Identification and functional analysis of novel human growth hormone-releasing hormone receptor (GHRHR) gene mutations in Japanese subjects with short stature.
BACKGROUND
Growth hormone-releasing hormone receptor (GHRHR) gene mutations have been identified in patients of different ethnic origins with isolated GH deficiency (IGHD) type IB. However, the prevalence of these mutations in the Japanese population has yet to be fully determined.


OBJECTIVE
This study aimed to evaluate the contributions of GHRHR mutations to the molecular mechanism underlying short stature in Japanese subjects.


METHODS
The GHRHR gene was sequenced in 127 unrelated Japanese patients with either IGHD (n = 14) or idiopathic short stature (ISS; n = 113). Sequence variants were evaluated in family members and 188 controls, and then examined in functional studies.


RESULTS
A novel homozygous E382E (c.1146G>A) synonymous variant, at the last base of exon 12, was identified in an IGHD family with two affected sisters. In vitro splicing studies showed this mutation to result in skipping of exon 12. In one ISS patient, a heterozygous ATG-166T>C variant was found in the distal Pit-1 P2 binding element of the GHRHR promoter. In two control subjects, a close but distinct variant, ATG-164T>C, was detected. Functional studies showed that both promoter variants diminish promoter activity by altering Pit-1 binding ability. Four missense variants were also found in both patient and control groups but had no detectable functional consequences.


CONCLUSIONS
The homozygous GHRHR mutation was rare, being detected in only one Japanese IGHD family. Future research is needed to clarify the genetic contributions of heterozygous functional promoter variants to GHD, ISS and normal-stature variations.
Division of Genetic Information, Institute for Genome Research, The University of Tokushima, Kuramoto 3-18-15, Tokushima 770-8503, Japan. hinoue@genome.tokushima-u.ac.jp
Hiroshi
H
Inoue
Natsumi
N
Kangawa
Atsuko
A
Kinouchi
Yukiko
Y
Sakamoto
Chizuko
C
Kimura
Reiko
R
Horikawa
Yosuke
Y
Shigematsu
Mitsuo
M
Itakura
Tsutomu
T
Ogata
Kenji
K
Fujieda
D002648:Child; D002675:Child, Preschool; D000242:Cyclic AMP / Q000378:metabolism; D004392:Dwarfism / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D007223:Infant; D008297:Male; D009154:Mutation / Q000235:genetics*; D018013:Receptors, Neuropeptide / Q000235:genetics*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000235:genetics*
D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D000242:Cyclic AMP; C048250:somatotropin releasing hormone receptor