A case of diffuse congenital hyperinsulinism in which continuous glucose monitoring contributed to the choice of a treatment strategy following a subtotal pancreatectomy.

Patients with diffuse congenital hyperinsulinism (CHI) refractory to drug therapy require subtotal or near-total pancreatectomy. Although almost all patients develop diabetes postoperatively, the clinical course and timing of insulin therapy remain unclear. A 7-yr-old girl presented with recurrent hypoglycemia shortly after birth and a relatively elevated insulin level, which confirmed the diagnosis of CHI. Genetic analysis revealed compound heterozygous ATP-binding cassette, Subfamily C, Member 8 pathogenic variants and diffuse CHI was suspected. Because her condition was refractory to diazoxide and octreotide, she underwent a subtotal pancreatectomy at the age of 4 mo. The drug therapy was discontinued. Although an oral glucose tolerance test at the age of 2 yr showed hyperglycemia after loading, continuous glucose monitoring (CGM) revealed that her daily glucose trends were almost within the 70-180 mg/dL range, and mild hypoglycemia appeared during the daytime. After the age of 6 yr, CGM showed an elevation in glucose trends from midnight to early morning, suggesting that insulin secretion was attenuated and hepatic glucose production was insufficiently suppressed. Insulin therapy was initiated at the age of 7 yr. These results indicate that CGM can be useful for making treatment decisions.

A Male Japanese Patient with Temple Syndrome Complicated by Type 2 Diabetes Mellitus.

We herein present the case of a 21-year-old male Japanese diabetic patient with Temple syndrome, caused by maternal uniparental disomy of chromosome 14. The patient was overweight and had type 2 diabetes, dyslipidemia, metabolic dysfunction-associated steatotic liver disease, and microalbuminuria. He had an increased fat mass in the truncal region and a decreased lean mass throughout the body. This may lead to insulin resistance due to the absence of delta-like homolog 1 (DLK1) and retrotransposon gag-like 1 (RTL1). The patient had experienced social withdrawal at home (hikikomori in Japanese), had poorly controlled type 2 diabetes, and was overweight despite receiving diet therapy and oral hypoglycemic agents.

International Guidelines for the Diagnosis and Management of Hyperinsulinism.

Hyperinsulinism (HI) due to dysregulation of pancreatic beta-cell insulin secretion is the most common and most severe cause of persistent hypoglycemia in infants and children. In the 65 years since HI in children was first described, there has been a dramatic advancement in the diagnostic tools available, including new genetic techniques and novel radiologic imaging for focal HI, however; there have been almost no new therapeutic modalities since the development of diazoxide. Recent advances in neonatal research and genetics have improved our understanding of the pathophysiology of both transient and persistent forms of neonatal hyperinsulinism. Rapid turnaround of genetic test results combined with advanced radiologic imaging can permit identification and localization of surgically-curable focal lesions in a large proportion of children with congenital forms of HI, but are only available in certain centers in 'developed' countries. Diazoxide, the only drug currently approved for treating HI, was recently designated as an "essential medicine" by the World Health Organization but has been approved in only 16% of Latin American countries and remains unavailable in many under-developed areas of the world. Novel treatments for HI are emerging, but they await completion of safety and efficacy trials before being considered for clinical use. This international consensus statement on diagnosis and management of HI was developed in order to assist specialists, general pediatricians, and neonatologists in early recognition and treatment of HI with the ultimate aim of reducing the prevalence of brain injury caused by hypoglycemia. A previous statement on diagnosis and management of HI in Japan was published in 2017. The current document provides an updated guideline for management of infants and children with HI and includes potential accommodations for less-developed regions of the world where resources may be limited.

Oculofaciocardiodental syndrome caused by a novel BCOR variant.

Oculofaciocardiodental syndrome is caused by variants in the BCL6 corepressor (BCOR) gene. We identified a novel heterozygous frameshift variant, NM_001123385.2(BCOR):c.2326del, that arose de novo in a Japanese girl with characteristic facial features, congenital heart disease, bilateral syndactyly of toes 2 and 3, congenital cataracts, dental abnormalities, and mild intellectual disability. Reports of BCOR variants are rare, and further case accumulation is warranted.

Glucokinase maturity-onset diabetes of the young as a mimicker of stress hyperglycemia: a case report.

Febrile seizures are frequently accompanied by stress-induced hyperglycemia. Herein, we report the case of a 1.5-yr-old girl with hyperglycemia during febrile seizures who was subsequently diagnosed with glucokinase (GCK) maturity-onset diabetes of the young (MODY), considering its distinction from stress hyperglycemia. Following the development of febrile seizures owing to adenovirus infection, the patient presented a casual blood glucose level was 185 mg/dL. She had a multigenerational family history of diabetes and a hemoglobin A1c (HbA1c) level of 6.4%. Owing to the persistent glucose intolerance until the age of 5 years, genetic testing was performed, which revealed a heterozygous mutation in GCK, and the patient was diagnosed with GCK-MODY. Precise diagnosis of GCK-MODY individuals is important to avoid administering unnecessary antidiabetic medications. Even during hyperglycemia under stress, multigenerational diabetes and mildly elevated HbA1c levels can suggest GCK-MODY.

Increased frequency of central precocious puberty during the coronavirus disease (COVID-19) pandemic at a single center in the Osaka Metropolitan Area of Japan.

As environmental factors are known to affect the timing of puberty, self-isolation during the coronavirus disease (COVID-19) pandemic may affect the incidence of central precocious puberty (CPP). This study aimed to evaluate the frequency of CPP during the COVID-19 pandemic at a single center in the Osaka metropolitan area of Japan. We retrospectively analyzed the annual frequency of CPP occurrence before and after the first declaration of COVID-19 state of emergency in Japan at our hospital. We performed an interrupted time-series analysis to investigate the frequency of patients with CPP at our hospital from 2016 to 2021. There was a significant increase in the frequency of patients with CPP before and after the state of emergency declaration, both overall and among females. However, there was no significant increase in the number of males. There were no significant differences in the clinical, auxological, and endocrinological features between those diagnosed before and after the state of emergency. Overall, the frequency of CPP significantly increased during the COVID-19 pandemic at a single center in the Osaka metropolitan area of Japan.

Targeted gene panel analysis of Japanese patients with maturity-onset diabetes of the young-like diabetes mellitus: Roles of inactivating variants in the ABCC8 and insulin resistance genes.

AIMS/INTRODUCTION: To investigate the genetic background of Japanese patients with suspected maturity-onset diabetes of the young (MODY). MATERIALS AND METHODS: On 340 proband patients referred from across Japan, genomic variants were analyzed using a targeted multigene panel analysis combined with the multiplex ligation probe amplification (MLPA) analysis, mitochondrial m.3243A > G analysis and methylation-specific polymerase chain reaction of the imprinted 6q24 locus. Pathogenic/likely pathogenic variants were listed according to the 2015 American College of Medical Genetics and Genomics and the Association for Molecular Pathology criteria. Additionally, variants with a population frequency <0.001 and Combined Annotation Dependent Depletion score >20 (CS >20) were listed as rare variants of uncertain significance-CS >20. RESULTS: A total of 157 pathogenic/likely pathogenic variants and 44 rare variants of uncertain significance-CS >20 were identified. In the pathogenic/likely pathogenic variants, alterations in the GCK gene were the most common (82, 52.2%) followed by HNF1A (29, 18.5%), HNF4A (13, 8.3%) and HNF1B (13, 8.3%). One patient was a 29.5% mosaic with a truncating INSR variant. In the rare variants of uncertain significance-CS >20, 20 (45.5%) were in the genes coding for the adenosine triphosphate-sensitive potassium channel, KCNJ11 or ABCC8, and four were in the genes of the insulin-signaling pathway, INSR and PIK3R1. Four variants in ABCC8 were previously reported in patients with congenital hyperinsulinism, suggesting the inactivating nature of these variants, and at least two of our patients had a history of congenital hyperinsulinism evolving into diabetes. In two patients with INSR or PIK3R1 variants, insulin resistance was evident at diagnosis. CONCLUSIONS: Causative genomic variants could be identified in at least 46.2% of clinically suspected MODY patients. ABCC8-MODY with inactivating variants could represent a distinct category of MODY. Genes of insulin resistance should be included in the sequencing panel for MODY.

Possible critical region associated with late-onset spasms in 17p13.1-p13.2 microdeletion syndrome: a report of two new cases and review of the literature.

17p13.1-2 microdeletion syndrome is a congenital anomaly syndrome with characteristic facial features and multiple malformations. The prevalence of epilepsy with 17p13.1-2 microdeletion is low, with only one case reported for late-onset spasms. Late-onset spasms is one of the rare epilepsy syndromes and one of the developmental epileptic encephalopathies requiring urgent treatment. We experienced two cases of 17p13.1-2 microdeletion syndrome, one of which presented with epileptic spasms in cluster at 18 months of age. EEG showed symmetrical hypsarrhythmia during interictal periods and a paroxysmal fast wave superimposed on widespread slow waves during seizures, leading to the diagnosis of late-onset spasms. Another case had no epilepsy. Comparing the extent of deletion in the two cases with that of previous reports, the involvement of the USP6 gene was suspected. However, the accumulation of additional case reports is needed to confirm the genetic involvement in late-onset spasms.

New classification and diagnostic criteria for insulin resistance syndrome.

This report of a working group established by the Japan Diabetes Society proposes a new classification and diagnostic criteria for insulin resistance syndrome. Insulin resistance syndrome is defined as a condition characterized by severe attenuation of insulin action due to functional impairment of the insulin receptor or its downstream signaling molecules. This syndrome is classified into two types: genetic insulin resistance syndrome, caused by gene abnormalities, and type B insulin resistance syndrome, caused by autoantibodies to the insulin receptor. Genetic insulin resistance syndrome includes type A insulin resistance as well as Donohue and Rabson-Mendenhall syndromes, all of which are caused by abnormalities of the insulin receptor gene; conditions such as SHORT syndrome caused by abnormalities of PIK3R1, which encodes a regulatory subunit of phosphatidylinositol 3-kinase; conditions caused by abnormalities of AKT2, TBC1D4, or PRKCE; and conditions in which a causative gene has not yet been identified. Type B insulin resistance syndrome is characterized by severe impairment of insulin action due to the presence of insulin receptor autoantibodies. Cases in which hypoglycemia alone is induced by autoantibodies that stimulate insulin receptor were not included in Type B insulin resistance syndrome.

Efficacy and Safety of Once-Weekly Somatrogon Compared with Once-Daily Somatropin (Genotropin®) in Japanese Children with Pediatric Growth Hormone Deficiency: Results from a Randomized Phase 3 Study.

INTRODUCTION: Somatrogon is a long-acting recombinant human growth hormone being developed as a once-weekly treatment for children with growth hormone deficiency (GHD). The objective of this phase 3 study (NCT03874013) was to compare the efficacy and safety of once-weekly somatrogon with once-daily Genotropin in Japanese children with GHD. METHODS: In this open-label, randomized, active-controlled study, 44 prepubertal Japanese children with GHD (boys: 3 to <11 years; girls: 3 to <10 years) were randomized 1:1 to receive once-weekly somatrogon or once-daily Genotropin (0.025 mg/kg/day) for 12 months. Dose escalation for somatrogon-treated subjects occurred in the first 6 weeks (0.25, 0.48, and 0.66 mg/kg/week; 2 weeks each) with the remaining 46 weeks at a dose of 0.66 mg/kg/week. The study's primary endpoint was annualized height velocity (HV) at 12 months. RESULTS: Baseline characteristics were similar between treatment groups. Compared with Genotropin-treated subjects, somatrogon-treated subjects had higher least-squares mean HV at 12 months (9.65 cm/year vs. 7.87 cm/year). Once-weekly somatrogon was concluded as being comparable to once-daily Genotropin as the mean treatment difference (somatrogon-Genotropin) in HV was +1.79 cm/year (95% confidence interval, 0.97-2.61), which was greater than the preestablished margin (-1.8 cm/year). For both treatment groups, most adverse events were mild to moderate in severity and a similar proportion of subjects reported injection-site pain, although the somatrogon group reported more painful injections. CONCLUSION: In prepubertal Japanese children with GHD, once-weekly somatrogon was comparable to once-daily Genotropin in terms of annualized (12-month) HV. Both treatments had similar safety and tolerability profiles.

Identification of clinical factors related to antibody-mediated immune response to the subfornical organ.

OBJECTIVE: We recently reported cases of adipsic hypernatremia caused by autoantibodies against the subfornical organ in patients with hypothalamic-pituitary lesions. This study aimed to clarify the clinical features of newly identified patients with adipsic hypernatremia whose sera displayed immunoreactivity to the mouse subfornical organ. DESIGN: Observational cohort study of patients diagnosed with adipsic hypernatremia in Japan, United States, and Europe. METHODS: The study included 22 patients with adipsic hypernatremia but without overt structural changes in the hypothalamic-pituitary region and congenital disease. Antibody response to the mouse subfornical organ was determined using immunohistochemistry. The clinical characteristics were compared between the patients with positive and negative antibody responses. RESULTS: Antibody response to the mouse subfornical organ was detected in the sera of 16 patients (72.7%, female/male ratio, 1:1, 12 pediatric and 4 adult patients). The prolactin levels at the time of diagnosis were significantly higher in patients with positive subfornical organ (SFO) immunoreactivity than in those with negative SFO immunoreactivity (58.9 ± 33.5 vs. 22.9 ± 13.9 ng/ml, p < .05). Hypothalamic disorders were found in 37.5% of the patients with positive SFO immunoreactivity. Moreover, six patients were diagnosed with rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation/neural tumor syndrome after the diagnosis of adipsic hypernatremia. Plasma renin activity levels were significantly higher in patients with serum immunoreactivity to the Nax channel. CONCLUSIONS: The patients with serum immunoreactivity to the SFO had higher prolactin levels and hypothalamic disorders compared to those without the immunoreactivity. The clinical characteristics of patients with serum immunoreactivity to the subfornical organ included higher prolactin levels and hypothalamic disorders, which were frequently associated with central hypothyroidism and the presence of retroperitoneal tumors.

New classification and diagnostic criteria for insulin resistance syndrome.

This report of a working group established by the Japan Diabetes Society proposes a new classification and diagnostic criteria for insulin resistance syndrome. Insulin resistance syndrome is defined as a condition characterized by severe attenuation of insulin action due to functional impairment of the insulin receptor or its downstream signaling molecules. This syndrome is classified into two types: genetic insulin resistance syndrome, caused by gene abnormalities, and type B insulin resistance syndrome, caused by autoantibodies to the insulin receptor. Genetic insulin resistance syndrome includes type A insulin resistance as well as Donohue and Rabson-Mendenhall syndromes, all of which are caused by abnormalities of the insulin receptor gene; conditions such as SHORT syndrome caused by abnormalities of PIK3R1, which encodes a regulatory subunit of phosphatidylinositol 3-kinase; conditions caused by abnormalities of AKT2, TBC1D4, or PRKCE; and conditions in which a causative gene has not yet been identified. Type B insulin resistance syndrome is characterized by severe impairment of insulin action due to the presence of insulin receptor autoantibodies. Cases in which hypoglycemia alone is induced by autoantibodies that stimulate insulin receptor were not included in Type B insulin resistance syndrome.

A 36-year-old Man with Repeated Short-term Transient Hyperammonemia and Impaired Consciousness with a Confirmed Carbamoyl Phosphate Synthase 1 Gene Monoallelic Mutation.

A 36-year-old man experienced severely impaired consciousness twice after drinking because of hyperammonemia. No abnormal blood tests were found other than ammonia levels. However, magnetic resonance imaging (MRI) showed atrophy of the brain parenchyma. One the second occasion, the patient suffered severe impairment of consciousness, and because of seizures and glossoptosis, mechanical ventilation was started. Urea cycle disorders (UCDs) were assumed to be involved. Genetic testing revealed a monoallelic mutation of the carbamoyl phosphate synthase 1 (CPS1) gene. When transient hyperammonemia of unknown cause occurs repeatedly in adults, an active investigation for UCDs should be conducted.

Accelerated pubertal onset in short children with delayed bone age.

OBJECTIVES: Constitutional delay of growth (CDG) is usually associated with a delay in pubertal onset (CDGP) and a catch-up growth after puberty. Some individuals, however, have earlier-than-expected pubertal onset resulting in a shorter adult height. We investigated the current incidence of such individuals and that of 30 years ago. METHODS: The study subjects are 1,312 consecutive Japanese children referred to Osaka City General Hospital (OCGH) for short stature during 2010-2018, and a cohort of 11,256 individuals in the Ogi Growth Research (OGR, 1979-1992). Individuals with the height standard deviation score <-1.0, the bone age (BA)/chronological age (CA) ratio <0.8 at first visits, and without other identifiable causes of short stature were extracted from the record of OCGH. Similarly, individuals meeting the height and bone age criteria were extracted from the OGR record. The pubertal growth onset was auxologically determined as the upward shift from the prepubertal growth curve fitted to a quadratic function. Earlier-than-expected onset was defined as the onset earlier than the population average +1 year. RESULTS: From the OCGH cohort, 55 children (38 boys, 17 girls) met the criteria, and earlier-than-expected onset was observed in 34.2% of boys and 29.4% of girls. In the 73 short individuals with delayed bone age in the OGR cohort, earlier-than-expected onset was less common (13.0% for boys and 14.8% for girls). There was no significant association between the timing of pubertal growth onset and the BA/CA ratio, IGF-1, and midparental height. CONCLUSIONS: Earlier-than-expected pubertal growth onset is common in CDG and possibly increasing.

Mutational and clinical spectrum of Japanese patients with hereditary hemorrhagic telangiectasia.

BACKGROUND: Hereditary hemorrhagic telangiectasia (HHT) is a dominantly inherited vascular disorder characterized by recurrent epistaxis, skin/mucocutaneous telangiectasia, and organ/visceral arteriovenous malformations (AVM). HHT is mostly caused by mutations either in the ENG or ACVRL1 genes, and there are regional differences in the breakdown of causative genes. The clinical presentation is also variable between populations suggesting the influence of environmental or genetic backgrounds. In this study, we report the largest series of mutational and clinical analyses for East Asians. METHODS: Using DNAs derived from peripheral blood leukocytes of 281 Japanese HHT patients from 150 families, all exons and exon-intron boundaries of the ENG, ACVRL1, and SMAD4 genes were sequenced either by Sanger sequencing or by the next-generation sequencing. Deletions/amplifications were analyzed by the multiplex ligation-dependent probe amplification analyses. Clinical information was obtained by chart review. RESULTS: In total, 80 and 59 pathogenic/likely pathogenic variants were identified in the ENG and ACVRL1 genes, respectively. No pathogenic variants were identified in the SMAD4 gene. In the ENG gene, the majority (60/80) of the pathogenic variants were private mutations unique to a single family, and the variants were widely distributed without any distinct hot spots. In the ACVRL1 gene, the variants were more commonly found in exons 5-10 which encompasses the serine/threonine kinase domain. Of these, 25/59 variants were unique to a single family while those in exons 8-10 tended to be shared by multiple (2-7) families. Pulmonary and cerebral AVMs were more commonly found in ENG-HHT (69.1 vs. 14.4%, 34.0 vs. 5.2%) while hepatic AVM was more common in ACVRL1-HHT (31.5 vs. 73.2%). Notable differences include an increased incidence of cerebral (34.0% in ENG-HHT and 5.2% in ACVRL1-HHT), spinal (2.5% in ENG-HHT and 1.0% in ACVL1-HHT), and gastric AVM (13.0% in ENG-HHT, 26.8% in ACVRL1-HHT) in our cohort. Intrafamilial phenotypic heterogeneity not related to the age of examination was observed in 71.4% and 24.1% of ENG- and ACVRL1-HHT, respectively. CONCLUSIONS: In a large Japanese cohort, ENG-HHT was 1.35 times more common than ACVRL1-HHT. The phenotypic presentations were similar to the previous reports although the cerebral, spinal, and gastric AVMs were more common.

Case Report: A Difficult-to-Diagnose Case of Hyperinsulinemic Hypoglycemia Surgically Treated After Developing Acute Pancreatitis.

The patient is a 28-year-old Japanese man diagnosed with severe congenital hyperinsulinemic-hypoglycemia six months after birth. Clinical records revealed no imaging evidence of pancreatic tumor at the time of diagnosis. Subsequently, he had developmental disorders and epilepsy caused by recurrent hypoglycemic attacks. The patient's hypoglycemia improved with oral diazoxide. However, he developed necrotizing acute pancreatitis at 28 years of age, thought to be due to diazoxide. Discontinuation of diazoxide caused persistent hypoglycemia, requiring continuous glucose supplementation by tube feeding and total parenteral nutrition. A selective arterial secretagogue injection test revealed diffuse pancreatic hypersecretion of insulin. He underwent subtotal distal (72%) pancreatectomy and splenectomy. There was no intraoperative visible pancreatic tumor. His hypoglycemia improved after the surgical procedure. The histopathological study revealed a high density of islets of Langerhans in the pancreatic body and tail. There were large islets of Langerhans and multiple neuroendocrine cell nests in the whole pancreas. Nests of neuroendocrine cells were also detected in lymph nodes. The pathological diagnosis was grade 1 neuroendocrine tumor (microinsulinomas) with lymph node metastases. This patient is a difficult-to-diagnose case of hyperinsulinemic hypoglycemia surgically treated after developing acute pancreatitis. We believe this is a unique case of microinsulinomas with lymph metastases diagnosed and treated as congenital hyperinsulinemic hypoglycemia for almost 28 years.

Longitudinal Glycaemic Profiles during Remission in 6q24-Related Transient Neonatal Diabetes Mellitus.

INTRODUCTION: Transient neonatal diabetes mellitus (TNDM) is a rare condition that is characterized by the presence of diabetes mellitus during the first 6 months of life and remission by 18 months of age. It usually relapses at a median age of 14 years. Hyperinsulinaemic hypoglycaemia is a relatively common complication during remission. Although ß-cell function is reported to be impaired at relapse, the clinical course of glycaemic profiles during remission in patients with TNDM remains largely unknown. CASE PRESENTATION: Longitudinal glycaemic profiles were investigated annually from remission (185 days) to relapse (14.5 years) in a patient with TNDM due to paternal 6q24 duplication using the oral glucose tolerance test (glucose intake: 1.75 g/kg to a maximum of 75 g). The patient's ß-cell function and insulin sensitivity were assessed by calculating the insulinogenic index, homeostasis model assessment of ß-cell function (HOMA-ß), homeostasis model assessment of insulin resistance (HOMA-IR), quantitative insulin sensitivity check index, and Matsuda index. Early insulin response to glucose intake was impaired throughout remission, whereas fasting insulin and ß-cell function by HOMA-ß gradually increased in the first few years since remission, followed by a gradual decline in function. In contrast, HOMA-IR fluctuated and peaked at 6.5 years of age. CONCLUSION: This is the first report of annual longitudinal glycaemic profiles in a patient with 6q24-related TNDM during remission. We identified fluctuations in ß-cell function and insulin resistance during remission.

A nationwide questionnaire survey targeting Japanese pediatric endocrinologists regarding transitional care in childhood, adolescent, and young adult cancer survivors.

Existing guidelines recommend long-term follow-up of childhood cancer survivors (CCS). However, in Japan, transitional care for CCS has not been established. To ascertain the current status in Japan, and to cultivate a better understanding, a questionnaire survey was conducted on transitional care in CCS, and adolescent and young adult (AYA) cancer survivors. Questionnaires were distributed to 183 councilors (137 institutions) of the Japanese Society for Pediatric Endocrinology. A total of 131 responses, representative of 174 councilors, were obtained. The response rate was 95%. Among the respondents, 91% had experience in medical care for cancer patients, while 63% had experience in transitional care; however, the number of patients referred to adult clinics was small. Further, 89% acknowledged the availability of adult endocrinologists who were willing to accept these patients; although their numbers were insufficient. Pediatric endocrinologists highlighted difficulties in medical examinations concerning infertility, obesity, pregnancy/delivery, and gonadal dysfunction, in that order. Staff and time shortages were listed as some of the challenges faced by medical staff, while multisystem morbidity was listed for patients. This nationwide questionnaire survey revealed that Japanese pediatric endocrinologists require cooperation between related departments and collaborative infrastructure to develop transitional care for cancer survivors.

Clinical characteristics of insulin resistance syndromes: A nationwide survey in Japan.

AIMS/INTRODUCTION: Insulin resistance syndrome (IRS) of type A or B is triggered by gene abnormalities of or autoantibodies to the insulin receptor, respectively. Rabson-Mendenhall/Donohue syndrome is also caused by defects of the insulin receptor gene (INSR), but is more serious than type A IRS. Here, we carried out a nationwide survey of these syndromes in Japan. MATERIALS AND METHODS: We sent questionnaires to a total of 1,957 academic councilors or responsible individuals at certified facilities of the Japan Diabetes Society, as well as at the department pediatrics or neonatology in medical centers with >300 beds. RESULTS: We received 904 responses with information on 23, 30 and 10 cases of type A or B IRS and Rabson-Mendenhall/Donohue syndrome, respectively. Eight cases with type A IRS-like clinical features, but without an abnormality of INSR, were tentatively designated type X IRS, with five of these cases testing positive for PIK3R1 mutations. Fasting serum insulin levels at diagnosis (mean ± standard deviation) were 132.0 ± 112.4, 1122.1 ± 3292.5, 2895.5 ± 3181.5 and 145.0 ± 141.4 µU/mL for type A IRS, type B IRS, Rabson-Mendenhall/Donohue syndrome and type X IRS, respectively. Type A and type X IRS, as well as Rabson-Mendenhall/Donohue syndrome were associated with low birthweight. Type B IRS was diagnosed most frequently in older individuals, and was often associated with concurrent autoimmune conditions and hypoglycemia. CONCLUSIONS: Information yielded by this first nationwide survey should provide epidemiological insight into these rare conditions and inform better healthcare for affected patients.