A new missense mutation in the growth hormone-releasing hormone receptor gene in familial isolated GH deficiency.
OBJECTIVE
Mutations in the GH-releasing hormone (GHRH) receptor (GHRHR) gene (GHRHR) cause autosomal recessive familial isolated GH deficiency (IGHD). We searched for GHRHR mutations in two siblings with IGHD type IB and a history of parental consanguinity.


METHODS
We analyzed peripheral genomic DNA of an index patient. After identifying a novel mutation in the GHRHR, we performed functional studies in order to confirm that the mutation causes receptor malfunction.


METHODS
The entire GHRHR was analyzed in the index case by denaturing gradient gel electrophoresis. Abnormally migrating bands were isolated and sequenced. The mutated area was then sequenced in all family members whose DNA was available. The newly found mutation was inserted into a GHRHR cDNA. Wild-type and mutant cDNAs were expressed into CHO cells and the cyclic AMP (cAMP) response to GHRH was measured. In order to determine whether the mutant receptor was properly expressed on the cell membrane surface, CHO cells were transfected with wild-type or mutant GHRHR cDNA containing a FLAG epitope tag in the extracellular N-terminus.


RESULTS
Both patients were homozygous for a new missense mutation in codon 176, corresponding to the second transmembrane domain of the receptor protein that replaces alanine with valine (A176V). The mother and three unaffected siblings were heterozygous for the mutation; DNA from the father was not available. Cells expressing the A176V receptor had a significantly reduced cAMP response to GHRH, despite appropriate expression on the cell surface.


CONCLUSIONS
We describe two siblings with IGHD due to a new mutation in the GHRHR that disrupts GHRH signaling and leads to GHRH resistance.
Carakushansky
Mauri
M
Divisions of Pediatric Endocrinology and Endocrinology and The Ilyssa Center for Molecular and Cellular Endocrinology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
Whatmore
Andrew J
AJ
Clayton
Peter E
PE
Shalet
Stephen M
SM
Gleeson
Helena K
HK
Price
David A
DA
Levine
Michael A
MA
Salvatori
Roberto
R
D002648:Child; D004252:DNA Mutational Analysis; D005192:Family Health; D005260:Female; D015870:Gene Expression; D019382:Human Growth Hormone / Q000172:deficiency*; D006801:Humans; D008297:Male; D020125:Mutation, Missense; D010375:Pedigree; D018013:Receptors, Neuropeptide / Q000235:genetics*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000235:genetics*; D035781:Siblings
D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D019382:Human Growth Hormone; C048250:somatotropin releasing hormone receptor