Philip G. Murray

Growth hormone, the insulin-like growth factor axis, insulin and cancer risk

Growth hormone (GH), insulin-like growth factor (IGF)-I and insulin have potent growth-promoting and anabolic actions. Their potential involvement in tumor promotion and progression has been of concern for several decades. The evidence that GH, IGF-I and insulin can promote and contribute to cancer progression comes from various sources, including transgenic and knockout mouse models and animal and human cell lines derived from cancers. Assessments of the GH–IGF axis in healthy individuals followed up to assess cancer incidence provide direct evidence of this risk; raised IGF-I levels in blood are associated with a slightly increased risk of some cancers. Studies of human diseases characterized by excess growth factor secretion or treated with growth factors have produced reassuring data, with no notable increases in de novo cancers in children treated with GH. Although follow-up for the vast majority of these children does not yet extend beyond young adulthood, a slight increase in cancers in those with long-standing excess GH secretion (as seen in patients with acromegaly) and no overall increase in cancer with insulin treatment, have been observed. Nevertheless, long-term surveillance for cancer incidence in all populations exposed to increased levels of GH is vitally important.

Exome sequencing identifies CCDC8 mutations in 3-M syndrome, suggesting that CCDC8 contributes in a pathway with CUL7 and OBSL1 to control human growth

3-M syndrome, a primordial growth disorder, is associated with mutations in CUL7 and OBSL1. Exome sequencing now identifies mutations in CCDC8 as a cause of 3-M syndrome. CCDC8 is a widely expressed gene that is transcriptionally associated to CUL7 and OBSL1, and coimmunoprecipitation indicates a physical interaction between CCDC8 and OBSL1 but not CUL7. We propose that CUL7, OBSL1, and CCDC8 are members of a pathway controlling mammalian growth.

The Primordial Growth Disorder 3-M Syndrome Connects Ubiquitination to the Cytoskeletal Adaptor OBSL1

3-M syndrome is an autosomal-recessive primordial growth disorder characterized by significant intrauterine and postnatal growth restriction. Mutations in the CUL7 gene are known to cause 3-M syndrome. In 3-M syndrome patients that do not carry CUL7 mutations, we performed high-density genome-wide SNP mapping to identify a second locus at 2q35-q36.1. Further haplotype analysis revealed a 1.29 Mb interval in which the underlying gene is located and we subsequently discovered seven distinct null mutations from 10 families within the gene OBSL1. OBSL1 is a putative cytoskeletal adaptor protein that localizes to the nuclear envelope. We were also able to demonstrate that loss of OBSL1 leads to downregulation of CUL7, implying a role for OBSL1 in the maintenance of CUL7 protein levels and suggesting that both proteins are involved within the same molecular pathway.

Controversies in the diagnosis and management of growth hormone deficiency in childhood and adolescence

Growth hormone deficiency (GHD) is a rare but important cause of short stature in childhood with a prevalence of 1 in 4000. The diagnosis is currently based on an assessment of auxology along with supporting evidence from biochemical and neuroradiological studies. There are significant controversies in the diagnosis and management of GHD. Growth hormone (GH) stimulation tests continue to play a key role in GHD diagnosis but the measured GH concentration can vary significantly with stimulation test and GH assay used, creating difficulties for diagnostic accuracy. Such issues along with the use of adjunct biochemical markers such as IGF-I and IGFBP-3 for the diagnosis of GHD, will be discussed in this review. Additionally, the treatment of GHD remains a source of much debate; there is no consensus on the best mechanism for determining the starting dose of GH in patients with GHD. Weight and prediction based models will be discussed along with different mechanisms for dose adjustment during treatment (auxology or IGF-I targeting approaches). At the end of growth and childhood treatment, many subjects diagnosed with isolated GHD re-test normal. It is not clear if this represents a form of transient GHD or a false positive diagnosis during childhood. Given the difficulties inherent in the diagnosis of GHD, an early reassessment of the diagnosis in those who respond poorly to GH is to be recommended.

Endocrine Control of Growth.

Human growth is a complex process starting at conception and completing in adolescence at the time of growth plate fusion. Growth can be divided into four phases: (1) fetal, where the predominant endocrine factors controlling growth are insulin and the insulin‐like growth factors. (2) Infancy, where growth is mainly dependent upon nutrition. (3) Childhood, where the growth hormone–insulin‐like growth factor‐I (GH‐IGF‐I) axis and thyroid hormone are most important. (4) Puberty, where along with the GH‐IGF‐I axis the activation of the hypothalamo‐pituitary–gonadal axis to generate sex steroid secretion becomes vital to the completion of growth. GH is released from the pituitary in a pulsatile fashion under the control of GHRH, Ghrelin, and somatostatin and, via a complex signal transduction cascade, initiates the release of IGF‐I within many tissues but predominantly the liver and at the growth plate. IGF‐I acts in an autocrine and paracrine manner via the IGF‐I receptor to stimulate cell proliferation and longitudinal growth. Activation of the pituitary–gonadal axis during puberty occurs via a complex interaction of factors including kisspeptin, leptin, gonadotrophin releasing hormone, and tachykinin ultimately leading to augmentation of GH secretion, the pubertal growth spurt, and fusion of the growth plates. Many other hormones can affect the GH‐IGF‐I system or directly affect cell proliferation at the growth plate including thyroid hormone, vitamin D, and corticosteroids.

Maternal age in patients with septo-optic dysplasia

AIM To determine whether patients with septooptic dysplasia (SOD) are of normal birth weight and gestation but are born to mothers who are significantly younger than average. METHODS Retrospective study of 30 patients with SOD attending the Royal Hospital for Sick Children, Glasgow. Birth data for the Scottish population were used for comparison. RESULTS Mean birth weight was 3.42 (range 2.66-4.18) kg. One patient was born preterm while the rest were born at term. Data for the Scottish population were available from 1979 onwards and 26 patients born after this year were selected for analysis. Median maternal age in this group was 21 (range 16-41) years, significantly lower than the median maternal age for Scotland of 27.12 (range 25.8-28.6) years (95% CI 4.8-8.0 years). CONCLUSION Patients with SOD are of normal birth weight and gestation but are born to mothers who are significantly younger than average.

Exploring the spectrum of 3-M syndrome, a primordial short stature disorder of disrupted ubiquitination

3‐M syndrome is an autosomal recessive primordial growth disorder characterized by small birth size and post‐natal growth restriction associated with a spectrum of minor anomalies (including a triangular‐shaped face, flat cheeks, full lips, short chest and prominent fleshy heels). Unlike many other primordial short stature syndromes, intelligence is normal and there is no other major system involvement, indicating that 3‐M is predominantly a growth‐related condition. From an endocrine perspective, serum GH levels are usually normal and IGF‐I normal or low, while growth response to rhGH therapy is variable but typically poor. All these features suggest a degree of resistance in the GH‐IGF axis. To date, mutations in three genes CUL7, OBSL1 and CCDC8 have been shown to cause 3‐M. CUL7 acts an ubiquitin ligase and is known to interact with p53, cyclin D‐1 and the growth factor signalling molecule IRS‐1, the link with the latter may contribute to the GH‐IGF resistance. OBSL1 is a putative cytoskeletal adaptor that interacts with and stabilizes CUL7. CCDC8 is the newest member of the pathway and interacts with OBSL1 and, like CUL7, associates with p53, acting as a co‐factor in p53‐medicated apoptosis. 3‐M patients without a mutation have also been identified, indicating the involvement of additional genes in the pathway. Potentially damaging sequence variants in CUL7 and OBSL1 have been identified in idiopathic short stature (ISS), including those born small with failure of catch‐up growth, signifying that the 3‐M pathway could play a wider role in disordered growth.

Mutations in CUL7, OBSL1 and CCDC8 in 3-M syndrome lead to disordered growth factor signalling

3-M syndrome is a primordial growth disorder caused by mutations in CUL7, OBSL1 or CCDC8. 3-M patients typically have a modest response to GH treatment, but the mechanism is unknown. Our aim was to screen 13 clinically identified 3-M families for mutations, define the status of the GH-IGF axis in 3-M children and using fibroblast cell lines assess signalling responses to GH or IGF1. Eleven CUL7, three OBSL1 and one CCDC8 mutations in nine, three and one families respectively were identified, those with CUL7 mutations being significantly shorter than those with OBSL1 or CCDC8 mutations. The majority of 3-M patients tested had normal peak serum GH and normal/low IGF1. While the generation of IGF binding proteins by 3-M cells was dysregulated, activation of STAT5b and MAPK in response to GH was normal in CUL7(-/-) cells but reduced in OBSL1(-/-) and CCDC8(-/-) cells compared with controls. Activation of AKT to IGF1 was reduced in CUL7(-/-) and OBSL1(-/-) cells at 5 min post-stimulation but normal in CCDC8(-/-) cells. The prevalence of 3-M mutations was 69% CUL7, 23% OBSL1 and 8% CCDC8. The GH-IGF axis evaluation could reflect a degree of GH resistance and/or IGF1 resistance. This is consistent with the signalling data in which the CUL7(-/-) cells showed impaired IGF1 signalling, CCDC8(-/-) cells showed impaired GH signalling and the OBSL1(-/-) cells showed impairment in both pathways. Dysregulation of the GH-IGF-IGF binding protein axis is a feature of 3-M syndrome.

The genetics of 3-M syndrome: unravelling a potential new regulatory growth pathway

3-M syndrome is an autosomal recessive primordial growth disorder characterised by severe postnatal growth restriction caused by mutations in CUL7, OBSL1 or CCDC8. Clinical characteristics include dysmorphic facial features and fleshy prominent heels with a variable degree of radiological abnormalities. CUL7 is a structural protein central to the formation of an ubiquitin E3 ligase that is known to target insulin receptor substrate 1 for degradation. CUL7 also binds to p53 and may be involved in the control of p53-dependent apoptosis. OBSL1 is a cytoskeletal adaptor protein that was thought to play a central role in myocyte remodelling, and CCDC8 has no defined function as yet. However, the physical interaction of OBSL1 with both CUL7 and CCDC8 and its potential role in the regulation of CUL7 expression suggest all three proteins are members of the same growth-regulatory pathway. Future work should be directed to investigating the function of the 3-M syndrome pathway and in particular the role in the insulin like growth factor I signalling pathway with a view of potentially revealing new therapeutic targets and identifying key regulators of cellular growth.

Associations with multiple pituitary hormone deficiency in patients with an ectopic posterior pituitary gland

Introduction  The presence of an ectopic posterior pituitary gland (EPP) on magnetic resonance imaging (MRI) is associated with hypopituitarism with one or more hormone deficiencies. We aimed to identify risk factors for having multiple pituitary hormone deficiency (MPHD) compared to isolated growth hormone deficiency (IGHD) in patients with an EPP.