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      Future Directions: Growth Prediction Models

      a , b

      Hormone Research in Paediatrics

      S. Karger AG

      Prediction model, Growth hormone

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          Abstract

          Background: One strategy for optimizing growth hormone (GH) treatment is to develop mathematical models based on clinical data from the large numbers of subjects in the KIGS (Pfizer International Growth Study Database) and to compare the observed versus predicted growth responses in subjects with short stature secondary to idiopathic GH deficiency (GHD), Turner syndrome, small birth size and idiopathic causes of short stature. Mathematical Models: Variables employed in derived regression equations include those related to birth status, genetic potential, current clinical status, laboratory data and GH treatment schedule. These models can provide an accurate estimate of potential growth on GH therapy and the tools to optimize and individualize GH therapy to obtain maximum height with the least risk and the lowest cost. Current prediction models explain around 58% of GH responsiveness in subjects with GHD, 46% in subjects with Turner syndrome and 52% in those born small for gestational age. Future Considerations: The predictive value of these models could be improved by the inclusion of extended anthropometric variables and biological parameters such as insulin-like growth factor I levels. However, recent reports that common polymorphisms of theGH receptor (GHR) gene may be associated with variations in response to GH suggest that, in the future, molecular genetics may provide an additional tool for refining growth prediction models. This possibility is being explored in a pilot study examining the effects of candidate genes in a targeted KIGS population to determine whether the GHR geneor other gene variants contribute to growth response over the first year of GH treatment.

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          Most cited references 15

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          Dominant and recessive inheritance of morbid obesity associated with melanocortin 4 receptor deficiency.

          Over 20 severely obese subjects in 11 independent kindreds have been reported to have pathogenic heterozygous mutations in the gene encoding the melanocortin 4 receptor (MC4R), making this the most common known monogenic cause of human obesity. To date, the detailed clinical phenotype of this dominantly inherited disorder has not been defined, and no homozygous subjects have been described. We determined the nucleotide sequence of the entire coding region of the MC4R gene in 243 subjects with severe, early-onset obesity. A novel two-base pair GT insertion in codon 279 was found in two unrelated subjects, and four novel missense mutations, N62S, R165Q, V253I, C271Y, and one mutation (T112M) reported previously were found in five subjects. N62S was found in homozygous form in five children with severe obesity from a consanguineous pedigree. All four heterozygous carriers were nonobese. Several features of the phenotype, e.g. hyperphagia, tendency toward tall stature, hyperinsulinemia, and preserved reproductive function, closely resemble those reported previously in Mc4r knock-out mice. In addition, a marked increase in bone mineral density was seen in all affected subjects. In transient transfection assays, the N62S mutant receptor showed a responsiveness to alphaMSH that was intermediate between the wild-type receptor and mutant receptors carrying nonsense and missense mutations associated with dominantly inherited obesity. Thus MC4R mutations result in a syndrome of hyperphagic obesity in humans that can present with either dominant or recessive patterns of inheritance.
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            Prediction of response to growth hormone treatment in short children born small for gestational age: analysis of data from KIGS (Pharmacia International Growth Database).

            A model was developed that allows physicians to individualize GH treatment in children born short for gestational age (SGA) who fail to show spontaneous catch-up growth. Data from children (n = 613) in a large pharmacoepidemiological survey, the KIGS (Pharmacia International Growth Database), or who had participated in clinical trials were used to develop the model. Another group of similar children (n = 68) from KIGS was used for validation. In the first year of GH treatment, the growth response correlated positively with GH dose, weight at the start of GH treatment, and midparental height SD score and negatively with age at treatment start. Using this model, 52% of the variability of the growth response could be explained, with a mean error SD of 1.3 cm. GH dose was the most important response predictor (35% of variability), followed by age at treatment start. The second year growth response was best predicted by a three-parameter model (height velocity in yr 1 of treatment, age at start of treatment, and GH dose), which accounted for 34% of the variability, with an error SD of 1.1 cm. The first year response to GH treatment was the most important predictor of the second year response, accounting for 29% of the variability. No statistically significant differences between the predicted and observed growth responses were found when the models were applied to the validation groups. In conclusion, using simple variables, we have developed a model that can be used in clinical practice to adjust the GH dose to achieve the desired growth response in patients born SGA. Furthermore, this model can be used to provide patients with a realistic expectation of treatment and may help to identify compliance problems or other underlying causes of treatment failure.
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              A common polymorphism of the growth hormone receptor is associated with increased responsiveness to growth hormone.

              Growth hormone is used to increase height in short children who are not deficient in growth hormone, but its efficacy varies largely across individuals. The genetic factors responsible for this variation are entirely unknown. In two cohorts of short children treated with growth hormone, we found that an isoform of the growth hormone receptor gene that lacks exon 3 (d3-GHR) was associated with 1.7 to 2 times more growth acceleration induced by growth hormone than the full-length isoform (P < 0.0001). In transfection experiments, the transduction of growth hormone signaling through d3-GHR homo- or heterodimers was approximately 30% higher than through full-length GHR homodimers (P < 0.0001). One-half of Europeans are hetero- or homozygous with respect to the allele encoding the d3-GHR isoform, which is dominant over the full-length isoform. These observations suggest that the polymorphism in exon 3 of GHR is important in growth hormone pharmacogenetics.
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                Author and article information

                Journal
                HRE
                Horm Res Paediatr
                10.1159/issn.1663-2818
                Hormone Research in Paediatrics
                S. Karger AG
                978-3-8055-8475-3
                978-3-8055-8476-0
                1663-2818
                1663-2826
                2007
                December 2007
                10 December 2007
                : 68
                : Suppl 5
                : 51-56
                Affiliations
                aSaban Research Institute, Childrens Hospital Los Angeles, Los Angeles, Calif., USA; bUniversity of Cambridge, Department of Paediatrics, Addenbrooke’s Hospital, Cambridge, UK
                Article
                110476 Horm Res 2007;68:51–56
                10.1159/000110476
                18174708
                © 2007 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 1, Tables: 2, References: 22, Pages: 6
                Categories
                KIGS Highlight Session

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