Identification of SLC20A1 and SLC15A4 among other genes as potential risk factors for combined pituitary hormone deficiency.

PURPOSE: Combined pituitary hormone deficiency (CPHD) is characterized by a malformed or underdeveloped pituitary gland resulting in an impaired pituitary hormone secretion. Several transcription factors have been described in its etiology, but defects in known genes account for only a small proportion of cases. METHODS: To identify novel genetic causes for congenital hypopituitarism, we performed exome-sequencing studies on 10 patients with CPHD and their unaffected parents. Two candidate genes were sequenced in further 200 patients. Genotype data of known hypopituitary genes are reviewed. RESULTS: We discovered 51 likely damaging variants in 38 genes; 12 of the 51 variants represent de novo events (24%); 11 of the 38 genes (29%) were present in the E12.5/E14.5 pituitary transcriptome. Targeted sequencing of two candidate genes, SLC20A1 and SLC15A4, of the solute carrier membrane transport protein family in 200 additional patients demonstrated two further variants predicted as damaging. We also found combinations of de novo (SLC20A1/SLC15A4) and transmitted variants (GLI2/LHX3) in the same individuals, leading to the full-blown CPHD phenotype. CONCLUSION: These data expand the pituitary target genes repertoire for diagnostics and further functional studies. Exome sequencing has identified a combination of rare variants in different genes that might explain incomplete penetrance in CPHD.

Combined pituitary hormone deficiency due to gross deletions in the POU1F1 (PIT-1) and PROP1 genes.

Pituitary development depends on a complex cascade of interacting transcription factors and signaling molecules. Lesions in this cascade lead to isolated or combined pituitary hormone deficiency (CPHD). The aim of this study was to identify copy number variants (CNVs) in genes known to cause CPHD and to determine their structure. We analyzed 70 CPHD patients from 64 families. Deletions were found in three Turkish families and one family from northern Iraq. In one family we identified a 4.96 kb deletion that comprises the first two exons of POU1F1. In three families a homozygous 15.9 kb deletion including complete PROP1 was discovered. Breakpoints map within highly homologous AluY sequences. Haplotype analysis revealed a shared haplotype of 350 kb among PROP1 deletion carriers. For the first time we were able to assign the boundaries of a previously reported PROP1 deletion. This gross deletion shows strong evidence to originate from a common ancestor in patients with Kurdish descent. No CNVs within LHX3, LHX4, HESX1, GH1 and GHRHR were found. Our data prove multiplex ligation-dependent probe amplification to be a valuable tool for the detection of CNVs as cause of pituitary insufficiencies and should be considered as an analytical method particularly in Kurdish patients.

Clinical and biochemical consequences of an intragenic growth hormone receptor (GHR) deletion in a large Chinese pedigree.

OBJECTIVE: Growth hormone insensitivity (GHI) may be caused by failure of GH receptor function. Some patients bearing specific GHR mutations differ from classical GHI individuals by extremely elevated GH-binding protein (GHBP) serum concentrations. We investigated clinical, genetic and biochemical characteristics of a severely growth-retarded Chinese boy with classical Laron syndrome manifestations. PATIENTS AND MEASUREMENTS: DNA and mRNA from blood cells of the patient and 11 family members were investigated for GHR mutations. Basal GH, GHBP, IGF-1 and IGFBP-3 concentrations were determined in serum samples. The impact of the aberrant mRNA on GHR protein expression and secretion was analysed in vitro by transfection studies in HEK293 cells. RESULTS: The proband and seven relatives had excessively elevated GHBP serum concentration. Basal GH in these individuals was significantly greater compared with family members with normal GHBP. The GHBP increase originated from a novel GHR intragenic deletion comprising parts of exon and intron 8 that caused exon 8 skipping from the GHR mRNA transcript. Transfection studies revealed that the predicted loss of plasma membrane anchorage results in direct secretion of the mutant GHR. CONCLUSIONS: The partial GHR deletion causes excessively elevated GHBP serum concentrations regardless of the state of zygosity of the mutation. The increase in GHBP is associated with significantly elevated basal GH levels. Clinically, only homozygous carriers exhibit classical GHI manifestations. The truncated GHR protein resulting from exon 8 skipping is directly secreted out of the cell.

The interaction of glucocorticoids and progesterone distinctively affects epithelial sodium transport.

PURPOSE: Glucocorticoids and progesterone exert stimulatory effects on epithelial Na(+) transport, including increased mRNA expression of the participating ion transporters (epithelial Na(+) channels [ENaC] and Na,K-ATPases) and their electrophysiological activity. Fetuses threatened by preterm labor may receive high doses of glucocorticoids to stimulate lung maturation and are naturally exposed to high levels of female sex steroids. However, it is still unknown how the combination of both hormones influences the epithelial Na(+) transport, which is crucial for alveolar fluid clearance. METHODS: Fetal distal lung epithelial cells were incubated in media supplemented with dexamethasone and progesterone. Real-time qPCR and Ussing chamber analysis were used to determine the effects on ENaC mRNA expression and channel activity. In addition, the specific progesterone receptor antagonist (PF-02367982) and the glucocorticoid receptor antagonist mifepristone were used to identify the involved hormone receptors. RESULTS: Both dexamethasone and progesterone increased ENaC subunit expression and channel activity. However, the combination of dexamethasone and progesterone reduced the α- and γ-ENaC subunit expression compared to the effect of dexamethasone alone. Furthermore, higher dexamethasone concentrations in combination with progesterone also significantly reduced Na(+) transport in Ussing chamber measurements. Hormone receptor antagonists showed that inhibition of the progesterone receptor increased the mRNA expression of α- and γ-ENaC, whereas mifepristone decreased mRNA expression of all ENaC subunits. CONCLUSION: Glucocorticoids and progesterone individually increase ENaC mRNA expression; however, the combination of both hormones decreases the stimulatory effects of dexamethasone on Na(+) transport and ENaC mRNA expression.

Estrogen modulates plasminogen promoter activity.

Postmenopausal women treated with estrogen hormone replacement therapy and female patients with hypoplasminogenemia receiving oral contraceptives show increasing plasminogen (PLG) concentrations. The elevated PLG levels are in contrast to the estrogen dependent decline of lipoptrotein(a) [Lp(a)], whose main protein component apolipoprotein(a) [APO(a)] is highly homologous to PLG in protein and gene structure and is also located in its immediate vicinity on chromosome 6q26. The intergenic region between both genes comprises several transcription-regulatory regions with enhancer sequences that increase the basal activity of the PLG core promoter. Using luciferase reporter assays we demonstrate that the minimal PLG promoter is insensitive to estrogen. However, an estrogen response element located 11.5 kb upstream of the PLG transcription start site is able to convey a dramatic estrogen-dependent elevation of PLG-minimal promoter driven reporter gene expression. In contrast, the activating effect of two additional enhancer elements, among them an DNase I hypersensitivity region that has been shown to regulate the APO(a) minimal promoter activity, is abrogated by estrogen. Thus, the identified estrogen-responsive elements provide a gene and tissue specific framework by which PLG expression is regulated and whose activity is orchestrated by yet unknown accessory factors.

Genetic analyses of bone morphogenetic protein 2, 4 and 7 in congenital combined pituitary hormone deficiency.

BACKGROUND: The complex process of development of the pituitary gland is regulated by a number of signalling molecules and transcription factors. Mutations in these factors have been identified in rare cases of congenital hypopituitarism but for most subjects with combined pituitary hormone deficiency (CPHD) genetic causes are unknown. Bone morphogenetic proteins (BMPs) affect induction and growth of the pituitary primordium and thus represent plausible candidates for mutational screening of patients with CPHD. METHODS: We sequenced BMP2, 4 and 7 in 19 subjects with CPHD. For validation purposes, novel genetic variants were genotyped in 1046 healthy subjects. Additionally, potential functional relevance for most promising variants has been assessed by phylogenetic analyses and prediction of effects on protein structure. RESULTS: Sequencing revealed two novel variants and confirmed 30 previously known polymorphisms and mutations in BMP2, 4 and 7. Although phylogenetic analyses indicated that these variants map within strongly conserved gene regions, there was no direct support for their impact on protein structure when applying predictive bioinformatics tools. CONCLUSIONS: A mutation in the BMP4 coding region resulting in an amino acid exchange (p.Arg300Pro) appeared most interesting among the identified variants. Further functional analyses are required to ultimately map the relevance of these novel variants in CPHD.

From GHRH to IGF-1 and downstream: clinical phenotypes and biological mechanisms.

Genetic defects have been observed at almost all levels of the GHRH-IGF-1 axis. The first observations of GH-1 gene deletions date some 30 years ago. Whereas mutations in the GH-1 and GHRHR genes account for the majority of mutations detectable in patients with Isolated Growth Hormone Deficiency (IGHD) resulting in postnatal growth failure, the overall detection of genetic defects in these patients remains low with app. 10-15%. Similarly, at the lower end of the GHRH-IGF-1 axis the frequency of defects within the IGF-1 and IGF-1 receptor (IGF1R) genes might hardly approach 10% of all cases with intrauterine and postnatal growth retardation. In this article we examine the pathomechanisms involved in the genetic defects at both ends of the GHRH-IGF-1 axis and describe the clinical and biochemical phenotypes involved. Although it seems tempting to increase the detection rate by limiting genetic investigations to patients with phenotypic characteristics described, at present it seems more appropriate to follow a permissive approach for such investigations as we are probably have not envisioned the full spectrum of phenotypic variability.

A Comprehensive Cohort Analysis Comparing Growth and GH Therapy Response in IGF1R Mutation Carriers and SGA Children.

CONTEXT: IGF1 receptor mutations (IGF1RM) are rare; however, patients exhibit pronounced growth retardation without catch-up. Although several case reports exist, a comprehensive statistical analysis investigating growth profile and benefit of recombinant human growth hormone (rhGH) treatment is still missing. OBJECTIVE AND METHODS: Here, we compared IGF1RM carriers (n = 23) retrospectively regarding birth parameters, growth response to rhGH therapy, near final height, and glucose/insulin homeostasis to treated children born small for gestational age (SGA) (n = 34). Additionally, health profiles of adult IGF1RM carriers were surveyed by a questionnaire. RESULTS: IGF1RM carriers were significantly smaller at rhGH initiation and had a diminished first-year response compared to SGA children (Δ height standard deviation score: 0.29 vs. 0.65), resulting in a lower growth response under therapy. Interestingly, the number of poor therapy responders was three times higher for IGF1RM carriers than for SGA patients (53 % vs. 17 %). However, most IGF1RM good responders showed catch-up growth to the levels of SGA patients. Moreover, we observed no differences in homeostasis model assessment of insulin resistance before treatment, but during treatment insulin resistance was significantly increased in IGF1RM carriers compared to SGA children. Analyses in adult mutation carriers indicated no increased occurrence of comorbidities later in life compared to SGA controls. CONCLUSION: In summary, IGF1RM carriers showed a more pronounced growth retardation and lower response to rhGH therapy compared to non-mutation carriers, with high individual variability. Therefore, a critical reevaluation of success should be performed periodically. In adulthood, we could not observe a significant influence of IGF1RM on metabolism and health of carriers.

IGF signaling defects as causes of growth failure and IUGR.

A substantial portion of children born small for gestational age (SGA) fail to catch up height, despite normal or even elevated insulin-like growth factor (IGF1) serum levels. In most cases, the etiology of the apparent IGF1 resistance is regarded as idiopathic. However, the recent identification of human IGF1 and IGF1 receptor (IGF1R) mutations, as well as information obtained from transgenic animals, points to a strong genetic component being of pivotal importance in the development of growth retardation. These findings direct attention to molecules downstream of the IGF1R, which have both growth-promoting and, to a lesser extent, metabolic functions. Therefore, defects in these molecules are likely to participate in the etiology of human SGA.

IGF1R Gene Alterations in Children Born Small for Gestitional Age (SGA).

BACKGROUND: Small for gestational age (SGA)-born children are a heterogeneous group with few genetic causes reported. Genetic alterations in the IGF1 receptor (IGF1R) are found in some SGA children. AIM: To investigate whether alterations in IGF1R gene are present in SGA born children. PATIENTS AND METHODS: We analysed 64 children born SGA who stayed short (mean -3.25 ± 0.9 SDS) within the first 4 years of age, and 36 SGA children who caught up growth (0.20 ± 1.1 SDS). PCR products of all coding IGF1R exons were screened by dHPLC followed by direct sequencing of conspicuous fragments to identify small nucleotide variants. The presence of IGF1R gene copy number alterations was determined by Multiplex Ligation-dependent Probe Amplification (MLPA). RESULTS: The cohort of short SGA born children revealed a heterozygous, synonymous variant c.3453C > T in one patient and a novel heterozygous 3 bp in-frame deletion (c.3234_3236delCAT) resulting in one amino acid deletion (p.Ile1078del) in another patient. The first patient had normal serum levels of IGF1. The second patient had unusually low IGF1 serum concentrations (-1.57 SD), which contrasts previously published data where IGF1 levels rarely are found below the age-adjusted mean. CONCLUSIONS: IGF1R gene alterations were present in 2 of 64 short SGA children. The patients did not have any dysmorphic features or developmental delay. It is remarkable that one of them had significantly decreased serum concentrations of IGF1. Growth response to GH treatment in one of the patients was favourable, while the second one discontinued the treatment, but with catch-up growth.

Novel Mutations in the Asparagine Synthetase Gene (ASNS) Associated With Microcephaly.

Microcephaly is a devastating condition defined by a small head and small brain compared to the age- and sex-matched population. Mutations in a number of different genes causative for microcephaly have been identified, e.g., MCPH1, WDR62, and ASPM. Recently, mutations in the gene encoding the enzyme asparagine synthetase (ASNS) were associated to microcephaly and so far 24 different mutations in ASNS causing microcephaly have been described. In a family with two affected girls, we identified novel compound heterozygous variants in ASNS (c.1165G > C, p.E389Q and c.601delA, p.M201Wfs∗28). The first mutation (E389Q) is a missense mutation resulting in the replacement of a glutamate residue evolutionary conserved from Escherichia coli to Homo sapiens by glutamine. Protein modeling based on the known crystal structure of ASNS of E. coli predicted a destabilization of the protein by E389Q. The second mutation (p.M201Wfs∗28) results in a premature stop codon after amino acid 227, thereby truncating more than half of the protein. The novel variants expand the growing list of microcephaly causing mutations in ASNS.

Dominant-negative STAT5B mutations cause growth hormone insensitivity with short stature and mild immune dysregulation.

Growth hormone (GH) insensitivity syndrome (GHIS) is a rare clinical condition in which production of insulin-like growth factor 1 is blunted and, consequently, postnatal growth impaired. Autosomal-recessive mutations in signal transducer and activator of transcription (STAT5B), the key signal transducer for GH, cause severe GHIS with additional characteristics of immune and, often fatal, pulmonary complications. Here we report dominant-negative, inactivating STAT5B germline mutations in patients with growth failure, eczema, and elevated IgE but without severe immune and pulmonary problems. These STAT5B missense mutants are robustly tyrosine phosphorylated upon stimulation, but are unable to nuclear localize, or fail to bind canonical STAT5B DNA response elements. Importantly, each variant retains the ability to dimerize with wild-type STAT5B, disrupting the normal transcriptional functions of wild-type STAT5B. We conclude that these STAT5B variants exert dominant-negative effects through distinct pathomechanisms, manifesting in milder clinical GHIS with general sparing of the immune system.

IGF-I receptor mutations resulting in intrauterine and postnatal growth retardation.

BACKGROUND: Approximately 10 percent of infants with intrauterine growth retardation remain small, and the causes of their growth deficits are often unclear. We postulated that mutations in the gene for the insulin-like growth factor I receptor (IGF-IR) might underlie some cases of prenatal and postnatal growth failure. METHODS: We screened two groups of children for abnormalities in the IGF-IR gene. In one group of 42 patients with unexplained intrauterine growth retardation and subsequent short stature, we used single-strand conformation polymorphism analysis, followed by direct DNA sequencing of any abnormalities found. A second cohort consisted of 50 children with short stature who had elevated circulating IGF-I concentrations. Complete sequencing of the IGF-IR gene was performed with DNA from nine children. We also studied a control group of 43 children with normal birth weights. RESULTS: In the first cohort, we identified one girl who was a compound heterozygote for point mutations in exon 2 of the IGF-IR gene that altered the amino acid sequence to Arg108Gln in one allele and Lys115Asn in the other. Fibroblasts cultured from the patient had decreased IGF-I-receptor function, as compared with that in control fibroblasts. No such mutations were found in the 43 controls. In the second group, we identified one boy with a nonsense mutation (Arg59stop) that reduced the number of IGF-I receptors on fibroblasts. Both children had intrauterine growth retardation and poor postnatal growth. CONCLUSIONS: Mutations in the IGF-IR gene that lead to abnormalities in the function or number of IGF-I receptors may also retard intrauterine and subsequent growth in humans.

Functional and clinical relevance of novel and known PCSK1 variants for childhood obesity and glucose metabolism.

OBJECTIVE: Variants in Proprotein Convertase Subtilisin/Kexin Type 1 (PCSK1) may be causative for obesity as suggested by monogenic cases and association studies. Here we assessed the functional relevance in experimental studies and the clinical relevance through detailed metabolic phenotyping of newly identified and known PCSK1 variants in children. RESULTS: In 52 obese children selected for elevated proinsulin levels and/or impaired glucose tolerance, we found eight known variants and two novel heterozygous variants (c.1095 + 1G > A and p.S24C) by sequencing the PCSK1 gene. Patients with the new variants presented with extreme obesity, impaired glucose tolerance, and PCOS. Functionally, c.1095 + 1G > A caused skipping of exon8 translation and a complete loss of enzymatic activity. The protein was retained within the endoplasmic reticulum (ER) causing ER stress. The p.S24C variant had no functional effect on protein size, cell trafficking, or enzymatic activity. The known variants rs6230, rs35753085, and rs725522 in the 5' end did not affect PCSK1 promoter activity. In clinical association studies in 1673 lean and obese children, we confirmed associations of rs6232 and rs6234 with BMI-SDS and of rs725522 with glucose stimulated insulin secretion and Matsuda index. We did not find the new variants in any other subjects. CONCLUSIONS: We identified and functionally characterized two rare novel PCSK1 variants of which c.1095 + 1G > A caused complete loss of protein function. In addition to confirming rs6232 and rs6234 in PCSK1 as polygenic risk variants for childhood obesity, we describe an association of rs725522 with insulin metabolism. Our results support the contribution of PCSK1 variants to obesity predisposition in children.

Copy number variations in "classical" obesity candidate genes are not frequently associated with severe early-onset obesity in children.

BACKGROUND: Obesity is genetically heterogeneous and highly heritable, although polymorphisms explain the phenotype in only a small proportion of obese children. We investigated the presence of copy number variations (CNVs) in "classical" genes known to be associated with (monogenic) early-onset obesity in children. METHODS: In 194 obese Caucasian children selected for early-onset and severe obesity from our obesity cohort we screened for deletions and/or duplications by multiplex ligation-dependent probe amplification reaction (MLPA). As we found one MLPA probe to interfere with a polymorphism in SIM1 we investigated its association with obesity and other phenotypic traits in our extended cohort of 2305 children. RESULTS: In the selected subset of most severely obese children, we did not find CNV with MLPA in POMC, LEP, LEPR, MC4R, MC3R or MC2R genes. However, one SIM1 probe located at exon 9 gave signals suggestive for SIM1 insufficiency in 52 patients. Polymerase chain reaction (PCR) analysis identified this as a false positive result due to interference with single nucleotide polymorphism (SNP) rs3734354/rs3734355. We, therefore, investigated for associations of this polymorphism with obesity and metabolic traits in our extended cohort. We found rs3734354/rs3734355 to be associated with body mass index-standard deviation score (BMI-SDS) (p = 0.003), but not with parameters of insulin metabolism, blood pressure or food intake. CONCLUSIONS: In our modest sample of severely obese children, we were unable to find CNVs in well-established monogenic obesity genes. Nevertheless, we found an association of rs3734354 in SIM1 with obesity of early-onset type in children, although not with obesity-related traits.

Evidence against a direct effect of leptin on insulin-like growth factor-I (IGF-I), IGFBP-2 and IGF-I receptor expression in human SK-N-MC neuroepithelioma cells.

The ob gene product, leptin, is synthesized by adipocytes. In rodents, its main role is to regulate energy expenditure and food intake. The growth hormone (GH)-insulin-like growth factor (IGF) system is also ubiquitously expressed, is also involved in energy homeostasis and shares some of the signaling molecules of leptin and its receptors. Therefore, we have asked whether or not leptin interacts with the GH-IGF system in an in vitro model. SK-N-MC cells were chosen for further investigation since they express IGF-I, IGF-I receptor and IGFBP-2 mRNA and secrete IGF-I and IGFBP-2 protein. Specific leptin receptor mRNA, both short and long isoform transcripts, were identified in SK-N-MC cells by RT-PCR. Secondly and most importantly, when SK-N-MC cells were cultured in the presence of leptin, neither IGF-I, nor IGF-I receptor or IGFBP-2 mRNA expression was different than in the absence of leptin. In addition, an increase in leptin did not alter secretion of immunoreactive IGF-I or IGFBP-2 protein into cell culture medium. In conclusion, (1) human SK-N-MC neuroepithelioma cells express ob and leptin receptor mRNA and secrete leptin. (2) Added exogenous leptin does not affect IGF-I, IGFBP-2 or IGF-I receptor mRNA expression and IGF-I and IGFBP-2 secretion by SK-N-MC cells in vitro under the conditions studied. We hypothesize that leptin and the IGF system do not interact directly in a cell culture model of neuroepithelioma cells.

Obesity in childhood and adolescence: a review in the interface between adipocyte physiology and clinical challenges.

Body weight is regulated by a feedback loop in which peripheral signals report nutritional information to an integratory center in the brain. The cloning of the ob gene is consistent with this concept and suggests that body fat content in adult rodents is regulated by a negative feedback loop centered in the hypothalamus. In recent years a number of additional signaling molecules secreted by adipose tissue have been discovered. These hormones, named adipocytokines, include resistin, adiponectin, and visfatin. Among the adipocytokines, adiponectin is perhaps the most interesting compound for the clinician since low adiponectin serum levels have been found in obese subjects and in particular in insulin resistant subjects. The definition and diagnosis of obesity in children and adolescents are surprisingly difficult. The level of fatness at which morbidity increases is determined on an acturial basis. In children and adolescents the degree of body fat mass depends upon ethnic background , gender, developmental stage, and age. Treatment and prevention of obesity in childhood and adolescence are major challenges for today's health care providers and societies.

Novel heterozygous IGF1R mutation in two brothers with developing impaired glucose tolerance.

Infants born small for gestational age (SGA) are at risk to develop metabolic complications. Insulin-like growth factor 1 (IGF-1) resistance due to IGF-1 receptor (IGF1R) mutations is a rare genetic condition that causes proportionate growth retardation. The contribution of an impaired IGF1R function to the development of comorbidities such as disturbed glucose homeostasis is not well understood. Genetic analysis and detailed auxological, endocrine and psychological investigations in two male SGA siblings were performed. The two patients and their father bear a novel heterozygous mutation (p.Cys1248Tyr) in the IGF1R gene. Both brothers displayed very similar growth pattern before and during recombinant human growth hormone treatment, whereas oral glucose tolerance tests showed variable manifestations of progressive impaired glucose tolerance. The father had already developed type 2 diabetes mellitus. Growth retardation in our patients is likely caused by the IGF1R mutation that might predispose to disturbances of carbohydrate homeostasis. Therefore, a close metabolic monitoring of affected patients is indicated, particularly if growth hormone therapy is commenced.

Homozygous mutation of the IGF1 receptor gene in a patient with severe pre- and postnatal growth failure and congenital malformations.

BACKGROUND: Heterozygous mutations in the IGF1 receptor (IGF1R) gene lead to partial resistance to IGF1 and contribute to intrauterine growth retardation (IUGR) with postnatal growth failure. To date, homozygous mutations of this receptor have not been described. SUBJECT: A 13.5-year-old girl born from healthy first-cousin parents presented with severe IUGR and persistent short stature. Mild intellectual impairment, dysmorphic features, acanthosis nigricans, and cardiac malformations were also present. METHODS: Auxological and endocrinological profiles were measured. All coding regions of the IGF1R gene including intron boundaries were amplified and directly sequenced. Functional characterization was performed by immunoblotting using patient's fibroblasts. RESULTS: IGF1 level was elevated at 950NG/ML (+7 S.D.). Fasting glucose level was normal associated with high insulin levels at baseline and during an oral glucose tolerance test. Fasting triglyceride levels were elevated. sequencing of the IGF1R gene led to the identification of a homozygous variation in exon 2: c.119G>T (p.Arg10Leu). As a consequence, IGF1-dependent receptor autophosphorylation and downstream signaling were reduced in patient's fibroblasts. Both parents were heterozygous for the mutation. CONCLUSION: The homozygous mutation of the IGF1R is associated with severe IUGR, dysmorphic features, and insulin resistance, while both parents were asymptomatic heterozygous carriers of the same mutation.

Alu-mediated recombination defect in IGF1R: haploinsufficiency in a patient with short stature.

BACKGROUND: The insulin-like growth factor (IGF) receptor (IGF1R) is essential for normal development and growth. IGF1R mutations cause IGF-1 resistance resulting in intrauterine and postnatal growth failure. The phenotypic spectrum related to IGF1R mutations remains to be fully understood. METHODS: Auxological and endocrinological data of a patient identified previously were assessed. The patient's fibroblasts were studied to characterize the IGF1R deletion, mRNA fate, protein expression and signalling capabilities. RESULTS: The boy, who carries a heterozygous IGF1R exon 6 deletion caused by Alu element-mediated recombination and a heterozygous SHOX variant (p.Met240Ile), was born appropriate for gestational age but developed proportionate short stature postnatally. IGF-1 levels were low-normal. None of the stigmata associated with SHOX deficiency or sporadically observed in IGF1R mutation carriers were present. Nonsense-mediated mRNA decay led to a substantial decline of IGF1R dosage and IGF-1-dependent receptor autophosphorylation but not impaired downstream signalling. CONCLUSION: We present the first detailed report of an intragenic IGF1R deletion identified in a patient who, apart from short stature, deviates from all established markers that qualify a growth-retarded child for IGF1R analysis. Although such children will usually escape routine clinical mutation screenings, they can contribute to the understanding of factors and mechanisms that cooperate with the IGF1R.