Partial Loss of Function of the GHRH Receptor Leads to Mild Growth Hormone Deficiency

Abstract

Objective: Recessive mutations in GHRHR are associated with severe isolated growth hormone deficiency (IGHD), with a final height in untreated patients of 130 cm ± 10 cm (−7.2 ± 1.6 SDS; males) and 114 ± 0.7 cm (−8.3 ± 0.1 SDS; females). Design: We hypothesized that a consanguineous Pakistani family with IGHD in three siblings (two males, one female) would have mutations in GH1 or GHRHR. Results: Two novel homozygous missense variants [c.11G>A (p.R4Q), c.236C>T (p.P79L)] at conserved residues were identified in all three siblings. Both were absent from control databases, aside from pR4Q appearing once in heterozygous form in the Exome Aggregation Consortium Browser. The brothers were diagnosed with GH deficiency at 9.8 and 6.0 years (height SDS: −2.24 and −1.23, respectively), with a peak GH of 2.9 μg/liter with low IGF-1/IGF binding protein 3. Their sister presented at 16 years with classic GH deficiency (peak GH <0.1 μg/liter, IGF-1 <3.3 mmol/liter) and attained an untreated near-adult height of 144 cm (−3.0 SDS); the tallest untreated patient with GHRHR mutations reported. An unrelated Pakistani female IGHD patient was also compound homozygous. All patients had a small anterior pituitary on magnetic resonance imaging. Functional analysis revealed a 50% reduction in maximal cAMP response to stimulation with GHRH by the p.R4Q/p.P79L double mutant receptor, with a 100-fold increase in EC50. Conclusion: We report the first coexistence of two novel compound homozygous GHRHR variants in two unrelated pedigrees associated with a partial loss of function. Surprisingly, the patients have a relatively mild IGHD phenotype. Analysis revealed that the pP79L mutation is associated with the compromise in function, with the residual partial activity explaining the mild phenotype.