Childhood-onset growth hormone deficiency, cognitive function and brain N-acetylaspartate

Prenatal exposure to endocrine disrupting chemicals is associated with altered DNA methylation in cord blood

Prenatal exposure to endocrine disrupting chemicals can interfere with development, and has been associated with social-cognitive functioning and adverse health outcomes later in life. Exposure-associated changes of DNA methylation (DNAm) patterns have been suggested as a possible mediator of this relationship. This study investigated whether prenatal low-dose exposure to polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) is associated with altered DNAm patterns across the genome in a Western urban-industrial population. In 142 mother-infant pairs from the Duisburg Birth Cohort Study, PCBs and PCDD/Fs levels were quantified from maternal blood during late pregnancy and associated with DNAm levels in cord blood using the Illumina EPIC beadchip. The epigenome-wide association studies (EWAS) identified 32 significantly differentially methylated positions (DMPs) and eight differentially methylated regions (DMRs) associated with six congeners of PCB and PCDD in females or males (FDRs < 0.05). DMPs and DMRs mapped to genes involved in neurodevelopment, gene regulation, and immune functioning. Weighted gene correlation network analysis (WGCNA) showed 31 co-methylated modules (FDRs < 0.05) associated with one congener of PCDF levels in females. Results of both analytical strategies indicate that prenatal exposure to PCBs and PCDD/Fs is associated with altered DNAm of genes involved in neurodevelopment, gene expression and immune functioning. DNAm and gene expression levels of several of these genes were previously associated with EDC exposure in rodent models. Follow-up studies will clarify whether these epigenetic changes might contribute to the origin for adverse mental and health outcomes.

Psychological well-being and illness perceptions in patients with hypopituitarism

OBJECTIVE

The primary aim of the current study was to objectify a spectrum of persisting subjective psychological complaints in patients with hypopituitarism, at least six months after normalizing of the hormonal disturbances. Also, gender differences on these outcomes were investigated. The secondary aim was to identify illness perceptions and causal attributions within this patient group.

METHODS

A total of 42 adult participants (60% females) with treated hypopituitarism once filled out a number of psychological questionnaires. The Profile of Mood States (POMS) and the Hospital Anxiety and Depression Scale (HADS) assessed mood and the Symptom Checklist-90 (SCL-90) and the Work and Social Adjustment Scale (WSAS) assessed well-being. Illness perceptions were identified using the Illness Perceptions Questionnaire-Brief Dutch Language Version (IPQ-B DLV) and causal attributions by using the Causal Attribution List (CAL). Patient outcomes were compared to reference values of healthy norm groups.

RESULTS

Participants scored significantly worse on the POMS depression, anger, fatigue and tension subscales, the SCL-90 psychoneuroticism, depression, inadequacy of thinking and acting and sleeping problems subscales and all subscales of the WSAS when compared to reference data. Women also scored worse on depression (HADS) and somatic symptoms (SCL-90). Compared to other illnesses, patients with hypopituitarism have more negative and realistic illness perceptions on consequences, timeline, identity and emotions. Participants attributed their complaints more to physical causes than psychological causes.

CONCLUSION

Despite normalization of hormonal disturbances, patients with hypopituitarism in general can still experience problems during daily living, such as negative mood states and a decreased psychological well-being.

Spirulina Enhances Bone Modeling in Growing Male Rats by Regulating Growth-Related Hormones

In recent years, growth hormone deficiency in children has been treated with hormone therapy despite the possible significant side effects. Therefore, it was deemed beneficial to develop functional foods or dietary supplements for safely improving children's growth. Spirulina platensis is known for its high antioxidant, anti-aging, anti-cancer, and immunity-enhancing properties, as well as its high digestibility and high protein content, but little has been reported about its influence on bone development in children with a normal supply of protein. In this study, we evaluated the effects of spirulina on the bone metabolism and antioxidant profiles of three-week-old growing male rats. The animals were divided into four groups (n = 17 per group) and were fed AIN93G diets with 0% (control), 30% (SP30), 50% (SP50), and 70% (SP70) of casein protein replaced by spirulina, respectively, for seven weeks. We observed that spirulina enhanced bone growth and bone strength by stimulating parathyroid hormone and growth hormone activities, as well its increased antioxidant activity. These results indicate that spirulina provides a suitable dietary supplement and alternative protein source with antioxidant benefits for growth improvement in early developmental stages.

The enigmatic role of growth hormone in age-related diseases, cognition, and longevity

Growth hormone (GH) is secreted by the anterior pituitary gland and regulates various metabolic processes throughout the body. GH and IGF-1 levels are markedly reduced in older humans, leading some to hypothesize GH supplementation could be a viable "anti-aging" therapy. However, there is still much debate over the benefits and risks of GH administration. While an early study of GH administration reported reduced adiposity and lipid levels and increased bone mineral density, subsequent studies failed to show significant benefits. Conversely, other studies found positive effects of GH deficiency including extended life span, improved cognitive function, resistance to diseases such as cancer and diabetes, and improved insulin sensitivity despite a higher fat percentage. Thus, the roles of GH in aging and cognition remain unclear, and there is currently not enough evidence to support use of GH as an anti-aging or cognitive impairment therapy. Additional robust and longer-duration studies of efficacy and safety of GH administration are needed to determine if modulating GH levels could be a successful strategy for treating aging and age-related diseases.

Insulin-like Growth Factor 1 (IGF-1) as a marker of cognitive decline in normal ageing: A review

Insulin-like Growth Factor 1 (IGF-1) and its signaling pathway play a primary role in normal growth and ageing, however serum IGF-1 is known to reduce with advancing age. Recent findings suggest IGF-1 is essential for neurogenesis in the adult brain, and this reduction of IGF-1 with ageing may contribute to age-related cognitive decline. Experimental studies have shown manipulation of the GH/GF-1 axis can slow rates of cognitive decline in animals, making IGF-1 a potential biomarker of cognition, and/or its signaling pathway a possible therapeutic target to prevent or slow age-related cognitive decline. A systematic literature review and qualitative narrative summary of current evidence for IGF-1 as a biomarker of cognitive decline in the ageing brain was undertaken. Results indicate IGF-1 concentrations do not confer additional diagnostic information for those with cognitive decline, and routine clinical measurement of IGF-1 is not currently justified. In cases of established cognitive impairment, it remains unclear whether increasing circulating or brain IGF-1 may reverse or slow down the rate of further decline. Advances in neuroimaging, genetics, neuroscience and the availability of large well characterized biobanks will facilitate research exploring the role of IGF-1 in both normal ageing and age-related cognitive decline.

Spatial learning and memory in male mice with altered growth hormone action

Growth hormone (GH) has a significant influence on cognitive performance in humans and other mammals. To understand the influence of altered GH action on cognition, we assessed spatial learning and memory using a Barnes maze (BM) comparing twelve-month old, male, bovine GH (bGH) and GH receptor antagonist (GHA) transgenic mice and their corresponding wild type (WT) littermates. During the acquisition training period in the BM, bGH mice showed increased latency, traveled longer path lengths and made more errors to reach the target than WT mice, indicating significantly poorer learning. Short-term memory (STM) and long-term memory (LTM) trials showed significantly suppressed memory retention in bGH mice when compared to the WT group. Conversely, GHA mice showed significantly better learning parameters (latency, path length and errors) and increased use of an efficient search strategy than WT mice. Our study indicates a negative impact of GH excess and a beneficial effect of the inhibition of GH action on spatial learning and memory and, therefore, cognitive performance in male mice. Further research to elucidate GH's role in brain function will facilitate identifying therapeutic applications of GH or GHA for neuropathological and neurodegenerative conditions.

IGF-1 has sexually dimorphic, pleiotropic, and time-dependent effects on healthspan, pathology, and lifespan

Reduced circulating levels of IGF-1 have been proposed as a conserved anti-aging mechanism that contributes to increased lifespan in diverse experimental models. However, IGF-1 has also been shown to be essential for normal development and the maintenance of tissue function late into the lifespan. These disparate findings suggest that IGF-1 may be a pleiotropic modulator of health and aging, as reductions in IGF-1 may be beneficial for one aspect of aging, but detrimental for another. We postulated that the effects of IGF-1 on tissue health and function in advanced age are dependent on the tissue, the sex of the animal, and the age at which IGF-1 is manipulated. In this study, we examined how alterations in IGF-1 levels at multiple stages of development and aging influence overall lifespan, healthspan, and pathology. Specifically, we investigated the effects of perinatal, post-pubertal, and late-adult onset IGF-1 deficiency using genetic and viral approaches in both male and female igf ^f/f C57Bl/6 mice. Our results support the concept that IGF-1 levels early during lifespan establish the conditions necessary for subsequent healthspan and pathological changes that contribute to aging. Nevertheless, these changes are specific for each sex and tissue. Importantly, late-life IGF-1 deficiency (a time point relevant for human studies) reduces cancer risk but does not increase lifespan. Overall, our results indicate that the levels of IGF-1 during development influence late-life pathology, suggesting that IGF-1 is a developmental driver of healthspan, pathology, and lifespan.

High Postnatal Growth Hormone Levels Are Related to Cognitive Deficits in a Group of Children Born Very Preterm

CONTEXT AND OBJECTIVES

Little is known regarding the influence of GH on brain development, especially in infants born very preterm (VP; <30 weeks' gestation). Preterm infants are thought to have higher levels of GH in the first days of life compared with full-term infants. VP infants experience cognitive difficulties in childhood and have a diffuse pattern of structural brain abnormalities. This study aimed to explore the relationship between postnatal GH concentrations following VP birth and its association with cognitive functioning and brain volumes at age 7 years.

METHODS

Eighty-three infants born VP had GH concentrations measured at eight time points postnatally, and 2- and 6-week area under the curve (AUC) summary measures were calculated. Followup at age 7 years included neuropsychological assessment and brain magnetic resonance imaging. Univariable and multivariable regression modeling were used where AUC for GH was the main predictor of neurodevelopmental outcome at age 7 years.

RESULTS

Univariable modeling revealed that higher GH levels (2-week AUC) were related to poorer performance on a verbal working memory (P = .04) and shifting attention task (P = .01). These relationships persisted on multivariable modeling and when the 6-week AUC was analyzed; working memory (P = .03), immediate spatial memory (P = .02), and delayed spatial memory (P = .03) deficits were found. Higher GH levels were also associated with larger amygdala volumes after adjustment for potential confounders (P = .002, 2-week AUC; P = .03, 6-week AUC).

CONCLUSIONS

Higher postnatal GH levels may potentially contribute to the documented neurodevelopmental abnormalities seen in children born VP at school age.

Metabolomic analysis reveals a unique urinary pattern in normozoospermic infertile men

Normozoospermic infertility has become a common and important health problem worldwide. We designed this metabolomic case-control study to investigate the possible mechanism and urinary biomarkers of normozoospermic infertility. Normozoospermic infertile cases (n = 71) and fertile controls (n = 47) were recruited. A urinary metabolome pattern could discriminate normozoospermic infertile cases from fertile controls. A total of 37 potential biomarkers were identified; these have functionally important roles in energy production, antioxidation, and hormone regulation in spermatogenesis. This gave rise to a combined biomarker pattern of leukotriene E4, 3-hydroxypalmitoylcarnitine, aspartate, xanthosine, and methoxytryptophan pointing to a diagnostic capability (AUC = 0.901, sensitivity = 85.7%, and specificity = 86.8%) in a ROC model; these markers may highlight keynote events of normozoospermic infertility. Stalled medium- and long-chain fatty acid metabolism with improved ketone body metabolism, plus decreased levels of malate and aspartate could result in citrate cycle alterations via a malate-aspartate shuttle in ATP generation in spermatogenesis. Inhibitory alterations in the normal hormone-secreting activity in spermatogenesis were suggested in normozoospermic infertility. Folate deficiency and oxidative stress may jointly impact infertile patients. The disruption of eicosanoid metabolism and xanthine oxidase system, which were tightly associated with energy metabolism and oxidative stress, was also a potential underlying mechanism. In addition, depression might be associated with normozoospermic infertility via neural activity-related metabolites. This study suggests that the urinary metabolome can be used to differentiate normozoospermic infertile men from fertile individuals. Potential metabolic biomarkers derived from these analyses might be used to diagnose what remains a somewhat idiopathic condition and provide functional insights into its pathogenesis.

Isolated growth hormone deficiency (GHD) in childhood and adolescence: recent advances

The diagnosis of GH deficiency (GHD) in childhood is a multistep process involving clinical history, examination with detailed auxology, biochemical testing, and pituitary imaging, with an increasing contribution from genetics in patients with congenital GHD. Our increasing understanding of the factors involved in the development of somatotropes and the dynamic function of the somatotrope network may explain, at least in part, the development and progression of childhood GHD in different age groups. With respect to the genetic etiology of isolated GHD (IGHD), mutations in known genes such as those encoding GH (GH1), GHRH receptor (GHRHR), or transcription factors involved in pituitary development, are identified in a relatively small percentage of patients suggesting the involvement of other, yet unidentified, factors. Genome-wide association studies point toward an increasing number of genes involved in the control of growth, but their role in the etiology of IGHD remains unknown. Despite the many years of research in the area of GHD, there are still controversies on the etiology, diagnosis, and management of IGHD in children. Recent data suggest that childhood IGHD may have a wider impact on the health and neurodevelopment of children, but it is yet unknown to what extent treatment with recombinant human GH can reverse this effect. Finally, the safety of recombinant human GH is currently the subject of much debate and research, and it is clear that long-term controlled studies are needed to clarify the consequences of childhood IGHD and the long-term safety of its treatment.

Growth hormone-releasing hormone effects on brain γ-aminobutyric acid levels in mild cognitive impairment and healthy aging

IMPORTANCE

Growth hormone-releasing hormone (GHRH) has been previously shown to have cognition-enhancing effects. The role of neurotransmitter changes, measured by proton magnetic resonance spectroscopy, may inform the mechanisms for this response.

OBJECTIVE

To examine the neurochemical effects of GHRH in a subset of participants from the parent trial.

DESIGN

Randomized, double-blind, placebo-controlled substudy of a larger trial.

SETTING

Clinical research unit at the University of Washington School of Medicine.

PARTICIPANTS

Thirty adults (17 with mild cognitive impairment [MCI]), ranging in age from 55 to 87 years, were enrolled and successfully completed the study.

INTERVENTIONS

Participants self-administered daily subcutaneous injections of tesamorelin (Theratechnologies Inc), a stabilized analogue of human GHRH (1 mg/d), or placebo 30 minutes before bedtime for 20 weeks. At baseline and weeks 10 and 20, participants underwent brain magnetic resonance imaging and spectroscopy protocols and cognitive testing and provided blood samples after fasting. Participants also underwent glucose tolerance tests before and after intervention.

MAIN OUTCOMES AND MEASURES

Brain levels of glutamate, inhibitory transmitters γ-aminobutyric acid (GABA) and N-acetylaspartylglutamate (NAAG), and myo-inositol (MI), an osmolyte linked to Alzheimer disease in humans, were measured in three 2 × 2 × 2-cm3 left-sided brain regions (dorsolateral frontal, posterior cingulate, and posterior parietal). Glutamate, GABA, and MI levels were expressed as ratios to creatine plus phosphocreatine, and NAAG was expressed as a ratio to N-acetylaspartate.

RESULTS

After 20 weeks of GHRH administration, GABA levels were increased in all brain regions (P < .04), NAAG levels were increased (P = .03) in the dorsolateral frontal cortex, and MI levels were decreased in the posterior cingulate (P = .002). These effects were similar in adults with MCI and older adults with normal cognitive function. No changes in the brain levels of glutamate were observed. In the posterior cingulate, treatment-related changes in serum insulin-like growth factor 1 were positively correlated with changes in GABA (r = 0.47; P = .001) and tended to be negatively correlated with MI (r = -0.34; P = .06). Consistent with the results of the parent trial, a favorable treatment effect on cognition was observed in substudy participants (P = .03). No significant associations were observed between treatment-related changes in neurochemical and cognitive outcomes. Glucose homeostasis in the periphery was not reliably affected by GHRH administration and did not account for treatment neurochemical effects.

CONCLUSIONS

Twenty weeks of GHRH administration increased GABA levels in all 3 brain regions, increased NAAG levels in the frontal cortex, and decreased MI levels in the posterior cingulate. To our knowledge, this is the first evidence that 20 weeks of somatotropic supplementation modulates inhibitory neurotransmitter and brain metabolite levels in a clinical trial, and it provides preliminary support for one possible mechanism to explain favorable GHRH effects on cognition in adults with MCI and in healthy older adults. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00257712.

Aging, synaptic dysfunction, and insulin-like growth factor (IGF)-1

Insulin-like growth factor (IGF)-1 is an important neurotrophic hormone. Deficiency of this hormone has been reported to influence the genesis of cognitive impairment and dementia in the elderly patients. Nevertheless, there are studies indicating that cognitive function can be maintained into old age even in the absence of circulating IGF-1 and studies that link IGF-1 to an acceleration of neurological diseases. Although IGF-1 has a complex role in brain function, synaptic effects appear to be central to the IGF-1-induced improvement in learning and memory. In this review, synaptic mechanisms of learning and memory and the effects of IGF-1 on synaptic communication are discussed. The emerging data indicate that synaptic function decreases with age and that IGF-1 contributes to information processing in the brain. Further studies that detail the specific actions of this important neurotrophic hormone will likely lead to therapies that result in improved cognitive function for the elderly patients.

Reduced growth hormone secretion after cranial irradiation contributes to neurocognitive dysfunction

The objective of this study was to investigate the relation between growth hormone (GH) and attentional electro-cortical responses to task-relevant stimuli (N2b), target detections, speed of responding, P300 latencies, and performance on neuropsychological tests in 19 patients who received external beam radiation therapy for brain tumors in adulthood. In addition, we studied the association between IGF-I and activation of the motor cortex responses (lateralized readiness potential, LRP). Brain function was assessed using event-related potentials (ERPs) during a go/no go selective-attention task, including N2b, P300 and selective motor preparation as reflected in the LRP. Correlations were calculated between peak GH levels after a standardized growth hormone-releasing hormone (GHRH)-arginine test, plasma IGF-I, and cognitive functions. We separately studied four patients who were diagnosed with GHD according to the GHRH-arginine test. Performance on WAIS digit span backward and the Rey-Osterrieth complex figure test correlated positively with GH peak. GHD patients performed worse than non-GHD patients on Stroop interference, trail making B/A attentional shifting and Rey-Osterrieth complex figure test. At trend-level significance, trails A performance was better in patients with lower GH levels and higher radiation doses, and GHD participants detected fewer targets in the go/no go selective attention task. N2b was not significantly altered by GH status. Furthermore, plasma IGF-I was positively correlated with the sum of digit span forward and backward. No relations with P300 were observed. In this study only 21% (4/19) of the patients who received fractionated radiotherapy for a non-endocrine brain tumor were diagnosed with GHD. GHD in these patients was associated with impaired interference control, attentional shifting, and visual long-term memory. The results for interference control and attentional shifting suggest an additional effect of the radiation history.

Genetic and environmental contributions to the association between anthropometric measures and iq: a study of Minnesota twins at age 11 and 17

Associations of height and head circumference with IQ are well documented, but much less is known about the association of IQ with other anthropometric measures or the mechanisms behind these associations. We therefore analyzed the associations between IQ and several anthropometric measures using a twin-study design. Twins born in Minnesota were assessed at either age 11 (756 complete pairs) or 17 (626 complete pairs) and analyzed using genetic modeling. Head circumference and height showed the most consistent positive associations with IQ, whereas more detailed anthropometric measures were not significantly better predictors of IQ. These associations were mainly due to common genetic factors. Our results suggest that the same genetic factors have an effect on physical and cognitive development. Head circumference and height capture information on children's physical development, which is partly associated also with cognitive development.

Circulating IGF1 regulates hippocampal IGF1 levels and brain gene expression during adolescence

GH and its anabolic mediator, IGF1, are important not only in somatic growth but also in the regulation of brain function. Even though GH treatment has been used clinically to improve body composition and exercise capacity in adults, its influence on central nervous system function has only recently been recognized. This is also the case for children with childhood-onset GH deficiency (GHD) where GH has been used to stimulate bone growth and enhance final adult height. Circulating IGF1 is transported across the blood-brain barrier and IGF1 and its receptors are also synthesized in the brain by neurons and glial and endothelial cells. Nevertheless, the relationship between circulating IGF1 and brain IGF1 remains unclear. This study, using a GH-deficient dwarf rat model and peripheral GH replacement, investigated the effects of circulating IGF1 during adolescence on IGF1 levels in the brain. Our results demonstrated that hippocampal IGF1 protein concentrations during adolescence are highly regulated by circulating IGF1, which were reduced by GHD and restored by systematic GH replacement. Importantly, IGF1 levels in the cerebrospinal fluid were decreased by GHD but not restored by GH replacement. Furthermore, analysis of gene expression using microarrays and RT-PCR indicated that circulating IGF1 levels did not modify the transcription of Igf1 or its receptor in the hippocampus but did regulate genes that are involved in microvascular structure and function, brain development, and synaptic plasticity, which potentially support brain structures involved in cognitive function during this important developmental period.

Effect of growth hormone replacement therapy on cognition after traumatic brain injury

Traumatic brain injury (TBI) is a major public health issue, and yet medical science has little to offer for the persistent symptoms that prevent many of these individuals from fully re-entering society. Post-traumatic hypopituitarism, and specifically growth hormone deficiency (GHD), has been found in a large percentage of individuals with chronic moderate to severe TBI. Presently, there are no published treatment studies of hormone replacement in this population. In this study, 83 subjects with chronic TBI were screened for hypopituitarism. Forty-two subjects were found to have either GHD or GH insufficiency (GHI), of which 23 agreed to be randomized to either a year of GH replacement or placebo. All subjects completed the study with no untoward side effects from treatment. A battery of neuropsychological tests and functional measures were administered before and after treatment. Improvement was seen on the following tests: Dominant Hand Finger Tapping Test, Wechsler Adult Intelligence Scale III-Information Processing Speed Index, California Verbal Learning Test II, and the Wisconsin Card Sorting Test (executive functioning). The findings of this pilot study provide preliminary evidence suggesting that some of the cognitive impairments observed in persons who are GHD/GHI after TBI may be partially reversible with appropriate GH replacement therapy.

On the sources of the height-intelligence correlation: new insights from a bivariate ACE model with assortative mating

A robust positive correlation between height and intelligence, as measured by IQ tests, has been established in the literature. This paper makes several contributions toward establishing the causes of this association. First, we extend the standard bivariate ACE model to account for assortative mating. The more general theoretical framework provides several key insights, including formulas to decompose a cross-trait genetic correlation into components attributable to assortative mating and pleiotropy and to decompose a cross-trait within-family correlation. Second, we use a large dataset of male twins drawn from Swedish conscription records and examine how well genetic and environmental factors explain the association between (i) height and intelligence and (ii) height and military aptitude, a professional psychologist's assessment of a conscript's ability to deal with wartime stress. For both traits, we find suggestive evidence of a shared genetic architecture with height, but we demonstrate that point estimates are very sensitive to assumed degrees of assortative mating. Third, we report a significant within-family correlation between height and intelligence (p^ = 0.10), suggesting that pleiotropy might be at play.

Growth hormone and selective attention: a review

INTRODUCTION

The relation between growth hormone (GH) secretion and general cognitive function has been established. General cognitive functioning depends on core functions including selective attention, which have not been addressed specifically in relation to GH. The present review addresses current insights about specific effects of growth hormone deficiency (GHD) on varieties of selective attention, as well as effects of GH suppletion.

MATERIALS AND METHODS

Studies investigating relationships between GH status and valid measures of selective or divided attention were reviewed.

RESULTS AND DISCUSSION

There are no indications that GHD is characterized by impaired attribute selection, interference control, or attentional switching. In contrast, a few studies point to a deficit in integrated processing of multiple dimensions, as well as speed of information processing. There is also weak evidence for beneficial effects of GH replacement in the opposite direction in these domains.

CONCLUSIONS

The function of integrated processing of multiple stimulus dimensions may be based on neural mechanisms in the anterior cingulate cortex and its extensive connections to the hippocampus, the latter being known to be rich in GH receptors.

Early-onset GH deficiency results in spatial memory impairment in mid-life and is prevented by GH supplementation

GH levels increase to high concentrations immediately before puberty then progressively decline with age. GH deficiency (GHD) originating in childhood is treated with GH supplementation to foster somatic development during adolescence. It is not clear if or how early GH replacement affects memory in adulthood, or whether it can prevent the cognitive deficits commonly observed in adults with childhood-onset GHD. Rats homozygous for the Dw-4 mutation (dwarf) do not exhibit the normal increase in GH at 4 weeks of age when GH levels normally rise and are used to model childhood or early-onset GHD (EOGHD). One group of these rats was injected with GH from 4 to 14 weeks of age to model GH supplementation during adolescence with GHD beginning in adulthood (adult-onset GHD; AOGHD). Another group received GH from 4 weeks throughout the lifespan to model normal lifespan GH (GH-replete). Age-matched, Dw-4 heterozygous rats (HZ) do not express the dwarf phenotype and were used as controls. At 8 and 18 months of age, spatial learning in the water maze was assessed. At 8 months of age all experimental groups were equally proficient. However, at 18 months of age, the EOGHD group had poor spatial learning compared to the AOGHD, GH-replete, and HZ groups. Our data indicate that GHD during adolescence has negative effects on learning and memory that emerge by middle-age unless prevented by GH supplementation.

Circulating insulin-like growth factor I and cognitive function: neuromodulation throughout the lifespan

Insulin-like growth factor I (IGF-I) is central to the somatotropic (growth hormone) axis. It promotes tissue growth and continues to have anabolic effects in adulthood. Accumulating evidence from the last decade, however, reveals that circulating levels of IGF-I also significantly affects cognitive brain function. Specifically, the decline of serum IGF-I might be associated with the age-related cognitive decline in elderly people. Moreover, psychiatric and neurological conditions characterized by cognitive impairment may be characterized by altered levels of IGF-I. Some evidence is emerging that interventions that target the GH/IGF-I axis may improve cognitive functioning, at least in deficient states. As there is evidence linking high serum IGF-I levels with cancer risk, these interventions should be carefully evaluated. On a cellular and molecular level, IGF-I may be a crucial component of neural homeostasis since disturbed IGF-I input is inevitably linked to perturbed function. Consistent with this, all nerve cells are potential targets of IGF-I actions, including neurons, glia, endothelial, epithelial, and perivascular cells. Indeed, many key cellular processes in the brain are affected by IGF-I's neurotrophic and modulatory actions. We review the regulation by IGF-I of neurotransmission and neuronal plasticity and conclude that serum IGF-I is an important mediator of neuronal growth, survival and function throughout the lifespan. The role of IGF-I in synaptic plasticity render its neurotrophic potential a key target for remediating the cognitive impairment associated with a range of neurological conditions.

Cognition in the adult with childhood-onset GH deficiency

The GH/IGF1 axis may play an important role in cognitive function. This theory is supported by the finding that both GH and IGF1 receptors are located in several brain areas such as the hippocampus, a brain area that is known to play an essential role in cognitive processes, especially memory and learning. However, the exact mechanism by which the GH/IGF1 axis influences the cognitive functions is still unknown. Furthermore, little is known about the cognition in adults with both childhood-onset and adult-onset GH deficiency (CO-GHD and AO-GHD). Recent data indicate that cognitive function, particularly attention and memory, in adults with GHD might be impaired. To date, only a limited number of studies have been conducted to study the effects of GH replacement therapy on cognitive function in adults with GHD. In this paper, the results of studies on cognitive functioning in GHD patients, in particular the results of the studies performed in adults with CO-GHD, and the effects of GH replacement therapy in these patients, will be discussed.

Plasma growth hormones, P300 event-related potential and test of variables of attention (TOVA) are important neuroendocrinological predictors of early cognitive decline in a clinical setting: evidence supported by structural equation modeling (SEM) parameter estimates

A review of the literature in both animals and humans reveals that changes in sex hormone have often been associated with changes in behavioral and mental abilities. Previously published research from our laboratory, and others, provides strong evidence that P300 (latency) event-related potential (ERP), a marker of neuronal processing speed, is an accurate predictor of early memory impairment in both males and females across a wide age range. It is our hypothesis, given the vast literature on the subject, that coupling growth hormones (insulin-like growth factor-I, (IGF-I) and insulin-like growth factor binding protein 3 (IGF-BP3)), P300 event-related potential and test of variables of attention (TOVA) are important neuroendocrinological predictors of early cognitive decline in a clinical setting. To support this hypothesis, we utilized structural equation modeling (SEM) parameter estimates to determine the relationship between aging and memory, as mediated by growth hormone (GH) levels (indirectly measured through the insulin-like growth factor system), P300 latency and TOVA, putative neurocognitive predictors tested in this study. An SEM was developed hypothesizing a causal directive path, leading from age to memory, mediated by IGF-1 and IGF-BP3, P300 latency (speed), and TOVA decrements. An increase in age was accompanied by a decrease in IGF-1 and IGF-BP3, an increase in P300 latency, a prolongation in TOVA response time, and a decrease in memory functioning. Moreover, independent of age, decreases in IGF-1 and IGF-BP3, were accompanied by increases in P300 latency, and were accompanied by increases in TOVA response time. Finally, increases in P300 latency were accompanied by decreased memory function, both directly and indirectly through mediation of TOVA response time. In summary, this is the first report utilizing SEM to reveal the finding that aging affects memory function negatively through mediation of decreased IGF-1 and IGF-BP3, and increased P300 latency (delayed attention and processing speed).

Genetic contributions to the association between height and intelligence: Evidence from Dutch twin data from childhood to middle age

A positive association between intelligence (IQ) and height has been reported previously. It is generally assumed that this association reflects the effect of childhood environment on IQ, but there is still little research supporting directly this hypothesis. We studied the association between height and IQ in 209 Dutch twin pairs at the ages of 5, 7, 10 and 12 years, 208 twin pairs at 16 and 18 years of age and 567 twin pairs and their siblings in adulthood. The heritability of height was high in all cohorts and across all ages (a2 = 0.93 - 0.96). In adulthood, heritability was also high for full-scale IQ (FSIQ: a2 = 0.83-0.84) and somewhat lower for verbal IQ (VIQ: a2 = 0.66-0.84). In early childhood, the heritability was lower, and common environmental factors had a substantial effect on FSIQ and VIQ. A positive association of height and IQ was found in early childhood and adolescence. In adulthood, a correlation was found between height and FSIQ in young adulthood and between height and VIQ in middle age. All correlations could be ascribed to genetic factors influencing both height and IQ. Thus, these results show that the association between height and IQ should not be directly regarded as evidence for childhood living conditions affecting IQ, but the effect of genetic factors affecting independently or interacting with environmental factors should be considered as well.

The effects of growth hormone (GH) deficiency and GH replacement on cognitive performance in adults: a meta-analysis of the current literature

OBJECTIVE

There is growing evidence in the neuropsychological literature that growth hormone (GH) deficiency is associated with cognitive impairment. There is also evidence that this impairment may be ameliorated with GH replacement therapy. The current study assessed the nature and severity of cognitive impairment associated with growth hormone deficiency, as well as effect of GH replacement on cognitive function by conducting a meta-analysis of the published literature to date.

METHOD

Thirteen studies met the inclusion criteria and these included: five cross-sectional studies investigating GH deficiency; and, eight (eight prospective, two of which also included cross-sectional comparisons) investigating GH replacement. Effect sizes (Cohen's d) falling into six cognitive domains were computed (separately for GH deficiency and GH replacement).

RESULTS

For GH deficiency, each of the cognitive domains assessed (besides language) showed moderate to large impairments when compared to matched controls (Effect sizes -0.46 to -1.46). For GH replacement, even though treated patients still performed moderately to largely below that of controls, when compared to their own baselines (as in prospective analyses), moderate improvements were found in cognitive performance, particularly attention and memory.

CONCLUSION

This meta-analysis clearly demonstrates the link between GH and cognitive performance, where poor performance can be ameliorated with GH treatment.

Neurocognitive function in adults with growth hormone deficiency

The clinical condition of growth hormone deficiency (GHD) as a consequence of pituitary or hypothalamic disease has been associated with reduced cognitive performance. In several studies, neuropsychological assessment has been performed in adults with GHD both before and after growth hormone (GH) replacement therapy. Interpretation of the available data is complicated by the variation in patient selection as well as the neuropsychological tests used in such studies. Most of the available studies indicate that GHD can lead to small, but clinically relevant changes in memory, processing speed and attention. Some of these changes may be reversed by GH replacement, although the number of reliable intervention studies is limited. In addition to the possible clinical relevance of neuropsychological improvement following GH replacement in patients with GHD, the observed findings may be of interest for studies in neurocognitive performance in other conditions associated with changes in the activity of the somatotrophic axis, and in the understanding of underlying pathophysiological mechanisms.

Cognitive function in growth hormone deficiency and growth hormone replacement

There is converging evidence from neuropsychological studies that growth hormone (GH) is associated with cognitive function. The aim of the current study was to review the existing neuropsychological literature for studies in which cognitive assessment had been conducted in patients with GH deficiency (GHD), and where change in cognitive function had been assessed following treatment with GH. Studies that have investigated relationships between GH and cognitive function and those that have developed methodological and statistical approaches that could be useful in future GH studies were identified. In this review, GH levels were found to be associated with cognitive function. Untreated individuals with GHD showed reliable impairment in memory and attentional functions when compared with matched controls. Appropriately designed prospective studies also indicated that cognitive function improved with GH treatment. It was concluded that individuals with GHD do show cognitive impairment and that this is ameliorated to some extent by GH treatment. It is now important to establish the clinical importance of these findings, and further work is required to understand better the nature, magnitude and meaning of GH-related cognitive impairments and improvements.

Somatropin Therapy and Cognitive Function in Adults with Growth Hormone Deficiency

Both growth hormone (GH) and insulin-like growth factor (IGF)-I have receptors in the brain, in particular in areas that are involved in cognitive function. Therefore, it has been hypothesized that GH deficiency can lead to cognitive dysfunction, and that somatropin replacement therapy may have beneficial effects on cognitive function in GH-deficient patients. In this review, an overview is given regarding the possible effects of decreased activity of the GH/IGF-I axis and somatropin therapy in GH deficiency in relation to cognitive function. The available data regarding cognitive function in GH-deficient patients are limited, but suggest that this condition can lead to specific cognitive changes, in particular attentional deficits and altered processing speed. The underlying mechanisms and the effects of somatropin treatment on cognitive function in GH deficiency are still unclear. Similar studies to those performed in patients with GH deficiency have been performed regarding the cognitive changes in elderly patients with relatively low GH and/or IGF-I levels. Large controlled studies regarding the effects and safety of somatropin treatment in healthy elderly patients have not been performed.

Effects of growth hormone substitution therapy on cognitive functioning in growth hormone deficient patients: a functional MRI study

Patients with childhood-onset growth hormone (GH) deficiency (GHD) show impairments in mood and cognitive functioning which may resolve following GH substitution. Brain functional magnetic resonance imaging (fMRI) during performance of a memory task was used to assess the cerebral activity of such patients. Thirteen childhood-onset GHD patients (mean age 27.3 +/- 6.9 years) were included in a double-blind, placebo-controlled study. The effects of 6 months of GH replacement or placebo therapy were studied using neuropsychological tests and fMRI. One patient was excluded from the study due to noncompliance with the protocol. Six months of GH substitution in these GHD patients resulted in improved memory functioning, both for long-term and working memory. fMRI showed activations during the working memory task in prefrontal, parietal, motor, and occipital cortices, as well as in the right thalamus and anterior cingulate cortex. Decreased activation in the ventrolateral prefrontal cortex was observed after GH treatment as compared with placebo treatment, indicating decreased effort and more efficient recruitment of the neural system involved. It can be concluded that GH treatment for 6 months improved the long-term as well as the working memory in patients with GHD, and this was associated with decreased brain activation in the ventrolateral prefrontal cortex. GH substitution in GHD patients is beneficial for cognitive functioning, the effects of which can be visualized by means of neuroimaging.

Growth hormone deficiency and memory functioning in adults visualized by functional magnetic resonance imaging

Cognitive functioning, especially memory performance, is known to be impaired in patients with childhood-onset growth hormone deficiency (CO-GHD), and growth hormone substitution has been found to counteract this memory impairment. Neuropsychological and functional magnetic resonance imagining (fMRI) data acquired during a working memory task in 13 childhood-onset GH-deficient patients were compared with 13 age, sex and education level matched healthy controls. Results demonstrated that there is no difference in the quality of the performance in the working memory task between GH-deficient patients and control subjects. However, memory speed was found to be subnormal in patients. Concerning mood, patients reported more complaints of fatigue, and less vigor. Imaging data showed that patients had increased activity in dorsolateral/ventrolateral prefrontal cortex, anterior cingulate cortex, parietal cortex, supplementary motor and motor cortex, as well as in the thalamus and precuneus area. Increasing task load was also associated with an increase in brain activity in similar areas in patients compared to control subjects. In conclusion, this fMRI study shows that GH-deficient patients have a subnormal memory speed, but no impaired quality of memory performance, which may be due to compensatory recruitment of dorsal prefrontal brain regions. These findings indicate that the GH-IGF-1 axis contributes to prefrontal functioning in patients with CO-GHD.