Abdullah Bereket

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.

Consensus Development for the Supplementation of Vitamin D in Childhood and Adolescence

aMeyer Children Hospital, Haifa, Israel; bMarmara University, Istanbul, Turkey; cUniversity of North Carolina, Chapel Hill, N.C., USA; dVrije Universiteit, Amsterdam, The Netherlands; eAcademic Hospital V.V.B., Brussels, Belgium; fJohns Hopkins University, Baltimore, Md., USA; gBirmingham Children’s Hospital, Birmingham, UK; hUniversitatskinderklinik, Cologne, Germany; iDana Children’s Hospital, Tel Aviv, Israel; jKaplan Hospital Rehovot, Israel

Ten Novel Mutations in the NR5A1 Gene Cause Disordered Sex Development in 46,XY and Ovarian Insufficiency in 46,XX Individuals

CONTEXT Steroidogenic factor-1 (SF-1/NR5A1) is a nuclear receptor that regulates adrenal and reproductive development and function. NR5A1 mutations have been detected in 46,XY individuals with disorders of sexual development (DSD) but apparently normal adrenal function and in 46,XX women with normal sexual development yet primary ovarian insufficiency (POI). OBJECTIVE A group of 100 46,XY DSD and two POI was studied for NR5A1 mutations and their impact. DESIGN Clinical, biochemical, histological, genetic, and functional characteristics of the patients with NR5A1 mutations are reported. SETTING Patients were referred from different centers in Spain, Switzerland, and Turkey. Histological and genetic studies were performed in Barcelona, Spain. In vitro studies were performed in Bern, Switzerland. PATIENTS A total of 65 Spanish and 35 Turkish patients with 46,XY DSD and two Swiss 46,XX patients with POI were investigated. MAIN OUTCOME Ten novel heterozygote NR5A1 mutations were detected and characterized (five missense, one nonsense, three frameshift mutations, and one duplication). RESULTS The novel NR5A1 mutations were tested in vitro by promoter transactivation assays showing grossly reduced activity for mutations in the DNA binding domain and variably reduced activity for other mutations. Dominant negative effect of the mutations was excluded. We found high variability and thus no apparent genotype-structure-function-phenotype correlation. Histological studies of testes revealed vacuolization of Leydig cells due to fat accumulation. CONCLUSIONS SF-1/NR5A1 mutations are frequently found in 46,XY DSD individuals (9%) and manifest with a broad phenotype. Testes histology is characteristic for fat accumulation and degeneration over time, similar to findings observed in patients with lipoid congenital adrenal hyperplasia (due to StAR mutations). Genotype-structure-function-phenotype correlation remains elusive.

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.

Hypothalamic obesity in children

Hypothalamic obesity is an intractable form of obesity syndrome that was initially described in patients with hypothalamic tumours and surgical damage. However, this definition is now expanded to include obesity developing after a variety of insults, including intracranial infections, infiltrations, trauma, vascular problems and hydrocephalus, in addition to acquired or congenital functional defects in central energy homeostasis in children with the so‐called common obesity. The pathogenetic mechanisms underlying hypothalamic obesity are complex and multifactorial. Weight gain results from damage to the ventromedial hypothalamus, which leads, variously, to hyperphagia, a low‐resting metabolic rate; autonomic imbalance; growth hormone‐, gonadotropins and thyroid‐stimulating hormone deficiency; hypomobility; and insomnia. Hypothalamic obesity did not receive enough attention, as evidenced by rarity of studies in this group of patients. A satellite symposium was held during the European Congress of Obesity in May 2011, in Istanbul, Turkey, to discuss recent developments and concepts regarding pathophysiology and management of hypothalamic obesity in children. An international group of leading researchers presented certain aspects of the problem. This paper summarizes the highlights of this symposium. Understanding the central role of the hypothalamus in the regulation of feeding and energy metabolism will help us gain insights into the pathogenesis and management of common obesity.

Insulin treatment normalizes reduced free insulin-like growth factor-I concentrations in diabetic children.

OBJECTIVE We have recently demonstrated multiple aberrations in the GH–IGF axis in the sera of children with untreated insulin‐dependent diabetes mellitus (IDDM) which were restored after insulin replacement. However, the net result of these alterations in the IGF system on the concentrations of free/biologically available IGF‐I in the serum have not been examined directly in diabetic children. In the present study, the effect of diabetes and subsequent insulin replacement on the circulating free IGF‐I concentrations are assessed.

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.

Vitamin D deficiency and prevention: Turkish experience

A nationwide ‘vitamin D prophylaxis augmentation programme’ initiated in 2005 in Turkey reduced the prevalence of rickets from 6% in 1998 to 0.1% in 2008 in children under 3 years of age. The programme included free distribution of vitamin D drops to all newborns and infants (0–12 months) visiting primary health stations throughout the country. Free disposal of vitamin D to infants is an effective strategy for preventing vitamin D‐deficient rickets.