Do common variants separate between obese melanocortin-4 receptor gene mutation carriers and non-carriers? The impact of cryptic relatedness.
OBJECTIVE
Genome-wide association studies revealed associations of single nucleotide polymorphisms (SNPs) flanking MC4R with body mass index variability and obesity. We genotyped 28 SNPs, covering MC4R, and searched for haplotypes discriminating between obese mutation carriers and non-carriers.


METHODS
We analyzed all three-marker haplotype combinations of the 28 SNPs to discriminate between obese mutation carriers and non-carriers - overall and in functional categories for 25 different MC4R mutations: (a) 'like wild type', (b) 'partial loss of function', and (c) 'complete loss of function'. We checked for the possible impact of 'cryptic relatedness' by sensitivity analyses including only 1 randomly selected patient per mutation.


RESULTS
Overall analyses revealed a haplotype of 3 SNPs downstream of the MC4R discriminating between obese mutation carriers and obese non-carriers. However, sensitivity analyses showed that the finding is most likely due to cryptic relatedness.


CONCLUSIONS
Given a mutation prevalence of 1-5%, the sample size of 62 obese mutation carriers with overall 25 different MC4R mutations represents a unique feature of our study. Taking MC4R as an example, we demonstrate the impact of cryptic relatedness when trying to link non-coding SNPs to functionally relevant mutations. Hence, a thorough mutation screen can currently not be guided by SNP genotyping.
Institute of Experimental Pediatric Endocrinology, Charité Campus Virchow-Klinikum, Berlin, Germany.
Jessica
J
Mühlhaus
Carolin
C
Pütter
Harald
H
Brumm
Harald
H
Grallert
Thomas
T
Illig
Susann
S
Scherag
Thomas
T
Reinehr
Wilfried
W
Pott
Özgür
Ö
Albayrak
Hai-Jun
HJ
Wang
Anne-Madeleine
AM
Bau
Susanna
S
Wiegand
Annette
A
Grüters
Heiko
H
Krude
Johannes
J
Hebebrand
Anke
A
Hinney
Heike
H
Biebermann
André
A
Scherag
D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D002648:Child; D004843:Epistasis, Genetic / Q000502:physiology; D005260:Female; D014644:Genetic Variation / Q000502:physiology; D055106:Genome-Wide Association Study; D006579:Heterozygote; D006801:Humans; D008297:Male; D009154:Mutation / Q000502:physiology; D009765:Obesity / Q000453:epidemiology / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide / Q000502:physiology; D044105:Receptor, Melanocortin, Type 4 / Q000235:genetics*; D055815:Young Adult
C470072:MC4R protein, human; D044105:Receptor, Melanocortin, Type 4