Isolated growth hormone (GH) deficiency due to compound heterozygosity for two new mutations in the GH-releasing hormone receptor gene

OBJECTIVE: Mutations in the GH releasing hormone receptor (GHRH-R) have recently been shown to cause autosomal recessive isolated GH deficiency (IGHD). Patients who are homozygous for GHRH-R mutations have a subnormal GH response to pharmacological agents that stimulate GH secretion and an appropriate response to exogenous GH therapy. We searched for mutations in the GHRH-R gene in a family in which two of three siblings were affected by IGHD. DESIGN: We sequenced the 13 coding exons, the intron-exon boundaries and 327 bases of the promoter of the GHRH-R gene from peripheral blood cell genomic DNA of an index patient. RESULTS: Both affected individuals were compound heterozygotes for two previously undescribed GHRH-R mutations: a change in codon 137 that replaces histidine with leucine (H137L), and a 5 bp deletion in exon 11 (Del 1140-1144). The patients' father was heterozygous for the H137L mutation, and the mother was heterozygous for the exon 11 deletion. We used site-directed mutagenesis to create the mutants in wild-type GHRH-R cDNA. Transient transfection of GHRH-R cDNAs in Chinese hamster ovary cells showed that cells transfected with both mutant receptors failed to increase cyclic AMP after treatment with GHRH. CONCLUSIONS: We describe a family in which two siblings with IGHD were compound heterozygotes for two new mutations in the GHRH-R gene. These results suggest that mutant alleles for GHRH-R gene may be more common than previously suspected.