Combined pituitary hormone deficiency: current and future status.

Over the last two decades, the understanding of the mechanisms involved in pituitary ontogenesis has largely increased. Since the first description of POU1F1 human mutations responsible for a well-defined phenotype without extra-pituitary malformation, several other genetic defects of transcription factors have been reported with variable degrees of phenotype-genotype correlations. However, to date, despite the identification of an increased number of genetic causes of isolated or multiple pituitary deficiencies, the etiology of most (80-90 %) congenital cases of hypopituitarism remains unsolved. Identifying new etiologies is of importance as a post-natal diagnosis to better diagnose and treat the patients (delayed pituitary deficiencies, differential diagnosis of a pituitary mass on MRI, etc.), and as a prenatal diagnosis to decrease the risk of early death (undiagnosed corticotroph deficiency for instance). The aim of this review is to summarize the main etiologies and phenotypes of combined pituitary hormone deficiencies, associated or not with extra-pituitary anomalies, and to suggest how the identification of such etiologies could be improved in the near future.

[Genetic aspects of growth hormone deficiency]. / Quelles causes génétiques rechercher en présence d'un déficit en hormone de croissance ?

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.

A novel dysfunctional LHX4 mutation with high phenotypical variability in patients with hypopituitarism.

CONTEXT: LHX4 is a LIM homeodomain transcription factor involved in pituitary ontogenesis. Only a few heterozygous LHX4 mutations have been reported to be responsible for congenital pituitary hormone deficiency. SUBJECTS AND METHODS: A total of 136 patients with congenital hypopituitarism associated with malformations of brain structures, pituitary stalk, or posterior pituitary gland was screened for LHX4 mutations. RESULTS: Three novel allelic variants that cause predicted changes in the protein sequence of LHX4 (2.3%) were found (p.Thr99fs, p.Thr90Met, and p.Gly370Ser). On the basis of functional studies, p.Thr99fs mutation was responsible for the patients' phenotype, whereas p.Thr90Met and p.Gly370Ser were likely polymorphisms. Patients bearing the heterozygous p.Thr99fs mutation had variable phenotypes: two brothers presented somato-lactotroph and thyrotroph deficiencies, with pituitary hypoplasia and poorly developed sella turcica; the youngest brother (propositus) also had corpus callosum hypoplasia and ectopic neurohypophysis; their father only had somatotroph deficiency and delayed puberty with pituitary hyperplasia. Functional studies showed that the mutation induced a complete loss of transcriptional activity on POU1F1 promoter and a lack of DNA binding. Cotransfection of p.Thr99fs mutant and wild-type LHX4 failed to evidence any dominant negative effect, suggesting a mechanism of haploinsufficiency. We also identified prolactin and GH promoters as potential target genes of LHX4 and found that the p.Thr99fs mutant was also unable to transactivate these promoters. CONCLUSIONS: The present report describes three new exonic LHX4 allelic variants with at least one being responsible for congenital hypopituitarism. It also extends the phenotypical heterogeneity associated with LHX4 mutations, which includes variable anterior pituitary hormone deficits, as well as pituitary and extrapituitary abnormalities.

[Clinical and genetic aspects of combined pituitary hormone deficiencies]. / Déficit hypophysaire combiné multiple : aspects cliniques et génétiques.

DEFINITION: Congenital hypopituitarism is characterized by multiple pituitary hormone deficiency, including somatotroph, thyrotroph, lactotroph, corticotroph or gonadotroph deficiencies, due to mutations of pituitary transcription factors involved in pituitary ontogenesis. INCIDENCE: Congenital hypopituitarism is rare compared with the high incidence of hypopituitarism induced by pituitary adenomas, transsphenoidal surgery or radiotherapy. The incidence of congenital hypopituitarism is estimated to be between 1:3000 and 1:4000 births. CLINICAL SIGNS: Clinical presentation is variable, depending on the type and severity of deficiencies and on the age at diagnosis. If untreated, main symptoms include short stature, cognitive alterations or delayed puberty. DIAGNOSIS: A diagnosis of combined pituitary hormone deficiency (CPHD) must be suspected when evident causes of hypopituitarism (sellar tumor, postsurgical or radioinduced hypopituitarism...) have been ruled out. Clinical, biological and radiological work-up is very important to better determine which transcription factor should be screened. Confirmation is provided by direct sequencing of the transcription factor genes. AETIOLOGY: Congenital hypopituitarism is due to mutations of several genes encoding pituitary transcription factors. Phenotype varies with the factor involved: PROP1 (somatolactotroph, thyrotroph, gonadotroph and sometimes corticotroph deficiencies; pituitary hyper and hypoplasia), POU1F1 (somatolactotroph and thyrotroph deficiencies, pituitary hypoplasia), HESX1 (variable pituitary deficiencies, septo-optic dysplasia), and less frequently LHX3 (somatolactotroph, thyrotroph and gonadotroph deficiencies, limited head and neck rotation) and LHX4 (variable pituitary deficiencies, ectopic neurohypophysis, cerebral abnormalities). MANAGEMENT: An appropriate replacement of hormone deficiencies is required. Strict follow-up is necessary because patients develop new deficiencies (for example late onset corticotroph deficiency in patients with PROP1 mutations). GENETIC COUNSELLING: Type of transmission varies with the factor and the mutation involved (recessive transmission for PROP1 and LHX3, dominant for LHX4, autosomal or recessive for POU1F1 and HESX1). PROGNOSIS: It is equivalent to patients without pituitary deficiencies if treatment is started immediately when diagnosis is confirmed, and if a specialized follow-up is performed.

Pituitary transcription factors: from congenital deficiencies to gene therapy.

Despite the existence of interspecies phenotypic variability, animal models have yielded valuable insights into human pituitary diseases. Studies on Snell and Jackson mice known to have growth hormone, prolactin and thyroid-stimulating hormone deficiencies involving the hypoplastic pituitary gland have led to identifying alterations of the pituitary specific POU homeodomain Pit-1 transcription factor gene. The human phenotype associated with rare mutations in this gene was found to be similar to that of these mice mutants. Terminal differentiation of lactotroph cells and direct regulation of the prolactin gene both require interactions between Pit-1 and cell type specific partners, including panpituitary transcriptional regulators such as Pitx1 and Pitx2. Synergistic activation of the prolactin promoter by Pitx factors and Pit-1 is involved not only in basal condition, but also in responsiveness to forskolin, thyrotrophin-releasing-hormone and epidermal growth factor. In corticotroph cells, Pitx1 interacts with Tpit. Tpit mutations have turned out to be the main molecular cause of neonatal isolated adrenocorticotrophin deficiency. This finding supports the idea that Tpit plays an essential role in the differentiation of the pro-opiomelanocortin pituitary lineage. The effects of Pit-1 are not restricted to hormone gene regulation because this factor also contributes to cell division and protects the cell from programmed cell death. Lentiviral vectors expressing a Pit-1 dominant negative mutant induced time- and dose-dependent cell death in somatotroph and lactotroph adenomas in vitro. Gene transfer by lentiviral vectors should provide a promising step towards developing an efficient specific therapeutic approach by which a gene therapy programme for treating human pituitary adenomas could be based.

Alteration of striatal dopaminergic function induced by glioma development: a microdialysis and immunohistological study in the rat striatum.

Tumoral growth effects on brain circuitry and neurochemical activities remain poorly documented. This study evaluates C6 graft effects on striatal dopaminergic afferent projections at both anatomical and functional levels. Immunohistochemistry was performed to investigate changes in neurofilament (NF), tyrosine hydroxylase (TH) and dopamine transporter (DAT) expression. Dopaminergic turnover was assessed using multiprobe microdialysis in freely-moving rat. In C6 graft striatum, dopamine (DA) catabolites were reduced in glioblastoma (DOPAC: -61%, HVA: -62%). In contrast, the DA level remained unchanged. Staining for NF, TH and DAT was drastically decreased inside the tumor. Our histological data report that striatal tumoral growth is associated with a decrease in the density of dopaminergic endings which can explain, at least in part, the decrease in DA turnover. The decrease in DAT transporter expression and the lack of change in DA level may result from an increase in DA diffusion from the peripheral areas of the tumor. In conclusion, glioblastoma growth has major consequences on the local neuronal circuitry and its neurochemistry. Changes in inter-connections and neurotransmitter turnover may result in abnormal neuronal firing activity and participate in clinical disorders associated with glioblastoma diagnosis.

In vivo study of tumor metabolism: an application of new multi-probe microdialysis system in the striatum of freely moving rats grafted with C6 cells.

The purpose of this study is to investigate the in vivo tumoral brain metabolism in free moving rats using microdialysis. Cells from C6 glioma cell line were inoculated in one striatum 15 days before the microdialysis experimentation. Then, using a new system allowing perfusion of several microdialysis probes in free moving rat, normalised dialysate levels of glucose, lactate and pyruvate were monitored in both glioma and control striatum. At the end of the procedure, animals were sacrificed for histological study. Data shows that probe functioning is similar in both tissues. The results for normalised glucose level were in striatum control: 2.14 mM, in tumoral striatum: 1.71 mM (P>0.1); for lactate, respectively, 0.86 and 1.65 mM (P<0.05) and for pyruvate, respectively, 65.56 and 140. 94 microM (P<0.05). This data clearly shows a significant increase of pyruvate and lactate in tumoral striatum compared to normal striatum, correlating previous in vitro studies on glioma metabolism. We conclude that this microdialysis technique is of value in tumoral brain and could constitute an interesting tool for a better understanding of glioma metabolism.