Obesity due to melanocortin 4 receptor (MC4R) deficiency is associated with increased linear growth and final height, fasting hyperinsulinemia, and incompletely suppressed growth hormone secretion.
BACKGROUND
Melanocortin receptor 4 (MC4R) deficiency is characterized by increased linear growth greater than expected for the degree of obesity.


OBJECTIVE
The objective of the investigation was to study the somatotroph axis in obese MC4R-deficient patients and equally obese controls.


METHODS
We obtained anthropometric measurements and insulin concentrations in 153 MC4R-deficient subjects and 1392 controls matched for age and severity of obesity. We measured fasting IGF-I, IGF-II, IGF binding protein (IGFBP)-1, IGFBP-3, and acid-labile subunit levels in a subset of 33 MC4R-deficient patients and 36 control subjects. We examined pulsatile GH secretion in six adult MC4R-deficient subjects and six obese controls.


RESULTS
Height sd score was significantly greater in MC4R-deficient children under 5 yr of age compared with controls (mean ± SEM: 2.3 ± 0.06 vs. 1.8 ± 0.04, P < 0.001), an effect that persisted throughout childhood. Final height (cm) was greater in MC4R-deficient men (mean ± SEM 173 ± 2.5 vs. 168 ± 2.1, P < 0.001) and women (mean 165 ± 2.1 vs. 158 ± 1.9, P < 0.001). Fasting IGF-I, IGF-II, acid-labile subunit, and IGFBP-3 concentrations were similar in the two groups. GH levels were markedly suppressed in obese controls, but pulsatile GH secretion was retained in MC4R deficiency. The mean maximal GH secretion rate per burst (P < 0.05) and mass per burst (P < 0.05) were increased in MC4R deficiency, consistent with increased pulsatile and total GH secretion. Fasting insulin levels were markedly elevated in MC4R-deficient children.


CONCLUSIONS
In MC4R deficiency, increased linear growth in childhood leads to increased adult final height, greater than predicted by obesity alone. GH pulsatility is maintained in MC4R deficiency, a finding consistent with animal studies, suggesting a role for MC4R in controlling hypothalamic somatostatinergic tone. Fasting insulin levels are significantly higher in children carrying MC4R mutations. Both of these factors may contribute to the accelerated growth phenotype characteristic of MC4R deficiency.
Department of Pediatrics, Hospital das Clínicas, University of Sao Paulo, Ribeirão Preto, Sao Paulo, Brazil.
Carlos E
CE
Martinelli
Julia M
JM
Keogh
Jerry R
JR
Greenfield
Elana
E
Henning
Agatha A
AA
van der Klaauw
Anthea
A
Blackwood
Stephen
S
O'Rahilly
Ferdinand
F
Roelfsema
Cecilia
C
Camacho-Hübner
Hanno
H
Pijl
I Sadaf
IS
Farooqi
D000886:Anthropometry; D001827:Body Height / Q000235:genetics*; D002352:Carrier Proteins / Q000097:blood; D005260:Female; D006023:Glycoproteins / Q000097:blood; D019382:Human Growth Hormone / Q000172:deficiency / Q000378:metabolism*; D006801:Humans; D006946:Hyperinsulinism / Q000150:complications / Q000235:genetics* / Q000378:metabolism; D007118:Immunoassay; D007328:Insulin / Q000097:blood; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D008297:Male; D009154:Mutation; D009765:Obesity / Q000150:complications / Q000235:genetics* / Q000378:metabolism; D044105:Receptor, Melanocortin, Type 4 / Q000172:deficiency / Q000235:genetics*; D012720:Severity of Illness Index; D018709:Statistics, Nonparametric
D002352:Carrier Proteins; D006023:Glycoproteins; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D018972:Insulin-Like Growth Factor Binding Protein 3; D044105:Receptor, Melanocortin, Type 4; C075944:insulin-like growth factor binding protein, acid labile subunit; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II