Model informed quantification of the feed-forward stimulation of growth hormone by growth hormone-releasing hormone

Aims: Growth hormone (GH) secretion is pulsatile and secretion varies highly between individuals. To understand and ultimately predict GH secretion, it is important to first delineate and quantify the interaction and variability in the biological processes underlying stimulated GH secretion. This study reports on the development of a population nonlinear mixed effects model for GH stimulation, incorporating individual GH kinetics and the stimulation of GH by GH-releasing hormone (GHRH). Methods: Literature data on the systemic circulation, the median eminence, and the anterior pituitary were included as system parameters in the model. Population parameters were estimated on data from 8 healthy normal weight and 16 obese women who received a 33 μg recombinant human GH dose. The next day, a bolus injection of 100 μg GHRH was given to stimulate GH secretion. Results: The GH kinetics were best described with the addition of 2 distribution compartments with a bodyweight dependent clearance (increasing linearly from 24.7 L/h for a 60-kg subject to 32.1 L/h for a 100-kg subject). The model described the data adequately with high parameter precision and significant interindividual variability on the GH clearance and distribution volume. Additionally, high variability in the amount of secreted GH, driven by GHRH receptor activation, was identified (coefficient of variation = 90%). Conclusion: The stimulation of GH by GHRH was quantified and significant interindividual variability was identified on multiple parameters. This model sets the stage for further development of by inclusion of additional physiological components to quantify GH secretion in humans

Severe tracheal and bronchial collapse in adults with type II mucopolysaccharidosis

Background: Mucopolysaccharidosis type II (MPSII) patients frequently suffer from dyspnoea caused by restrictive airway disease due to skeletal abnormalities as well as glycosaminoglycans (GAG) accumulation at different levels of the airway, including the trachea. In this study we describe the extent of the tracheal and bronchial narrowing, the changes in airway diameter during respiration and the effects of these obstructions on respiratory function in adult MPSII patients. Methods: Five adult MPSII patients (mean age 40 years) were included. Pulmonary function tests and in- and expiratory chest CT scans were obtained. Cross-sectional areas of trachea and main bronchi were measured at end-inspiration and -expiration and percentage collapse was calculated. Results: There was diffuse narrowing of the entire intra-thoracic trachea and main bronchi and severe expiratory collapse of the trachea in all patients. At 1 cm above the aortic arch the median % collapse of the trachea was 68 (range 60 to 77 %), at the level of the aortic arch 64 (range 21-93 %), for the main bronchi this was 58 (range 26-66 %) on the left and 44 (range 9-76 %) on the right side. The pulmonary function tests showed that this airway collapse results in obstructive airway disease in all patients, which was severe (forced expiratory volume <50 % of predicted) in four out of five patients. Conclusion: In adult MPS II patients, central airways diameters are strikingly reduced and upon expiration there is extensive collapse of the trachea and main bronchi. This central airways obstruction explains the severe respiratory symptoms in MPSII patients

Neurocognitive outcome and mental health in children with tyrosinemia type 1 and phenylketonuria: A comparison between two genetic disorders affecting the same metabolic pathway

Tyrosinemia type 1 (TT1) and phenylketonuria (PKU) are both inborn errors of phenylalanine–tyrosine metabolism. Neurocognitive and behavioral outcomes have always featured in PKU research but received less attention in TT1 research. This study aimed to investigate and compare neurocognitive, behavioral, and social outcomes of treated TT1 and PKU patients. We included 33 TT1 patients (mean age 11.24 years; 16 male), 31 PKU patients (mean age 10.84; 14 male), and 58 age- and gender-matched healthy controls (mean age 10.82 years; 29 male). IQ (Wechsler-subtests), executive functioning (the Behavioral Rating Inventory of Executive Functioning), mental health (the Achenbach-scales), and social functioning (the Social Skills Rating System) were assessed. Results of TT1 patients, PKU patients, and healthy controls were compared using Kruskal–Wallis tests with post-hoc Mann–Whitney U tests. TT1 patients showed a lower IQ and poorer executive functioning, mental health, and social functioning compared to healthy controls and PKU patients. PKU patients did not differ from healthy controls regarding these outcome measures. Relatively poor outcomes for TT1 patients were particularly evident for verbal IQ, BRIEF dimensions “working memory”, “plan and organize” and “monitor”, ASEBA dimensions “social problems” and “attention problems”, and for the SSRS “assertiveness” scale (all p values <0.001). To conclude, TT1 patients showed cognitive impairments on all domains studied, and appeared to be significantly more affected than PKU patients. More attention should be paid to investigating and monitoring neurocognitive outcome in TT1 and research should focus on explaining the underlying pathophysiological mechanism

New insights in the neurological phenotype of aceruloplasminemia in Caucasian patients.

INTRODUCTION: The diagnosis aceruloplasminemia is usually made in patients with advanced neurological manifestations of the disease. In these patients prognosis is poor, disabilities are severe and patients often die young. The aim of our study was to facilitate recognition of aceruloplasminemia at a disease stage at which treatment can positively influence outcome. Currently, the neurological phenotype of aceruloplasminemia has been mainly described in Japanese patients. This 'classical' phenotype consists of cerebellar ataxia, hyperkinetic movement disorders and cognitive decline. In this study we describe the spectrum of neurological disease in Caucasian patients. METHODS: Data on neurological presentation and follow-up were gathered from both our patients, homozygous for the G631R mutation in the CP gene, and other published Caucasian cases. Neurological features of aceruloplasminemia in Caucasian patients were compared to those summarized in Japanese patients. RESULTS: 21 Caucasian patients, both ours and the described cases, displayed a wide range of movement disorders with predominant chorea, parkinsonism and ataxia, and also tremor and dystonia. In addition to cognitive decline, nearly half of the Caucasian patients presented with psychiatric changes, including depression, anxiety and behavioral changes. In one-third of the neurologically symptomatic Caucasian patients, cognitive- or psychiatric changes were the first neurological manifestations of aceruloplasminemia. CONCLUSIONS: Aceruloplasminemia in Caucasian patients can present with a wider range and a different order of neurological symptoms than previously described in Japanese patients. Psychiatric changes and parkinsonism can be added to the spectrum of neurological disease. Cognitive- or psychiatric changes may be the first neurological manifestations of aceruloplasminemia