Commentary: Novel mechanism of pituitary hormone deficiency: genetic variants shift splicing to produce a dominant negative transcription factor isoform

Recent studies have shown a novel mechanism of combined pituitary hormone deficiency associated with mutations in POU1F1, altering the balance of alternative-splicing, which results in over-expression of the beta isoform of POU1F1. These studies underscore the need for biologists, in the context of the routine molecular diagnosis of this condition, to investigate alternative splicing in POU1F1 as well as in other genes.

Postpartum Cranial Diabetes Insipidus

Cranial Diabetes Insipidus is a rare diagnosis and rarer still postpartum. We present the case of 24-year-old woman who developed CDI following pregnancy. The patient had developed persistent polydipsia and polyuria 5 months following her first pregnancy. The pregnancy had been complicated by Gestational Diabetes Mellitus, Obstetric Cholestasis and a Postpartum Haemorrhage which had required a 3 unit transfusion of blood. The patient reported feeling fatigued and lightheaded and stated that she had needed to drink water frequently: around 8 litres throughout the day and 4 litres overnight. She reported that she had been unable to breastfeed but the rest of her systemic enquiry was unremarkable. The patient had attributed her symptoms of lethargy to sleepless nights with her new born baby and the polyuria as a consequence of labour and as such had presented for review at her primary care Physician 18 months following delivery. Initial investigations revealed a fasting blood glucose of 4.9 mmol/l, an Adj. Calcium of 2.23 mmol/l and a fasting urine osmolality of 85 mmol/kg. A diagnosis of DI was suspected and was confirmed by water deprivation test: the patient had an inappropriately dilute urine osmolality of 111 mmol/kg when compared to the serum osmolality of 301 mOsm/Kg at the start of the test and her urine failed to concentrate as water was withheld. Administration of DDAVP resulted in appropriate concentration of urine and therefore confirmed the diagnosis specifically as Cranial Diabetes Insipidus. Blood tests revealed normal anterior pituitary function: TSH was 2.78 mU/L, Prolactin was 361 mU/l, LH and FSH were 23.6 U/L and 5.3 U/L, IGF and GH were 197 ug/L and 0.1 ug/l and ACTH was 10 mU/L. Her basal cortisol was 392 nmol/l and was stimulated to 593 nmol/l by SST. MRI Pituitary revealed an unusually flat and broad pituitary gland with a possible tiny lesion in the posterior pituitary suggestive of an adenoma. The patient was established on DDAVP replacement therapy and her quality of life improved: she enjoyed restful sleep and reported less exhaustion. There was no anterior pituitary hormone deficiency 28 months following delivery. DI is a rare diagnosis with an estimated prevalence of 1 in 25000 people. CDI has been commonly reported as being caused by infiltrative or inflammatory pituitary disease, as an iatrogenic sequelae of pituitary surgery or as a result of a congenital defect in the production of vasopressin. We suspect that in this case the patient’s PPH may have resulted in isolated cranial diabetes insipidus though the significance of the MRI scan findings remains unclear. The learning points highlighted by this case are that CDI can occur following pregnancy in an isolated form without anterior pituitary hormone deficiency. We also highlight that patients may misattribute significant symptoms and signs of DI as being a normal part of the postpartum period resulting in a delayed diagnosis.

Identification of FOXA2 and PNPLA6 Among Other Genes, as a Potential Risk for Pituitary Hormone Deficiency

Pituitary hormone deficiency or hypopituitarism is characterized by a malformed or underdeveloped pituitary gland resulting in an impaired pituitary hormone secretion. Several transcription factors have been described in its etiology, but defects in known genes account for only a small proportion of cases. We sought to identify the cause of hypopituitarism in 171 unrelated patients diagnosed with or without extra-pituitary manifestations that were recruited from several Argentinean medical centers. We conducted panel sequencing, and identified among other genes and variants, de novo heterozygous mutations in FOXA2 and PNPLA6. FOXA2 is a transcription factor member of the forkhead class of DNA-binding proteins, involved in the early development of multiple tissues. FOXA2 is highly expressed throughout the developing hypothalamic-pituitary axis, and regulates GLI2, SHH and NKX2-2 expression. Mutations of FOXA2 have been linked to combined pituitary hormone deficiency (CPHD) in some cases with extra-pituitary phenotypes including hyperinsulinism or gastrointestinal malformations. We found two patients with CPHD and rare FOXA2 variants. Case 1 had GHD, anterior pituitary hypoplasia, mammary hypertelorism and digital anomalies and a heterozygous variant FOXA2 p.Arg228Ser, predicted to be pathogenic. Case 2 had GH and TSH deficiency, craniofacial anomalies and neurodevelopmental delay, and a novel, stop codon mutation FOXA2 p.Ser229* and an heterozygous GLI1 variant (p.Asp1048Asn). Both FOXA2 variants are located within the forkhead domain which may affect the DNA binding ability. We suspect they are likely damaging based on the literature, the in-silico prediction, and their absence in GnomAD. PNPLA6 is a conserved lysophospholipase involved in maintaining nervous system integrity. Mutations in PNPLA6 have been identified in a broad spectrum from pure ataxia to rare neuroendocrine conditions including Gordon Holmes and Oliver McFarlane syndromes. Here, we identified two de novo heterozygous variants in PNPLA6 in children with CPHD. Variant p.W1039R was found in a patient with CPHD, intellectual disability and visual problems. A second variant (p.T1115P) was identified in a 10-year-old girl with CPHD, retinitis pigmentosa and neurodevelopmental delay. According to modelling studies of the protein structure, both variants are expected to be critical for the activity of the NTE as they are located in close proximity to the protein’s catalytic pocket. It is likely that these variants may contribute to our patient’s phenotype. However, as most reported PNPLA6 variants in the literature were found in homozygosity or compound heterozygosity, additional studies are necessary to draw more definitive genotype-phenotype correlations. In summary, in this work we were able to expand our knowledge of pituitary target genes for genetic diagnosis for CH.

High-throughput splicing assays identify missense and silent splice-disruptive POU1F1 variants underlying pituitary hormone deficiency

Pituitary hormone deficiency occurs in ∼1:4,000 live births. Approximately 3% of the cases are due to mutations in the alpha isoform of POU1F1, a pituitary-specific transcriptional activator. We found four separate heterozygous missense variants in unrelated hypopituitarism patients that were predicted to affect a minor isoform, POU1F1 beta, which can act as a transcriptional repressor. These variants retain repressor activity, but they shift splicing to favor the expression of the beta isoform, resulting in dominant negative loss of function. Using a high throughput splicing reporter assay, we tested 1,080 single nucleotide variants in POU1F1. We identified 113 splice disruptive variants, including 23 synonymous variants. We evaluated separate cohorts of hypopituitarism patients and found two different synonymous splice disruptive variants that co-segregate with hypopituitarism. This study underlines the importance of evaluating the impact of variants on splicing and provides a catalog for interpretation of variants of unknown significance in the POU1F1 gene.

Novel STAR gene variant in a patient with classic lipoid congenital adrenal hyperplasia and combined pituitary hormone deficiency

We report the first case of classic lipoid congenital adrenal hyperplasia and combined pituitary hormone deficiency. We identified pathogenic variants in the STAR gene: a novel variant of c.126_127delCCinsG, namely, p.Thr44Profs*2 and an already reported variant of c.634C>T, namely, p.Gln212*. The association with combined pituitary hormone deficiency might be just a coincidence.

A nonsense variant in FGFR1: a rare cause of combined pituitary hormone deficiency

ObjectivesVariants in fibroblast growth factor receptor-1 (FGFR1) may either cause isolated hypogonadotropic hypogonadism (IHH) or Kallmann syndrome (KS). Although the relationship of genes classically involved in IHH with combined pituitary hormone deficiency (CPHD) is well established, variants in FGFR1 have been presented as a rare cause of this phenotype recently.Case presentationHerein, we report an adopted 16-year-old male presented with delayed puberty and micropenis. He had undergone surgery for bilateral undescended testes in childhood. He was normosmic, and the pituitary imaging was normal. However, hypogonadotropic hypogonadism and growth hormone deficiency were detected, associated with a heterozygous nonsense variant (c.1864 C>T, p.R622X) in FGFR1.ConclusionsFGFR1 variants are among the causes of IHH and KS, which are inherited in an autosomal dominant manner and can be associated with midline defects. It should also be kept in mind that CPHD may be associated with FGFR1 variants in a subject with normal olfactory function.