Functional Analysis of a Novel HNF4A Variant Identified in a Patient With MODY1.

Context: HNF4A-maturity-onset diabetes of the young (MODY1) is a relatively rare subtype of monogenic diabetes caused by loss of function of the HNF4A gene, which encodes the transcription factor HNF4α. HNF4α is known to form heterodimers, and the various combinations of isoforms that make up these heterodimers have been reported to result in a diversity of targeted genes. However, the function of individual HNF4α variant isoforms and the heterodimers comprising both wild-type (WT) and variant HNF4α have not yet been assessed. Objective: In this study, we analyzed the functional consequence of the HNF4A D248Y variant in vitro. Methods: We investigated the case of a 12-year-old Japanese girl who developed diabetes at age 11 years. Genetic sequencing detected a novel heterozygous missense HNF4A variant (c.742G > T, p.Asp248Tyr; referred as "D248Y") in the patient and her relatives who presented with diabetes. Results: Although the WT HNF4α isoforms (HNF4α2, HNF4α3, HNF4α8, HNF4α9) enhanced the INS gene promoter activity in HepG2 cells, the promoter activity of D248Y was consistently low across all isoforms. The presence of D248Y in homodimers and heterodimers, comprising either HNF4α8 or HNF4α3 or a combination of both isoforms, also reduced the INS promoter activity in Panc-1 cells. Conclusion: We report the clinical course of a patient with HNF4A-MODY and the functional analysis of novel HNF4A variants, with a focus on the isoforms and heterodimers they form. Our results serve to improve the understanding of the dominant-negative effects of pathogenic HNF4A variants.

Comprehensive overview of disease models for Wolfram syndrome: toward effective treatments.

Wolfram syndrome (OMIM 222300) is a rare autosomal recessive disease with a devastating array of symptoms, including diabetes mellitus, optic nerve atrophy, diabetes insipidus, hearing loss, and neurological dysfunction. The discovery of the causative gene, WFS1, has propelled research on this disease. However, a comprehensive understanding of the function of WFS1 remains unknown, making the development of effective treatment a pressing challenge. To bridge these knowledge gaps, disease models for Wolfram syndrome are indispensable, and understanding the characteristics of each model is critical. This review will provide a summary of the current knowledge regarding WFS1 function and offer a comprehensive overview of established disease models for Wolfram syndrome, covering animal models such as mice, rats, flies, and zebrafish, along with induced pluripotent stem cell (iPSC)-derived human cellular models. These models replicate key aspects of Wolfram syndrome, contributing to a deeper understanding of its pathogenesis and providing a platform for discovering potential therapeutic approaches.

Palmitoylation couples insulin hypersecretion with ß cell failure in diabetes.

Hyperinsulinemia often precedes type 2 diabetes. Palmitoylation, implicated in exocytosis, is reversed by acyl-protein thioesterase 1 (APT1). APT1 biology was altered in pancreatic islets from humans with type 2 diabetes, and APT1 knockdown in nondiabetic islets caused insulin hypersecretion. APT1 knockout mice had islet autonomous increased glucose-stimulated insulin secretion that was associated with prolonged insulin granule fusion. Using palmitoylation proteomics, we identified Scamp1 as an APT1 substrate that localized to insulin secretory granules. Scamp1 knockdown caused insulin hypersecretion. Expression of a mutated Scamp1 incapable of being palmitoylated in APT1-deficient cells rescued insulin hypersecretion and nutrient-induced apoptosis. High-fat-fed islet-specific APT1-knockout mice and global APT1-deficient db/db mice showed increased ß cell failure. These findings suggest that APT1 is regulated in human islets and that APT1 deficiency causes insulin hypersecretion leading to ß cell failure, modeling the evolution of some forms of human type 2 diabetes.

Loss of Function of WFS1 Causes ER Stress-Mediated Inflammation in Pancreatic Beta-Cells.

Wolfram syndrome is a rare genetic disorder characterized by juvenile-onset diabetes mellitus, optic nerve atrophy, hearing loss, diabetes insipidus, and progressive neurodegeneration. Pathogenic variants in the WFS1 gene are the main causes of Wolfram syndrome. WFS1 encodes a transmembrane protein localized to the endoplasmic reticulum (ER) and regulates the unfolded protein response (UPR). Loss of function of WFS1 leads to dysregulation of insulin production and secretion, ER calcium depletion, and cytosolic calpains activation, resulting in activation of apoptotic cascades. Although the terminal UPR has been shown to induce inflammation that accelerates pancreatic ß-cell dysfunction and death in diabetes, the contribution of pancreatic ß-cell inflammation to the development of diabetes in Wolfram syndrome has not been fully understood. Here we show that WFS1-deficiency enhances the gene expression of pro-inflammatory cytokines and chemokines, leading to cytokine-induced ER-stress and cell death in pancreatic ß-cells. PERK and IRE1α pathways mediate high glucose-induced inflammation in a ß-cell model of Wolfram syndrome. M1-macrophage infiltration and hypervascularization are seen in the pancreatic islets of Wfs1 whole-body knockout mice, demonstrating that WFS1 regulates anti-inflammatory responses in pancreatic ß-cells. Our results indicate that inflammation plays an essential role in the progression of ß-cell death and diabetes in Wolfram syndrome. The pathways involved in ER stress-mediated inflammation provide potential therapeutic targets for the treatment of Wolfram syndrome.

The Role of ER Stress in Diabetes: Exploring Pathological Mechanisms Using Wolfram Syndrome.

The endoplasmic reticulum (ER) is a cytosolic organelle that plays an essential role in the folding and processing of new secretory proteins, including insulin. The pathogenesis of diabetes, a group of metabolic disorders caused by dysfunctional insulin secretion (Type 1 diabetes, T1DM) or insulin sensitivity (Type 2 diabetes, T2DM), is known to involve the excess accumulation of "poorly folded proteins", namely, the induction of pathogenic ER stress in pancreatic ß-cells. ER stress is known to contribute to the dysfunction of the insulin-producing pancreatic ß-cells. T1DM and T2DM are multifactorial diseases, especially T2DM; both environmental and genetic factors are involved in their pathogenesis, making it difficult to create experimental disease models. In recent years, however, the development of induced pluripotent stem cells (iPSCs) and other regenerative technologies has greatly expanded research capabilities, leading to the development of new candidate therapies. In this review, we will discuss the mechanism by which dysregulated ER stress responses contribute to T2DM pathogenesis. Moreover, we describe new treatment methods targeting protein folding and ER stress pathways with a particular focus on pivotal studies of Wolfram syndrome, a monogenic form of syndromic diabetes caused by pathogenic variants in the WFS1 gene, which also leads to ER dysfunction.

A soluble endoplasmic reticulum factor as regenerative therapy for Wolfram syndrome.

Endoplasmic reticulum (ER) stress-mediated cell death is an emerging target for human chronic disorders, including neurodegeneration and diabetes. However, there is currently no treatment for preventing ER stress-mediated cell death. Here, we show that mesencephalic astrocyte-derived neurotrophic factor (MANF), a neurotrophic factor secreted from ER stressed cells, prevents ER stress-mediated ß cell death and enhances ß cell proliferation in cell and mouse models of Wolfram syndrome, a prototype of ER disorders. Our results indicate that molecular pathways regulated by MANF are promising therapeutic targets for regenerative therapy of ER stress-related disorders, including diabetes, retinal degeneration, neurodegeneration, and Wolfram syndrome.

Targeted Next-Generation Sequencing for Congenital Hypothyroidism With Positive Neonatal TSH Screening.

PURPOSE: Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder; however, its molecular etiology remains poorly understood. METHODS: We performed genetic analysis of 24 causative genes using next-generation sequencing in 167 CH cases, comprising 57 dyshormonogenesis (DH), 32 dysgenesis (TD) and 78 undiagnosed. The pathogenicity of variants was assessed by the American College of Medical Genetics guidelines, inheritance pattern, and published evidence. Furthermore, we compared the oligogenic groups and monogenic groups to examine the correlation between variant dosage and severity. RESULTS: We identified variants in 66.5% cases (111/167) and 15 genes, DUOX2, TSHR, PAX8, TG, TPO, DUOXA2, JAG1, GLIS3, DUOX1, IYD, SLC26A4, SLC5A5, SECISBP2, DIO1, and DIO3. Biallelic variants were identified in 12.6% (21/167), oligogenic in 18.0% (30/167), and monogenic in 35.9% (60/167); however, 68.5% of variants were classified as variant of unknown significance (VUS). Further examinations showed that 3 out of 32 cases with TD (9.4%) had pathogenic variants (2 of TSHR and 1 of TPO), and 8 out of 57 cases with DH (14.0%) (7 of DUOX2, 1 of TG) had pathogenic variants. In addition, TSH levels at the first visit were significantly higher in the oligogenic group than in the monogenic group. CONCLUSIONS: The detection rate of pathogenic variants in Japanese CH was similar to that previously reported. Moreover, oligogenic cases were likely to be more severe than monogenic cases, suggesting that CH may exhibit a gene dosage effect. Further analysis of VUS pathogenicity is required to clarify the molecular basis of CH.

Gene-edited human stem cell-derived ß cells from a patient with monogenic diabetes reverse preexisting diabetes in mice.

Differentiation of insulin-producing pancreatic ß cells from induced pluripotent stem cells (iPSCs) derived from patients with diabetes promises to provide autologous cells for diabetes cell replacement therapy. However, current approaches produce patient iPSC-derived ß (SC-ß) cells with poor function in vitro and in vivo. Here, we used CRISPR-Cas9 to correct a diabetes-causing pathogenic variant in Wolfram syndrome 1 (WFS1) in iPSCs derived from a patient with Wolfram syndrome (WS). After differentiation to ß cells with our recent six-stage differentiation strategy, corrected WS SC-ß cells performed robust dynamic insulin secretion in vitro in response to glucose and reversed preexisting streptozocin-induced diabetes after transplantation into mice. Single-cell transcriptomics showed that corrected SC-ß cells displayed increased insulin and decreased expression of genes associated with endoplasmic reticulum stress. CRISPR-Cas9 correction of a diabetes-inducing gene variant thus allows for robust differentiation of autologous SC-ß cells that can reverse severe diabetes in an animal model.

(Epi)genetic defects of MKRN3 are rare in Asian patients with central precocious puberty.

We sequenced MKRN3, the major causative gene of central precocious puberty in Western countries, in 24 Japanese or Chinese patients and examined the DNA methylation and copy-number statuses of this gene in 19 patients. We identified no (epi)genetic defects except for one previously reported mutation. These results, together with reports from Korea, indicate that MKRN3 defects are rare in Asian populations. The ethnic differences likely reflect Western country-specific founder mutations and the rarity of de novo mutations.

Hypoglycemia in type 1A diabetes can develop before insulin therapy: A retrospective cohort study.

AIMS: There are as yet no cohort studies of hypoglycemia in type 1 diabetes before starting insulin therapy. Our aim was to determine the frequency and clinical features of hypoglycemia in patients with type 1A diabetes prior to commencing insulin therapy. METHODS: Eighty-seven patients with type 1A diabetes were enrolled, and a retrospective chart review of the patients was conducted. RESULTS: Hypoglycemia before insulin therapy occurred in six of 87 patients (6.9%). The HbA1c levels at the diagnosis of type 1A diabetes in the hypoglycemia group were lower than in the non-hypoglycemia group (median: 7.3% (56 mmol/mol) vs. 11.9% (106 mmol/mol), p < 0.0001). Similarly, the 24-hour urinary C-peptide (UCPR) levels of the former group were higher than those of the latter group (16.5 µg/day/m2 vs. 7.0 µg/day/m2, p = 0.0075). Hypoglycemic episodes occurred mostly in the postprandial period and gradually disappeared with a decrease in insulin secretion. CONCLUSIONS: We demonstrated that some patients with type 1A diabetes experience hypoglycemic episodes before insulin therapy. Patients with early-stage type 1A diabetes with relatively low HbA1c or high UCPR have a risk of hypoglycemia. These findings may impact when and how insulin is introduced in the treatment of early-stage type 1A diabetes.

Four Japanese Patients with Congenital Nephrogenic Diabetes Insipidus due to the AVPR2 Mutations.

Almost 90% of nephrogenic diabetes insipidus (NDI) is caused by mutations in the arginine vasopressin receptor 2 gene (AVPR2) on the X chromosome. Herein, we reported clinical and biochemical parameters in four cases of three unrelated Japanese families and analyzed the status of the AVPR2. Two of the four patients had poor weight gain. However, in the male and female sibling cases, neither had poor weight gain while toddlers, but in the male sibling, episodes of recurrent fever, polyuria, and polydipsia led to the diagnosis of NDI at 4 years of age. Analysis of AVPR2 identified two nonsense mutations (c.299_300insA; p.K100KfsX91 and c.296G > A; p.W99X) and one missense mutation (c.316C > T; p.R106C). These mutations were previously reported. The patient with c.316C > T; p.R106C had milder symptoms consistent with previous reports. Of the familial cases, the sister was diagnosed as having NDI, but a skewed X-inactivation pattern in her peripheral blood lymphocytes was not identified. In conclusion, our study expands the spectrum of phenotypes and characterized mutations in AVPR2 in NDI.

Two siblings with congenital central hypothyroidism caused by a novel mutation in the IGSF1 gene.

Genetic defects in the immunoglobulin superfamily member 1(IGSF1) protein are the cause of congenital central hypothyroidism (C-CH). Here we report two Japanese siblings with C-CH due to a novel IGSF1 mutation. The youngest brother showed a failure to thrive, hypothermia, and neonatal icterus six days after birth. Further endocrine evaluations led to the diagnosis of C-CH. In addition, PRL deficiency was later detected. In contrast, the elder brother did not show symptoms of severe hypothyroidism during the neonatal period, but he had been followed up by doctors due to psychomotor developmental delays since the age of 1 yr. At the age of 3 yr, he had low thyroxine and PRL levels and was also diagnosed with C-CH. Because of the C-CH and PRL deficiency, an IGSF1 deficiency was suspected. Sequence analysis of the IGSF1 gene identified a novel hemizygous mutation of p.Trp1173GlyfsTer8 (NM_001170961.1:c.3517del) in both siblings. In conclusion, the phenotypic severity of C-CH is different, even in siblings. Importantly, an IGSF1 deficiency may result in severe hypothyroidism during the neonatal period.

A Japanese patient with congenital central hypothyroidism caused by a novel IGSF1 mutation.

BACKGROUND: IGSF1 abnormality causes diverse symptoms, including congenital central hypothyroidism (CCH), prolactin hyposecretion, testicular enlargement and delayed puberty. CASE PRESENTATION: Here, we report a case of a male patient who visited our hospital with a chief complaint of abdominal pain and short stature, in whom we identified a novel IGSF1 mutation. He was closely examined because of chronic constipation since infancy, persistent abdominal pain at 14 years of age and marked short stature (-4.7 standard deviation [SD] for normal Japanese boys). He was diagnosed with CCH. Decreased prolactin (PRL) secretion was also observed. IGSF1 analysis revealed a novel mutation at the splicing donor site (c.2065+1G>A) in intron 11. In silico analysis predicted this mutation to be a non-functional splice donor site. After thyroid hormone replacement, his thyroid function, constipation and growth rate improved. CONCLUSIONS: This is the first report of a patient in whom constipation and short stature led to a diagnosis of CCH with a novel IGSF1 mutation.

Clinical features and molecular basis of pseudohypoaldosteronism type 1.

Pseudohypoaldosteronism (PHA) type 1 is a disease showing mineralocorticoid resistance in the kidney and/or other mineralocorticoid target tissues. Patients with PHA1 present very high plasma aldosterone and renin levels, but they develop excessive salt wasting. There are three types of PHA1. The systemic form of PHA1 is inherited in an autosomal recessive manner and causes severe life-long salt loss in multiple target tissues, such as sweat glands, salivary glands, the colonic epithelium, and the lung. In the systemic form of PHA1, life-long salt supplementation is necessary. The second type is the renal form, where aldosterone resistance is shown only in the kidney, and its inheritance is autosomal dominant. In the renal form of PHA1, salt supplementation generally becomes unnecessary by 1-3 yr of age. The third type is the secondary PHA1, which is strongly associated with urinary tract infections and/or urinary tract malformations. This review summarizes the clinical features and molecular basis of PHA1. Understanding of its pathogenesis can be helpful for the early diagnosis and clinical care of affected children with PHA1.

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

BACKGROUND: 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. OBJECTIVE: Analyze the WFS1 and functional consequence of the patient WFS1 in vitro. RESULTS: The patient WFS1 contained a heterozygous 4 amino acid in-frame deletion (p.N325_I328del). Her mutant WFS1 increased GRP78 and ATF6α promoter activities in the absence of thapsigargin, indicating constitutive ER stress and nuclear factor of activated T-cell reporter activity, reflecting elevated cytosolic Ca2+ signals. Mutant transfection into cells reduced mRNA expression levels of sarcoplasmic/endoplasmic reticulum Ca2+ transport ATPase 2b (SERCA2b) compared with wild type. Because SERCA2b is required for ER and cytoplasmic Ca2+ homeostasis, decreased SERCA2b expression might affect ER Ca2+ efflux, causing cell apoptosis. CONCLUSION: A novel heterozygous mutation of WFS1 induced constitutive ER stress through ATF6α activation and ER Ca2+ efflux, resulting in cell apoptosis. These results provide new insights into the roles of WFS1 in UPR and mechanism of monogenic DM.

A Japanese Family with Central Hypothyroidism Caused by a Novel IGSF1 Mutation.

BACKGROUND: Hemizygous mutations in the immunoglobulin superfamily member 1 (IGSF1) gene have been demonstrated to cause congenital central hypothyroidism in males. This study reports a family with a novel mutation in the IGSF1 gene located on the long arm of the X chromosome. PATIENT FINDINGS: A two-month-old boy was diagnosed with central hypothyroidism because of prolonged jaundice. A thyrotropin-releasing hormone (TRH) stimulation test indicated dysfunction in both the hypothalamus and the pituitary gland, and prompted the IGSF1 gene to be analyzed. The patient had a novel nonsense variant, c.2713C>T (p.Q905X), in exon 14 of the IGSF1 gene. Studies of the family revealed that the patient's sister and mother were heterozygous carriers of the IGSF1 mutation. The patient's maternal uncle carried the same mutation as the proband but had no overt symptoms. The mother and uncle started levothyroxine supplementation because of subclinical hypothyroidism. SUMMARY: A novel mutation (c.2713C>T, p.Q905X) of the IGSF1 gene was identified that causes congenital central hypothyroidism in a Japanese family. The findings further expand the clinical heterogeneity of this entity.

Two Japanese patients with the renal form of pseudohypoaldosteronism type 1 caused by mutations of NR3C2.

Pseudohypoaldosteronism type 1 (PHA1) is a disease characterized by neonatal salt loss due to aldosterone resistance. Two types of PHA1 are known: an autosomal recessive systemic form and an autosomal dominant renal form. The cause of the renal form of PHA1 is heterozygous mutations in NR3C2, which encodes the mineralocorticoid receptor (MR). We encountered two female Japanese infants with the renal form of PHA1 and analyzed NR3C2. The two patients had poor weight gain, and one was developmentally delayed. Genetic analysis identified one novel mutation (c.492_493insTT, p.Met166LeufsX8) and one previously reported mutation (p.R861X). The two produced a premature stop codon, resulting in haploinsufficiency of the MR. In conclusion, genetic analysis of NR3C2 is useful for diagnosis and planning therapeutic strategies.

Spondyloepiphyseal dysplasia congenita caused by double heterozygous mutations in COL2A1.

Spondyloepiphyseal dysplasia congenita (SEDC) is a group of rare inherited chondrodysplasias characterized by short stature, abnormal epiphyses, and flattened vertebral bodies. SEDC is usually caused by substitution of glycine residue with another amino acid in the triple helical domains of alpha 1 chains, which consist of type II collagen (COL2A1). Herein, we describe a unique case of SEDC with mild coxa vara (SEDC-M) caused by double de novo COL2A1 mutations located on the same allele. One mutation, p.G504S, was previously described in patients with SEDC, whereas the other, p.G612A, was a novel mutation; both were located in the triple helical domain. Neither mutation was identified in the parents and appeared to be de novo. To the best of our knowledge, this is the first study involving a patient with a type II collagenopathy with two COL2A1 mutations on the same allele. The case was characterized by a more severe phenotype compared with previously reported cases involving a single p.G504S mutation, which may have been the result of the double mutation.

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.

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.