serum IGF-IGFBP-3, alkaline phosphatase and osteocalcin. Despite improvements in the above parameters, zinc supplementation to children with idiopathic short stature with normal serum zinc levels did not significantly change height or weight SDS during 6-12 months follow-up.

GNAS spectrum of disorders

The GNAS complex locus encodes the alpha-subunit of the stimulatory G protein (Gsα), a ubiquitous signaling protein mediating the actions of many hormones, neurotransmitters, and paracrine/autocrine factors via generation of the second messenger cAMP. GNAS gives rise to other gene products, most of which exhibit exclusively monoallelic expression. In contrast, Gsα is expressed biallelically in most tissues; however, paternal Gsα expression is silenced in a small number of tissues through as-yet-poorly understood mechanisms that involve differential methylation within GNAS. Gsα-coding GNAS mutations that lead to diminished Gsα expression and/or function result in Albright’s hereditary osteodystrophy (AHO) with or without hormone resistance, i.e., pseudohypoparathyroidism type-Ia/Ic and pseudo-pseudohypoparathyroidism, respectively. Microdeletions that alter GNAS methylation and, thereby, diminish Gsα expression in tissues in which the paternal Gsα allele is normally silenced also cause hormone resistance, which occurs typically in the absence of AHO, a disorder termed pseudohypoparathyroidism type-Ib. Mutations of GNAS that cause constitutive Gsα signaling are found in patients with McCune-Albright syndrome, fibrous dysplasia of bone, and different endocrine and non-endocrine tumors. Clinical features of these diseases depend significantly on the parental allelic origin of the GNAS mutation, reflecting the tissue-specific paternal Gsα silencing. In this article, we review the pathogenesis and the phenotypes of these human diseases.

Long‐term clinical outcome and carrier phenotype in autosomal recessive hypophosphatemia caused by a novel DMP1 mutation

Homozygous inactivating mutations in DMP1 (dentin matrix protein 1), the gene encoding a noncollagenous bone matrix protein expressed in osteoblasts and osteocytes, cause autosomal recessive hypophosphatemia (ARHP). Herein we describe a family with ARHP owing to a novel homozygous DMP1 mutation and provide a detailed description of the associated skeletal dysplasia and carrier phenotype. The two adult patients with ARHP, a 78‐year‐old man and his 66‐year‐old sister, have suffered from bone pain and lower extremity varus deformities since early childhood. With increasing age, both patients developed severe joint pain, contractures, and complete immobilization of the spine. Radiographs showed short and deformed long bones, significant cranial hyperostosis, enthesopathies, and calcifications of the paraspinal ligaments. Biochemistries were consistent with hypophosphatemia owing to renal phosphate wasting; markers of bone turnover and serum fibroblast growth factor 23 (FGF‐23) levels were increased significantly. Nucleotide sequence analysis of DMP1 revealed a novel homozygous mutation at the splice acceptor junction of exon 6 (IVS5‐1G > A). Two heterozygous carriers of the mutation also showed mild hypophosphatemia, and bone biopsy in one of these individuals showed focal areas of osteomalacia. In bone, DMP1 expression was absent in the homozygote but normal in the heterozygote, whereas FGF‐23 expression was increased in both subjects but higher in the ARHP patient. The clinical and laboratory observations in this family confirm that DMP1 has an important role in normal skeletal development and mineral homeostasis. The skeletal phenotype in ARHP may be significantly more severe than in other forms of hypophosphatemic rickets.