Quelles causes génétiques rechercher en présence d’un déficit en hormone de croissance ?

Abstract

Congenital growth hormone deficiency (GHD) is a rare cause of growth delay. It should be suspected when other causes of hypopituitarism (sellar tumor, postsurgical or radioinduced hypopituitarism, etc.) have been ruled out. GHD can be isolated (IGHD) or associated with at least one other pituitary hormone deficiency (CPHD) including thyrotroph, lactotroph, corticotroph, or gonadotroph deficiencies. CPHD is caused by mutations of genes coding for pituitary transcription factors involved in pituitary ontogenesis or in the hypothalamic-pituitary axis. Clinical presentation varies, depending on the type and severity of GHD, the age at diagnosis, the association with other pituitary hormone deficiencies, or extrapituitary malformations. Clinical, biological, and radiological work-up is very important to determine for which transcription factor the patient should be screened. There is a wide variety of phenotypes depending on the transcription factor involved: PROP1 (somatolactotroph, thyrotroph, gonadotroph, and sometimes corticotroph deficiencies; pituitary hyper- or hypoplasia), POU1F1 (somatolactotroph and thyrotroph deficiencies, pituitary hypoplasia), HESX1 (variable pituitary deficiencies, septo-optic dysplasia), and less frequently LHX3 (somatolactotroph, thyrotroph, and gonadotroph deficiencies, deafness, and limited head and neck rotation), LHX4 (variable pituitary deficiencies, ectopic neurohypophysis, cerebral abnormalities), and OTX2 (variable pituitary deficiencies, ectopic neurohypophysis, ocular abnormalities). Mutations of PROP1 remain the first identified cause of CPHD, and as a consequence the first to be sought. POU1F1 mutations should be looked for in the postpubertal population presenting with GH/TSH deficiencies and no extrapituitary malformations. Once genetic diagnosis has been concluded, a strict follow-up is necessary because patients can develop new deficiencies (for example, late-onset corticotroph deficiency in patients with PROP1 mutations). Identification of gene defects allows early treatment of pituitary deficiency and prevention of their potentially lethal consequences. If untreated, the main symptoms include short stature, cognitive alterations, or delayed puberty. An appropriate replacement of hormone deficiencies is therefore required. Depending on the type of transmission (recessive transmission for PROP1 and LHX3, dominant for LHX4, autosomal dominant or recessive for POU1F1 and HESX1), genetic counseling might be proposed. Genotyping appears highly beneficial at an individual and familial level.