Katsura Ishizu

OTX2 loss of function mutation causes anophthalmia and combined pituitary hormone deficiency with a small anterior and ectopic posterior pituitary.

CONTEXT Orthodenticle homeobox 2 (OTX2) is a transcription factor necessary for ocular and forebrain development. In humans, heterozygous mutations of OTX2 cause severe ocular malformations. However, whether mutations of OTX2 cause pituitary structural abnormalities or combined pituitary hormone deficiency (CPHD) has not been clarified. OBJECTIVES We surveyed the functional consequences of a novel OTX2 mutation that was detected in a patient with anophthalmia and CPHD. PATIENT We examined a Japanese patient with growth disturbance, anophthalamia, and severe developmental delay. He showed deficiencies in GH, TSH, LH, FSH, and ACTH. Brain magnetic resonance imaging revealed a small anterior pituitary gland, invisible stalk, ectopic posterior lobe, and Chiari malformation. RESULTS Sequence analysis of OTX2 demonstrated a heterozygous two bases insertion [S136fsX178 (c.576-577insCT)] in exon 3. The mutant Otx2 protein localized to the nucleus, but did not activate the promoter of the HESX1 and POU1F1 gene, indicating a loss of function mutation. No dominant negative effect in the presence of wild-type Otx2 was observed. CONCLUSION This case indicates that the OTX2 mutation is a cause of CPHD. Further study of more patients with OTX2 defects is necessary to clarify the clinical phenotypes and endocrine defects caused by OTX2 mutations.

Three Novel IGSF1 Mutations in Four Japanese Patients With X-Linked Congenital Central Hypothyroidism

CONTEXT Congenital central hypothyroidism (C-CH) is a rare disease. We investigated the molecular basis of unexplained C-CH in 4 Japanese boys. PATIENTS AND METHODS C-CH was diagnosed by low free T4 and/or T3 and low basal TSH concentrations. We used whole-exome sequencing of one patient with C-CH to identify potential disease-causing mutations. Thereafter, PCR direct sequencing was performed to Identify genetic defects underlying C-CH in 3 more patients. We then assessed the effects of mutations identified in the Ig superfamily, member 1 (IGSF1), gene on protein expression and membrane trafficking. RESULTS All patients had congenital hypothyroidism, and 2 had definitive prolactin deficiency. Two patients were detected by neonatal screening. The other patients were diagnosed by short stature and failure to thrive. We identified a novel nonsense variant in IGSF1 by whole-exome sequencing in patient 1, which was confirmed by PCR direct sequencing (p.R1189X). PCR direct sequencing identified the identical nonsense mutation in patient 2. Patients 3 and 4 harbored distinct missense (p.V1082E) or nonsense (p.Q645X) mutations in IGSF1. The mothers of patients 1, 3, and 4 were heterozygous for these mutations. The R1189X mutant, which lacks the transmembrane domain, failed to traffic to the plasma membrane. V1082E could be observed at the cell surface, but at greatly diminished levels relative to the wild-type form of the protein. The severely truncated Q645X mutant could not be detected by Western blot. CONCLUSION Our findings provide additional genetic evidence that loss-of-function mutations in IGSF1 cause an X-linked form of C-CH and variable prolactin deficiency.

A novel mutation (V101A) of the LHX4 gene in a Japanese patient with combined pituitary hormone deficiency.

OBJECTIVE LHX4, a LIM-homeodomain transcription factor, is required for development of the pituitary and nervous system. Several mutations of the LHX4 gene have been identified in patients with combined pituitary hormone deficiency (CPHD). The objective of the study was to clarify the molecular basis of a Japanese patient of CPHD with a small anterior pituitary and an ectopic posterior pituitary. METHODS Genomic DNA was extracted from blood samples of the patient. Exons and exon-intron junctions of the LHX4 gene were amplified and sequenced. An expression vector of the mutant LHX4 protein was constructed and its function was analyzed in vitro. RESULTS A novel missense mutation (V101A) was identified. IN VITRO transfection studies demonstrated that V101A mutant LHX4 was unable to activate the POU1F1 and FSHbeta subunit gene promoter, indicating a loss of function mutation. CONCLUSION Our results identify a novel loss of function mutation of the LHX4 gene in a Japanese patient with CPHD.

Congenital Hypothyroidism Caused by a PAX8 Gene Mutation Manifested as Sodium/Iodide Symporter Gene Defect.

Loss-of-function mutations of the PAX8 gene are considered to mainly cause congenital hypothyroidism (CH) due to thyroid hypoplasia. However, some patients with PAX8 mutation have demonstrated a normal-sized thyroid gland. Here we report a CH patient caused by a PAX8 mutation, which manifested as iodide transport defect (ITD). Hypothyroidism was detected by neonatal screening and L-thyroxine replacement was started immediately. Although 123I scintigraphy at 5 years of age showed that the thyroid gland was in the normal position and of small size, his iodide trapping was low. The ratio of the saliva/plasma radioactive iodide was low. He did not have goiter; however laboratory findings suggested that he had partial ITD. Gene analyses showed that the sodium/iodide symporter (NIS) gene was normal; instead, a mutation in the PAX8 gene causing R31H substitution was identified. The present report demonstrates that individuals with defective PAX8 can have partial ITD, and thus genetic analysis is useful for differential diagnosis.

Molecular and Clinical Findings in Patients with LHX4 and OTX2 Mutations

The pituitary gland produces hormones that play important roles in both the development and homeostasis of the body. Ontogeny of the anterior and posterior pituitary is orchestrated by inputs from neighboring tissues, cellular signaling molecules and transcription factors. Disruption of expression or function of these factors has been implicated in the etiology of combined pituitary hormone deficiency (CPHD). These include the transcription factors HESX1, PROP1, POU1F1, LHX3, LHX4, OTX2, SOX2, SOX3 and GLI2. This review focuses on summarizing most recent mutations in LHX4 and OTX2 responsible for pituitary hormone deficiency. In both genetic defects of LHX4 and OTX2, there is high variability in clinical manifestations even in the same family. In addition, there is no clear phenotype-genotype correlation. These findings indicate that the other genetic and/or environmental factors influence the phenotype. In addition, the variability might reflect a plasticity during pituitary development and maintenance. Over the past two decades, a genetic basis for pituitary hormone deficiency and the mechanism of pituitary development have been clarified. It should be kept in mind that this review is not comprehensive, and defects of other transcriptional factors have been described in patients with CPHD. Furthermore, the causes in many patients with CPHD have not yet been determined. Therefore, continuing efforts for the clarification of the etiology are necessary.

Loss-of-Function and Gain-of-Function Mutations of Calcium-Sensing Receptor: Functional Analysis and the Effect of Allosteric Modulators NPS R-568 and NPS 2143

OBJECTIVE Activating mutations in the calcium-sensing receptor (CASR) gene cause autosomal dominant hypoparathyroidism, and heterozygous inactivating CASR mutations cause familial hypocalciuric hypercalcemia. Recently, there has been a focus on the use of allosteric modulators to restore the functional activity of mutant CASRs. In this study, the effect of allosteric modulators NPS R-568 and NPS 2143 on CASR mutants was studied in vitro. METHODS DNA sequence analysis of the CASR gene was undertaken in autosomal dominant hypoparathyroidism and familial hypocalciuric hypercalcemia Japanese patients, and the functional consequences for the Gi-MAPK pathway and cell surface expression of CASR were determined. Furthermore, we studied the effect of NPS R-568 and NPS 2143 on the signal transduction activity and cell surface expression of each mutant CASR. RESULTS We identified 3 activating mutations (S122C, P569H, and I839T) and 2 inactivating mutations (A110T and R172G) in patients. The activating and inactivating mutations caused leftward and rightward shifts, respectively, in the dose-response curves of the signaling pathway. NPS R-568 rescued the signal transduction capacity of 2 inactivating mutants without increasing cell surface expression levels. NPS 2143 suppressed the enhanced activity of the activating mutants without altering cell surface expression levels, although A843E, which is a constitutively active mutant, was suppressed to a lesser degree. CONCLUSIONS We have identified 4 novel mutations of CASR. Moreover, our results indicate that allosteric modulators can restore the activity of the loss- and gain-of-function mutant CASRs, identified in this study.

Two Children with Xanthogranuloma of the Sellar Region

We report the cases of two Japanese children with cystic pituitary enlargement on magnetic resonance imaging (MRI) causing central diabetes insipidus (DI). In the first patient, endocrinological examination demonstrated slightly impaired growth hormone and thyroid stimulating hormone secretions, but normal responses of other anterior pituitary hormones. The second patient had normal basal levels of anterior pituitary hormones. Transsphenoidal resection of the tumors was performed in both patients. Histological analysis of the tumor sections demonstrated granulomatous tissue with cholesterol clefts, foamy macrophages, multinucleated giant cells and no epithelial component. Thus, these tumors were pathologically diagnosed as xanthogranuloma of the sellar region, different from adamantinomatous craniopharyngioma. Post-operatively, the two patients continue to have DI, however other hormone replacement therapy after one year of follow-up has not been required. Currently, it is not clear whether xanthogranuloma is a distinct entity from adamantinomatous craniopharyingioma. Although, to our knowledge, a clinical report of xanthogranuloma of the sellar region has not been reported at pediatric age, it would be included in the differential diagnosis of the sellar region.

A novel heterozygous mutation of the WFS1 gene leading to constitutive endoplasmic reticulum stress is the cause of Wolfram syndrome

Wolfram syndrome (WS) is a disorder characterized by the association of insulin‐dependent diabetes mellitus (DM), diabetes insipidus, deafness, and optic nerve atrophy. WS is caused by WFS1 mutations encoding WFS1 protein expressed in endoplasmic reticulum (ER). During ER protein synthesis, misfolded and unfolded proteins accumulate, known as “ER stress”. This is attenuated by the unfolded protein response (UPR), which recovers and maintains ER functions. Because WFS1 is a UPR component, mutant WFS1 might cause unresolvable ER stress conditions and cell apoptosis, the major causes underlying WS symptoms. We encountered an 11‐month‐old Japanese female WS patient with insulin‐dependent DM, congenital cataract and severe bilateral hearing loss.

Neonatal screening and a new cause of congenital central hypothyroidism

Congenital central hypothyroidism (C-CH) is a rare disease in which thyroid hormone deficiency is caused by insufficient thyrotropin (TSH) stimulation of a normally-located thyroid gland. Most patients with C-CH have low free thyroxine levels and inappropriately low or normal TSH levels, although a few have slightly elevated TSH levels. Autosomal recessive TSH deficiency and thyrotropin-releasing hormone receptor-inactivating mutations are known to be genetic causes of C-CH presenting in the absence of other syndromes. Recently, deficiency of the immunoglobulin superfamily member 1 (IGSF1) has also been demonstrated to cause C-CH. IGSF1 is a plasma membrane glycoprotein highly expressed in the pituitary. Its physiological role in humans remains unknown. IGSF1 deficiency causes TSH deficiency, leading to hypothyroidism. In addition, approximately 60% of patients also suffer a prolactin deficiency. Moreover, macroorchidism and delayed puberty are characteristic features. Thus, although the precise pathophysiology of IGSF1 deficiency is not established, IGSF1 is considered to be a new factor controlling growth and puberty in children.

Two heterozygous mutations of the AMH gene in a Japanese patient with persistent Müllerian duct syndrome

Abstract Persistent Müllerian duct syndrome (PMDS) is an autosomal recessive disorder of sex development (DSD) characterized by the presence of Müllerian duct derivatives in 46, XY phenotypic males. To date, more than 50 different mutations of the anti-Müllerian hormone gene (AMH) have been reported. Here, we report two novel mutations of AMH in a Japanese patient with PMDS. A 1-year-old male presented with bilateral cryptorchidism and normal male external genitalia. A laparoscopic surgery revealed a uterus and fallopian tubes. Serum AMH was very low. The patient’s elder brother was also diagnosed as having PMDS at another hospital. Genetic analysis of AMH showed two novel mutations of p.N486T and p.V527L. Given that these two amino acids are well conserved among different species of AMH, the substitution of two amino acids might affect the normal function of AMH. In conclusion, PMDS should be included in differential diagnoses of cryptorchidism.