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.

A new p.(Ile66Serfs*93) IGF2 variant is associated with pre- and postnatal growth retardation

Objective The IGF/IGF1R axis is involved in the regulation of human growth. Both IGF1 and IGF2 can bind to the IGF1R in order to promote growth via the downstream PI3K/AKT pathway. Pathogenic mutations in IGF1 and IGF1R determine intrauterine growth restriction and affect postnatal body growth. However, to date, there are only few reports of pathogenic IGF2 mutations causing severe prenatal, as well as postnatal growth retardation. Results Here we describe a de novo c.195delC IGF2 variant (NM_000612, p.(Ile66Serfs*93)) in a 4-year-old patient with severe pre- and post-natal growth retardation in combination with dystrophy, facial dimorphism, finger deformities, as well as a patent ductus. Cloning and sequencing of a long-range PCR product harboring the deletion and a SNP informative site chr11:2153634 (rs680, NC_000011.9:g.2153634T>C) demonstrated that the variant resided on the paternal allele. This finding is consistent with the known maternal imprinting of IGF2. 3D protein structure prediction and overexpression studies demonstrated that the p.(Ile66Serfs*93) IGF2 gene variation resulted in an altered protein structure that impaired ligand/receptor binding and thus prevents IGF1R activation. Conclusion The severity of the phenotype in combination with the dominant mode of transmission provides further evidence for the involvement of IGF2 in growth disorders.

A new p.(Ile66Serfs*93) IGF2 variant is associated with pre- and postnatal growth retardation

Objective The IGF/IGF1R axis is involved in the regulation of human growth. Both IGF1 and IGF2 can bind to the IGF1R in order to promote growth via the downstream PI3K/AKT pathway. Pathogenic mutations in IGF1 and IGF1R determine intrauterine growth restriction and affect postnatal body growth. However, to date, there are only few reports of pathogenic IGF2 mutations causing severe prenatal, as well as postnatal growth retardation. Results Here we describe a de novo c.195delC IGF2 variant (NM_000612, p.(Ile66Serfs*93)) in a 4-year-old patient with severe pre- and post-natal growth retardation in combination with dystrophy, facial dimorphism, finger deformities, as well as a patent ductus. Cloning and sequencing of a long-range PCR product harboring the deletion and a SNP informative site chr11:2153634 (rs680, NC_000011.9:g.2153634T>C) demonstrated that the variant resided on the paternal allele. This finding is consistent with the known maternal imprinting of IGF2. 3D protein structure prediction and overexpression studies demonstrated that the p.(Ile66Serfs*93) IGF2 gene variation resulted in an altered protein structure that impaired ligand/receptor binding and thus prevents IGF1R activation. Conclusion The severity of the phenotype in combination with the dominant mode of transmission provides further evidence for the involvement of IGF2 in growth disorders.

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.

Severe growth hormone insensitivity syndrome (GHIS) with immunodeficiency is caused by autosomal recessive mutations in STAT5B. Here the authors report heterozygous STAT5B mutations with dominant-negative effects, causing mild GHIS without immune defects.

Regulation of human adipogenesis by miR125b-5p

MicroRNAs (miRNAs) are non-coding RNAs that regulate target gene expression at the post-transcriptional level and are supposed to be implicated in the control of adipogenesis. We aimed to identify miRNAs which are involved in the regulation of human adipogenesis and searched for their molecular targets. Applying microarray-analysis we identified miR125b-5p as upregulated during human adipocyte differentiation, although its role during adipogenesis is unknown. We identified and characterized the matrix metalloproteinase 11 (MMP11) as a direct target of miR125b-5p by showing that miR125b-5p overexpression significantly reduces MMP11 luciferase activity and mutation of any single binding site was sufficient to abolish the miR125b-5p mediated inhibition of luciferase activity. MMP11 overexpression decreased fat accumulation, indicating that MMP11 acts as an anti-adipogenic regulator. In contrast, overexpression of miR125b-5p itself reduced adipogenesis. In summary, we identified miR125b-5p as upregulated during human adipogenesis indicating that miR125b-5p may serve as a regulator of human adipocyte differentiation. We further show that miR125b-5p downregulates the anti-adipogenic MMP11, but directly inhibits adipogenesis itself. Taken together, these data implicate that miR125b-5p can affect human adipogenesis via MMP11 and probably additional targets.

Evidence of early alterations in adipose tissue biology and function and its association with obesity-related inflammation and insulin resistance in children

Accumulation of fat mass in obesity may result from hypertrophy and/or hyperplasia and is frequently associated with adipose tissue (AT) dysfunction in adults. Here we assessed early alterations in AT biology and function by comprehensive experimental and clinical characterization of 171 AT samples from lean and obese children aged 0 to 18 years. We show an increase in adipocyte size and number in obese compared with lean children beginning in early childhood. These alterations in AT composition in obese children were accompanied by decreased basal lipolytic activity and significantly enhanced stromal vascular cell proliferation in vitro, potentially underlying the hypertrophy and hyperplasia seen in obese children, respectively. Furthermore, macrophage infiltration, including the formation of crown-like structures, was increased in AT of obese children from 6 years on and was associated with higher hs-CRP serum levels. Clinically, adipocyte hypertrophy was not only associated with leptin serum levels but was highly and independently correlated with HOMA-IR as a marker of insulin resistance in children. In summary, we show that adipocyte hypertrophy is linked to increased inflammation in AT in obese children, thereby providing evidence that obesity-associated AT dysfunction develops in early childhood and is related to insulin resistance.

Direct evidence of brown adipocytes in different fat depots in children

Recent studies suggested the persistence of brown adipocytes in adult humans, as opposed to being exclusively present in infancy. In this study, we investigated the presence of brown-like adipocytes in adipose tissue (AT) samples of children and adolescents aged 0 to 18 years and evaluated the association with age, location, and obesity. For this, we analysed AT samples from 131 children and 23 adults by histological, immunohistochemical and expression analyses. We detected brown-like and UCP1 positive adipocytes in 10.3% of 87 lean children (aged 0.3 to 10.7 years) and in one overweight infant, whereas we did not find brown adipocytes in obese children or adults. In our samples, the brown-like adipocytes were interspersed within white AT of perirenal, visceral and also subcutaneous depots. Samples with brown-like adipocytes showed an increased expression of UCP1 (>200fold), PRDM16 (2.8fold), PGC1α and CIDEA while other brown/beige selective markers, such as PAT2, P2RX5, ZIC1, LHX8, TMEM26, HOXC9 and TBX1 were not significantly different between UCP1 positive and negative samples. We identified a positive correlation between UCP1 and PRDM16 within UCP1 positive samples, but not with any other brown/beige marker. In addition, we observed significantly increased PRDM16 and PAT2 expression in subcutaneous and visceral AT samples with high UCP1 expression in adults. Our data indicate that brown-like adipocytes are present well beyond infancy in subcutaneous depots of non-obese children. The presence was not restricted to typical perirenal locations, but they were also interspersed within WAT of visceral and subcutaneous depots.