Identification and functional characterization of novel mutations in the melanocortin-4 receptor.
OBJECTIVE
Melanocortin-4 receptor (MC4R) deficiency is the most common cause of monogenic obesity. In the present study, we screened the MC4R gene for mutations in a population of overweight and obese children and adolescents.


METHODS
Cross-sectional mutation analysis of 112 overweight/obese children and adolescents and 121 lean individuals.


RESULTS
We identified 11 sequence variations, 5 of which were present in our control population or had been previously reported as polymorphisms. The remaining 6 variations are disease-causing mutations including 2 novel ones: a I186V mutation and a F280L mutation. The 4 previously described mutations (D90N, M200V, P260Q, Q307X) were identified in single probands. Using confocal imaging, we demonstrated that F280L and P260Q cause intracellular retention of the mutant receptor. No difference in cell surface expression could be detected for the I186V mutation. Using a cAMP responsive luciferase vector, we demonstrated that the receptor with I186V is unable to activate its intracellular signaling pathway while the P260Q mutation causes reduced activation of the receptor.


CONCLUSIONS
We detected MC4R deficiency in 6 patients from our cohort, amounting to a prevalence of 5.3%. Two novel mutations were identified. We also confirmed that intracellular retention is a common pathogenic effect of MC4R mutations.
Beckers
Sigri
S
Department of Medical Genetics, University of Antwerp and Antwerp University Hospital, Antwerp, Belgium.
Zegers
Doreen
D
de Freitas
Fenna
F
Peeters
Armand V
AV
Verhulst
Stijn L
SL
Massa
Guy
G
Van Gaal
Luc F
LF
Timmermans
Jean-Pierre
JP
Desager
Kristine N
KN
Van Hul
Wim
W
D000293:Adolescent; D000328:Adult; D000818:Animals; D001530:Belgium; D015992:Body Mass Index; D001835:Body Weight / Q000235:genetics*; D019556:COS Cells; D016022:Case-Control Studies; D002648:Child; D002522:Chlorocebus aethiops; D003430:Cross-Sectional Studies; D004252:DNA Mutational Analysis; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D018613:Microscopy, Confocal; D009154:Mutation; D009765:Obesity / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D050177:Overweight / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D010375:Pedigree; D010641:Phenotype; D021381:Protein Transport; D044105:Receptor, Melanocortin, Type 4 / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D018570:Risk Assessment; D012307:Risk Factors; D015398:Signal Transduction; D014162:Transfection
C470072:MC4R protein, human; D044105:Receptor, Melanocortin, Type 4