Background: Mutations in the gene encoding LHX4, a homeodomain-containing factor with two LIM domains, are responsible for dominant hypopituitarisms with incomplete penetrance and variable expressivity. To date, only 14 unambiguous LHX4 mutations have been reported. Among those cases, 12 had an absent or ectopic posterior pituitary (EPP) and/or an abnormal sella turcica.
Objective and hypotheses: To i) assess the contribution of LHX4 in combined pituitary hormone deficits, and ii) assess the functional consequences of the identified variants and the role of LHX4 LIM domains.
Method: We screened a group of 510 independent patients presenting with various pituitary hormone deficits associated with an EPP and/or sella turcica anomalies. The functional consequences of the variants identified and LIM1- or LIM2-defective variants were assessed by luciferase assay, immunocytofluorescence and co-immunoprecipitation studies.
Results: LHX4 heterozygous variations were identified: 4 truncating mutations [p.(Tyr131*), p.(Arg48Thrfs*104), c.607-1G>C, c.606+1G>T], 3 LIM1 missense variants [p.Lys40Asn, p.Ala65Val, p.Arg71Lys] and 3 missense variations located in the homeodomain area [p.Thr163Pro, p.Arg221Gln, p.Arg235Gln]. Truncating mutations (p.(Tyr131*) and p.(Arg48Thrfs*104)) and the homeodomain missense variant p.Thr163Pro were unable to transactivate POU1F1, GH and PRL proximal promoters. Putative truncated proteins displayed a cytoplasmic localisation; however the corresponding transcripts are likely to be subjected to mRNA decay. All missense variants were found to be expressed in the nucleus. Interaction studies between LHX4 and different protein partners did not unveil any loss of interaction for the missense variants located in the LIM1 domain. Deletion of the LIM1 domain altered LHX4 transactivation capacity, whereas a LIM2-domain deletion abolished LHX4 interaction with ISL2 and LDB1.
Conclusion: This study, performed in the largest cohort of patients so far screened for LHX4 mutations, shows that this gene is responsible for at most 1% (5/510 independent probands) of hypopituitarisms. This work also highlights the respective roles of LIM1 and LIM2 domains.
10 - 12 Sep 2016
European Society for Paediatric Endocrinology