Noninsulinoma pancreatogenous hypoglycemia: a novel syndrome of hyperinsulinemic hypoglycemia in adults independent of mutations in Kir6.2 and SUR1 genes.

In adults, endogenous hyperinsulinemic hypoglycemia is almost invariably due to insulinoma. In these patients with insulinoma, neuroglycopenic episodes exclusively after meal ingestion and negative 72-h fasts are extraordinarily rare. We describe five adults with neuroglycopenic episodes from hyperinsulinemic hypoglycemia within 4 h of meal ingestion and negative 72-h fasts. Each had negative transabdominal ultrasonography, spiral computed tomographic scanning, and celiac axis angiography of the pancreas. However, all showed positive selective arterial calcium stimulation tests indicative of pancreatic beta-cell hyperfunction. At pancreatic exploration, no insulinoma was detected by intraoperative ultrasonography and complete mobilization and palpation of the pancreas. Moreover, the resected pancreata showed islet hypertrophy and nesidioblastosis, but no insulinoma. No definite disease-causing mutation was detected in Kir6.2 and SUR1 genes, which encode the subunits of the pancreatic ATP-sensitive potassium channel responsible for glucose-induced insulin secretion. Four patients who underwent gradient-guided partial pancreatectomy have been free of hypoglycemic symptoms for up to 3 yr follow-up; the other, who underwent a limited distal pancreatectomy, has had brief recurrence of symptoms. The unique clinical features and responses to dynamic testing in these adults with hyperinsulinemic hypoglycemia in the absence of insulinoma may constitute a new syndrome of postprandial hypoglycemia from diffuse beta-cell hyperfunction.     

Paradoxal growth hormone and cortisol response to hypoglycemia caused by endogenous hyperinsulinemia: a case report

Growth hormone (GH) together with cortisol are two important counter-regulatory hormones maintaining normal glycemia. Hyperinsulinemic hypoglycemia is a disorder of this counter-regulation described in neonates. We report here a rare case of reversible dissociated hypopituitarism secondary to an insulinoma in a 38-year-old man referred for investigation of hypoglycemic episodes. Hormonal investigations were in favour of dissociated anterior pituitary failure, with growth hormone and corticotroph deficiency. The hypothalamic-pituitary MRI was normal. The fasting test argued in favour of a hyperinsulinemic hypoglycemia. The abdominal scan and the endoscopic ultrasound showed a mass within the tail of the pancreas. Distal pancreatectomy was performed. Histology disclosed an insulinoma. On follow-up, no hypoglycemic episodes recurred and cortisol and GH response to induced hypoglycemia was normal. Our clinical case shows that hyperinsulinemia and hypoglycemia in patients with insulinoma can give rise to functional growth hormone and corticotrophin deficiency. The pathophysiological mechanism of this defective counter-regulation remains to be clarified; some studies suggest it could be related to hyperinsulinemia-induced decreased in CRF secretion and GHRH pulse.     

Adult-onset diffuse nesidioblastosis causing hypoglycemia

We report the case of a 32-year-old male with adult-onset diffuse nesidioblastosis causing hypoglycemia. Under the tentative diagnosis of insulinoma, localization procedures were carried out but no tumor was found. The presence of an insulinoma in the tail of the pancreas was suggested by selective intra-arterial calcium stimulation with hepatic venous sampling (ASVS). A distal pancreatectomy was performed under the assumed diagnosis of insulinoma in the tail based upon the ASVS. Diffuse nesidioblastosis was diagnosed by histopathological evaluation. During the post-operative course, the patient’s glucose and insulin levels were well controlled and uneventful without any medications or insulin for 7 months.     

A rare case of adult-onset nesidioblastosis treated successfully with diazoxide

A 54-year-old man was admitted to our hospital for evaluation of hypoglycemia. He had frequent episodes of loss of concentration before dinner. The ratio of IRI to plasma glucose (PG) was 0.8-1.0. Abdominal CT revealed no pancreatic tumor, and angiography of splenic artery showed no definite tumor stain within the pancreas. Based on the results of selective arterial calcium stimulation and hepatic venous sampling (ASVS), the provisional diagnosis was a small insulinoma in the pancreatic body. The patient underwent subtotal distal pancreatectomy. However, histopathological and immunohistochemical examinations of the resected tissue showed hypertrophy of islets of Langerhans islands and beta cells around pancreatic ducts. The final diagnosis was adult-onset nesidioblastosis. Postoperatively, the patient continued to exhibit hyperinsulinemia and nighttime hypoglycemia. Octreotide, voglibose and diet therapies failed to improve the nocturnal hypoglycemia. However, treatment with diazoxide at a starting dose of 200 mg/day resulted in immediate amelioration of nocturnal hypoglycemia. This is the first Japanese adult case of nesidioblastosis treated successfully with diazoxide. This case report suggests that diazoxide may be effective for adult-onset nesidioblastosis in a manner similar to that described for pediatric cases.     

Hyperinsulinemic hypoglycemia due to diffuse nesidioblastosis in adults： A case report

Persistent hyperinsulinemic hypoglycemia is caused most commonly by an insulinoma in adults or by nesidioblastosis in neonates. In adults, nesidioblastosis is a rare disorder characterized by diffuse or disseminated proliferation of islet cells. We recently encountered a case of nesidioblastosis in an adult. A 71-year-old man was admitted due to intermittent general weakness, abdominal pain, and mild dyspnea. The patient underwent a subtotal gastrectomy for a gastric adenocarcinoma two years ago. After 5 d of admission, the patient showed symptoms of cold sweating, chilling, and hypotension 30 min after eating. Thereafter, he frequently showed similar symptoms accounting for hypoglycemia regardless of food consumption. Laboratory findings revealed a low fasting blood glucose level （25 mg/dL）, and a high insulin level （47 μIU/mL）. Selective intra-arterial calcium stimulation with hepatic venous sampling （ASVS） was performed to localize a mass and revealed an increased insulin level about fourfold that of the normal fasting level at 60 s in the splenic artery, which suggested the presence of an insulinoma in the tail of pancreas. A distal pancreatectomy was performed. Neither intraoperative exploration nor a frozen biopsy specimen detected any mass-forming lesion. On the histological examination, many of the islets were enlarged and irregularly shaped in all specimens, the arrangement of which was a Iobulated islet pattern. Cytologically, a considerable subpopulation of endocrine cells showed enlarged and hyperchromatic nuclei. By immunohistochemistry, the cells were identified as p-cells. These clinical, radiological, microscopic and immuno-histochemical findings are consistent with diffuse nesidioblastosis in adults.     

Insulin responses to selective arterial calcium infusion under hyperinsulinemic euglycemic glucose clamps: case studies in adult nesidioblastosis and childhood insulinoma

Selective arterial calcium stimulation and hepatic venous sampling (ASVS) for insulin secretion is used as a diagnostic procedure in patients with insulinomas or adult nesidioblastosis. In some of those patients, severe hypoglycemia requiring urgent glucose administration occurs during the procedure. Such glucose administration, however, may affect the results and damage the validity of the test. We report two cases of hyperinsulinemic hypoglycemia, in which ASVS tests were successfully performed under hyperinsulinemic euglycemic glucose clamps. A 40-year-old male with nesidioblastosis developed continual severe hypoglycemia several years after a Billroth II-Braun gastrectomy, and continuous glucose infusion could not be stopped even during ASVS tests. A 9-year-old girl with an insulinoma that showed atypical hypovascularity on imaging examinations had ASVS tests under a glucose clamp for safety. Hyperinsulinemic (approximately 100 microU/ml) euglycemic (approximately 90 mg/dl) clamps were achieved by an artificial endocrine pancreas. The insulin analogue lispro was utilized for clamps and endogenous insulin was measured with an assay that does not cross-react with the analogue. Diagnostically significant responses (more than twofold) of insulin secretion were observed under hyperinsulinemic clamps in both cases. The use of the hyperinsulinemic glucose clamp technique during the ASVS test should be considered for maintaining the safety of some hypoglycemic patients.     

Nesidioblastosis associated with hyperinsulinemic hypoglycemia in adults: review of the literature

Nesidioblastosis is a term that was first introduced by Laidlaw in 1938 to define the diffuse proliferation of pancreatic islet cells budding from ductal epithelium. First described in neonates, it is widely recognized to be the primary cause of persistent hyperinsulinemic hypoglycemia in infants. In adults, insulinoma accounts for most cases of hyperinsulinemic hypoglycemia. Adult-onset nesidioblastosis associated with hyperinsulinemic hypoglycemia is a very rare entity, representing 0.5-5% of cases of organic hyperinsulinemia. Since 1981, when Harness et al. reported the first series of adult nesidioblastosis causing hypoglycemia, only 71 cases have been published. This article provides a guide for the diagnosis of organic hyperinsulinism and indicates when nesidioblastosis should be suspected. New diagnostic methods and treatment options for this rare disease are proposed. We also present a review of all reported cases of adult nesidioblastosis in the last 22 years.     

Hyperinsulinemic hypoglycemia due to adult nesidioblastosis in insulin-dependent diabetes

INTRODUCTION Persistent hyperinsulinemic hypoglycemia (PHH) caused by functionally defectice β-cells in the setting of anesidioblastosis is the most common pathological substrate in newborns, whereas in adults, PHH is usually caused by solitary insulinomas[1-3]. Several genetic abnormalities were identified as the causes of PHH in infancy. The most important mutations are in the β-cell sulfonylurea receptor (SUR1) gene and encoding proteins composing the ATP- sensitive potassium ch…     

Insulinoma: Selective arterial calcium injection performed to confirm localization and complete resection

A case of insulinoma is reported in a patient in whom selective arterial calcium injection (SACI) tests were performed both to confirm tumor localization before surgery and to confirm complete tumor removal during surgery. An 18-year-old woman with hypoglycemic episodes was diagnosed with an insulinoma in the pancreatic body demonstrated by celiac arteriography. In a preoperative SACI test, calcium was injected into the splenic artery (SpA), gastroduodenal artery (GDA), and superior mesenteric artery (SMA). Serum immunoreactive insulin (IRI) and proinsulin levels were measured in hepatic venous samples. IRI was markedly increased after the injection of calcium into the GDA and SMA, while there was no response in IRI levels when calcium was injected into the SpA. Therefore, no occult insulinoma was revealed in the distal area fed by the SpA, although the presence of insulinoma was uncertain in the proximal pancreas. In the intraoperative SACI test, calcium was injected into the celiac artery. Insulin (determined by enzyme immunoassay) and proinsulin levels were measured in portal venous samples before and after resection of the tumor. After resection, these levels decreased in response to the calcium stimuli, confirming complete removal of the insulinoma. The SACI test was helpful to localize the insulinoma and was useful to confirm the complete removal of the tumor.     

Successful treatment of insulinoma by a single daily dose of octreotide in two elderly female patients

We report two cases of insulinoma in advanced age patients considered unsuitable for surgery, in whom single daily doses of octreotide successfully improved hypoglycemia and hyperinsulinemia. The biological half-life of octreotide is about 100 min, hence it is customary to use two or three administrations per day to prevent hypoglycemia in insulinoma patients. The first case was a 76-year-old woman who presented with hyperinsulinemic hypoglycemia. Computed tomography (CT) and magnetic resonance imaging did not identify a tumor in the pancreas but a 1.5-cm tumor was found in the pancreatic body on abdominal angiography and selective arterial calcium stimulation and hepatic venous sampling (ASVS) were compatible with insulinoma. The patient refused surgery, but was successfully treated with octreotide at 50 microg subcutaneous injection once daily. Since the treatment was started (1 year), she has not suffered hypoglycemia. Case 2 was an 85-year-old woman who presented with hyperinsulinemic hypoglycemia. CT identified a 1.5-cm tumor in the pancreatic uncus, but she was considered unsuitable for surgery due to advanced age, obesity and cardiopulmonary dysfunction. Octreotide at 100 microg subcutaneous injection once daily prevented further hypoglycemic attacks, but two months later, postprandial plasma glucose was elevated. Octreotide was gradually reduced to 50 microg once daily. Three years have passed since the treatment without any hypoglycemic attack. Successful treatment with octreotide once daily could be due to old-age-related slow metabolism and could be potentially considered as the treatment of choice for elderly patients with insulinoma especially those considered unsuitable for surgery.     

A case of hyperinsulinemia of undetermined origin, successfully treated with long-acting octreotide

Major causes of fasting hypoglycemia in adults are insulinoma, factitious hypoglycemia and nesidioblastosis. The primary treatment for insulinoma is surgical removal of the tumor, but there are cases with hyperinsulinemia that cannot undergo surgery. Somatostatin analogue is one of the treatments used in such cases of insulinoma or persistent hyperinsulinemic hypoglycemia. We report here a patient who had undetermined hyperinsulinemia and was successfully treated with a long-acting somatostatin analogue, which had recently become available. The patient, a 72-year-old female, who had previously been diagnosed as insulinoma and undergone partial pancreatectomy, was admitted complaining of the recurrence of hypoglycemic attacks after an interval of ten years. On admission, hypoglycemia (42 mg/dl), hyperinsulinemia (IRI: 79.3 microU/m) and low HbA1c (3.6%) were present. In 75 g-OGTT at 30 min after load, IRI reached 6623 microU/ml, while plasma glucose level was 88 mg/dl. The anti-insulin antibody was not present. Since attempts at tumor localization by imaging techniques failed and the patient refused further examinations or surgical treatment, we recommended her to take a medication with a somatostatin analogue. Insulin suppression test using 50 microg of octreotide improved plasma glucose and IRI levels, suggesting the usefulness of the treatment, and a monthly administration of 20 mg of long-acting octreotide has successfully controlled her symptoms of hypoglycemia for 10 months. Our case demonstrated the utility of the long-acting somatostatin analogue for long-term treatment of undetermined hyperinsulinemia. A preliminary loading test using short-acting octreotide may be useful to determine appropriate medication, especially in cases who cannot receive surgical treatment.     

Case Report: Adult Nesidioblastosis A Case Report and Review of the Literature

George F. Laidlaw first described a pancreatic abnormality now known to be the most common cause of persistent hyperinsulinemic hypoglycemia in infants in 1938 (1, 2). The term he coined, nesidioblastosis, is derived from the Greek words for islets (nesidia) and germ (blastos) (3). It accurately describes the characteristic feature of nesidioblastosis, islet cells differentiating and budding from ductal epithelium. In adults, hyperinsulinemic hypoglycemia is rarely caused by nesidioblastosis and is usually caused by insulinoma or exogenous insulin treatment (4, 5). The first case series of adult nesidioblastosis was reported by Harness et al in 1981 (6). Since this case series of six patients, there have been only sporadic literature reports of adult nesidioblastosis, documenting fewer than 20 cases of adult nesidioblastosis over the past 15 years (3, 7-10). This paper presents an adult patient with hyperinsulinemic hypoglycemia due to nesidioblastosis and provides a guide to the diagnosis and treatment of this rare disorder in the adult population.     

Clinical case seminar: hypoglycemia after pancreas transplantation: association with allograft nesidiodysplasia and expression of islet neogenesis-associated peptide

We report a case of severe hypoglycemia occurring in a 35-yr-old woman, 6 yr after pancreas transplantation for type 1 diabetes mellitus. Extensive preoperative and intraoperative exploration failed to disclose the presence of a focal adenomatous lesion. Partial allograft pancreatectomy was performed initially, but it failed to control the hypoglycemic symptoms, leading to complete removal of the pancreas allograft. Histopathological examination of the resected pancreas allograft showed the presence of nesidioblastosis, characterized by foci of islet cells budding off ducts, accompanied by an increase in the number of islets, numerous small intralobular islet cell aggregates, and nesidiodysplasia (large, hyperchromatic islet cell nuclei). Islet neogenesis-associated protein-positive islets and ducts were seen by immunofluorescence. Insulin-positive islets ranged from very small to large, with isolated insulin-positive cells diffusely scattered, consistent with islet neogenesis. Very little glucagon staining was identified. Reported cases of adult nesidioblastosis are reviewed. The significance of nesidioblastosis in the context of pancreas transplantation and possible mechanisms of posttransplant hypoglycemia are discussed.     

Hypoglycémie et insulinome

Insulinomas are rare causes of hypoglycemia. After having ruled out non insulinomatous causes of hypoglycemia in a patient in whom Whipple's triad is documented, hyperinsulinism must be demonstrated biochemically, either during a spontaneous hypoglycemic episode or, more often, during a supervised fast which may be prolonged up to 72h. A mixed-meal test may also help to diagnose the very rare cases of postprandial hypoglycemia related to non insulinoma pancreatogenic hypoglycemic syndrome (NIPHS) or to some rare insulinomas.Only when diagnosis of hypoglycemic hyperinsulinism is made, the tumor localization process may be initiated. This may be difficult due to the small size of insulinomas (generally < 1 cm). Multimodal approach is necessary. The association of endoscopic ultrasound and CT-scan or MRI seems optimal. Octreoscan® will be also performed. First results with a very new technique, the GLP-1 receptor imaging, are promising for localizing very small tumors.This localization aims to allow a sparing surgery; enucleation of benign tumors, if possible, allows a pancreatic tissue preservation in patients with quite normal survival.     

Insulinoma accompanied by diabetes mellitus

A 53-year-old type 2 diabetic man was admitted due to spontaneous relatively hyperinsulinemic hypoglycemia. Oral glucose ingestion and arginine tolerance test showed hyperinsulinemic response. Arterial stimulation and venous sampling (ASVS) showed hyperinsulinemic response measured from the splenic artery after calcium gluconate stimulation. Diagnosis was insulinoma in the pancreas feeding from the artery. He has not suffered from spontaneous hypoglycemia since removal of the pancreatic body, tail and spleen. The specimen showed a solitary islet cell tumor. The high homeostasis model assessment of insulin resistance (HOMA-R) levels reflecting insulin resistance and hyperinsulinemic response after operation remained almost unchanged, indicating high insulin resistance and an insulin hypersecreting diabetic patient.     

High-dose calcium stimulation test in a case of insulinoma masquerading as hysteria

It is reported that some cases with insulinoma present with neuropsychiatric symptoms and are often misdiagnosed as psychosis. Here we report a case of insulinoma masquerading as hysteria, whose final diagnosis could be made using high-dose calcium stimulation test. A 28-yr-old woman was referred presenting with substupor, mutism, mannerism, restlessness, and incoherence. Laboratory examinations revealed hypoglycemia (33 mg/dL) and detectable insulin levels (9.7 μU/mL), suggesting the diagnosis of insulinoma. However, neither imaging studies nor selective arterial calcium injection (SACI) test with a conventional dose of calcium (0.025 mEq/kg) indicated the tumor. High-dose calcium injection (0.05 mEq/kg) evoked insulin secretion when injected into superior mesenteric artery. A solitary tumor in the head of the pancreas was resected, and her plasma glucose returned to normal. Postoperatively, iv injection of secretin resulted in a normal response of insulin, which was not found preoperatively. This case suggests the usefulness of the SACI test with high-dose of calcium in the case of insulinoma when the standard dose fails to detect such a tumor.     

A case of secretin-responsive insulinoma with low serum C-peptide levels

Insulinoma is the most common cause of fasting hypoglycemia resulting from autonomous insulin hypersecretion. A 59-year-old woman who had previously had an insulinoma and had undergone a partial pancreatectomy was admitted to our hospital because of recurrence of hypoglycemia after 27 years. She had two unusual endocrinological features: 1) the serum insulin response to intravenous secretin injection was not impaired, and 2) the serum C-peptide levels and ratios of serum C-peptide to insulin were relatively low. Two pancreatic tumors were readily detectable by computed tomography (CT) and magnetic resonance imaging (MRI). The selective arterial calcium injection (SACI) test showed a hyperinsulinemic response by calcium administration to the gastroduodenal artery. A partial pancreatectomy was done and her hypoglycemia disappeared. Histology revealed that the tumors were composed of monotonous, small round cells that were positive for both insulin and cathepsin B. As previous in vitro studies have shown that C-peptide can be metabolized within human insulinoma cells by proteolytic cleavage by cathepsin B, our patient's low serum C-peptide levels might have been caused by degradation of C-peptide by cathepsin B. According to the data from the literature, the molar ratio of serum C-peptide to insulin is generally decreased in patients with insulinoma than normal subjects. This case highlights the need for careful interpretation of C-peptide levels and the intravenous secretin injection test in the diagnosis of insulinoma.     

Clinical features and morphological characterization of 10 patients with noninsulinoma pancreatogenous hypoglycaemia syndrome (NIPHS)

OBJECTIVE: Noninsulinoma pancreatogenous hypoglycaemia syndrome (NIPHS), characterized by postprandial neuroglycopaenia, negative prolonged fasts and negative perioperative localization studies for insulinoma, but positive selective arterial calcium stimulation tests and nesidioblastosis in the gradient-guided resected pancreas, is a rare hypoglycaemic disorder of undetermined aetiology. We analysed the clinical, morphological and immunohistological features to further clarify the aetiology and pathogenesis of this rare disease. PATIENTS: Ten consecutive patients with NIPHS (nine men and one woman, aged 29-78 years) were included in the study. Six of the 10 received a gradient-guided subtotal (70%) or distal (50%) pancreatectomy. In the remaining four patients, diazoxide treatment was initiated and the precise mechanism of its action was assessed by meal tests. RESULTS: All of the patients showed a combination of postprandial neuroglycopaenia, negative prolonged fasts (except one patient) and negative localization studies for insulinoma, but positive calcium stimulation tests and nesidioblastosis in the gradient-guided resected pancreas. Immunohistological studies of the resected pancreatic tissues revealed neither an increased rate of proliferation of beta-cells nor an abnormal synthesis and/or processing of either proinsulin or amylin. Evidence of overexpression of the two pancreatic differentiation factors, PDX-1 and Nkx-6.1, as well as the calcium sensing receptor (CaSR) was absent. Nevertheless, abnormal expression of islet neogenesis-associated protein (INGAP), a human cytokine expressed only in the presence of islet neogenesis, in ducts and/or islets, was identified in three of the five patients studied. All of the six patients who received a surgical operation were relieved of further neuroglycopaenic attacks, but one patient who received a subtotal pancreatectomy developed diabetes. In the remaining four patients who received diazoxide treatment, hypoglycaemic episodes were satisfactorily controlled with an attenuated response of beta-cell peptides to meal stimulation. CONCLUSIONS: Our results strengthen the existence of this unique clinical hypoglycaemic syndrome from beta-cell hyperfunction as well as the value of the selective arterial calcium stimulation test in its correct diagnosis and localization. The mechanisms underlying beta-cell hyperfunction and release of insulin to calcium, however, remain poorly characterized. Nevertheless, in a subset of patients with NIPHS, there exists some, as yet undefined, pancreatic humoral/paracrine factor(s) other than proinsulin, amylin, PDX-1, Nkx-6.1 and possibly glucagon-like peptide-1 (GLP-1) that are capable of inducing the INGAP gene and, if activated, will initiate ductal proliferation and islet neogenesis. As for the treatment, we recommend that diazoxide be tried first in each patient and, should it fail, a gradient-guided subtotal or distal pancreatectomy be attempted.     

Glucose-responsive and octreotide-sensitive insulinoma

Insulinoma is the most common cause of fasting hypoglycemia resulting from autonomous insulin hypersecretion. We describe herein a unique case with paradoxical hypoglycemic episodes induced by hyperglycemia. A 55-year-old female had repeated hypoglycemic episodes after meal or during increased physical activity. Although fasting (10 hr) failed to provoke hypoglycemia, oral glucose tolerance test (GTT) caused an exaggerated insulin response (885 microU/ml) at 30 min, followed by hypoglycemia (36 mg/dl) after 90 min. Moreover, intravenous GTT also induced an exaggerated insulin response (>2900 microU/ml) at 10 min, followed by hypoglycemia (34 mg/dl) after 40 min. Although MRI and CT scan of the abdomen failed to detect any mass lesions in the pancreas, Octreoscan revealed increased radioactive uptake around the pancreatic head region. Treatment with a daily injection of octreotide (100 microg) alleviated her hypoglycemic episodes. At surgery, two islet cell adenomas were identified in the pancreas and resected. Postoperatively, she was free from hypoglycemic episodes after meal. Postoperative oral and intravenous GTT did not induce hypoglycemia. Thus, this is a very rare case of glucose-responsive and octreotide-sensitive insulinoma in whom GTT and octreotide proved to be a useful provocation and treatment for hypoglycemic episodes.     

Islet-cell hyperplasia causing hyperinsulinemic hypoglycemia in an adult

We report a patient, a 23-year-old man, who had clinical and laboratory findings suggestive of insulinoma. Although imaging studies did not reveal any tumors in the pancreas, distal pancreatectomy was performed because the possibility of small insulinoma could not be completely excluded. Grossly, the surgically removed pancreas did not reveal any tumors. Microscopically, the pancreas exhibited islet cell hyperplasia and nesidioblastosis. To our knowledge, this is the first authentic reported case of islet-cell hyperplasia occurring in a Japanese adult. Received Mar. 4, 1997; accepted May 23, 1997