Persistent Hyperinsulinemic Hypoglycemia with Pancreatic Teratoma in Infancy: A Case Report

Background

Persistent hyperinsulinemic hypoglycemia of infancy (PHHI) is a rare genetic disorder in newborns and infants. It is commonly due to mutations of genes that regulate insulin secretion from the beta cells of the pancreas, resulting in focal or diffuse pancreatic hyperplasia [1–5]. The incidence of PHHI is about 1 in 35 000 live births, but it is more prevalent in countries with a high consanguinity rate [1,2]. Severe cases usually present in the newborn period, whereas diagnosis of less severe forms may be delayed until 3 to 6 months of age. PHHI presents with an inappropriately high insulin level in the face of hypoglycemia and an absence of ketosis. Hyperinsulinism suppresses ketone production and gluconeogenesis, making infant brains even more vulnerable to hypoglycemic damage [1–4]. Prompt diagnosis and treatment is therefore crucial to prevent irreversible brain damage. We are presenting a case of severe hyperinsulinemic hypoglycemia with an abdominal mass in a 6-month-old infant.

Case Report

HISTOPATHOLOGICAL FINDINGS:

The entire solid mass consisted of fetal pancreatic tissue similar to that at 3 months’ gestation, based on embryologic staging of pancreatic ductal and acinar structures. Almost 95% of the mass consisted of islets of Langerhans. The immune-histo-chemical testing revealed an abundance of insulin-secreting beta cells with scattered areas of glucagon and few somatostatin-secreting cells, which are seen in the early embryologic stage of development (Figure 3).

GENETIC EVALUATION:

Her karyotype was 46 XX with no deletion, duplication, or aberrant methylation profile of one or more sequences of the KvDMR and H19DMR domains in the 11p15 BWS/Russell-Silver syndrome region. Chimerism testing of the surgically removed material and the blood sample of the infant was performed by using an AmpFlSTR Identifiler PCR Amplification kit (Applied Biosystems, Warrington, UK). Briefly, we used 17 different STR markers located at 2p23-2per, 2q35-37.1, 3p21.31, 4q28, 5q21-31, 5q33.3-34, 7q11.21-22, 8q24.3, 11p15.5, 12p12-pter, 13q22-31, 16q24-qter, 18q21.3, 19q12-13.1, 21q11.2-q21, Xp22.1-22.3, and Yp11.2. The analysis showed that the surgical material and the baby were genetically identical. The zygocity testing of the surgical material demonstrated homo-zygocity at the centromeric region. Whole exon sequencing (WES) of the infant’s peripheral blood showed negative mutation of the ABCC8 gene and heterozygous variation of hepatocyte nuclear factor-1 beta (HNF1β), (exon 1 (rs747555052), c.79G>C, p.V27L) and insulin receptor substrate 1 (IRS1) (exon 1 (rs779584301), c.1860 C>T, p.P454S) genes.

Postoperatively she had marked hyperglycemia, but after 24 h her blood glucose normalized with complete resolution of her hyperinsulinemic hypoglycemia. At age 8.5 months she was diagnosed with a congenital hiatal hernia and underwent corrective surgery at 11 months. Histologic examination of the surgical material showed mature squamous epithelium and was thought to be residue of the previously removed mature teratoma. The patient is currently 2.5 years of age and has had no subsequent episodes of clinical or biochemical hypoglycemia.

Discussion

The mechanism of action was initially unclear in this case of hyperinsulinemic hypoglycemia with teratoma in this 6-month-old infant. Insulinoma is a very rare cause of hyperinsulinemic hypoglycemia in childhood [6] and therefore had not been considered due to her age and the presence of an intra-abdominal mass without connection to her normal appearing pancreas. The solid component of the mass connected to the wall of the cyst by a 2.5-cm stalk raised the suspicion of a case of fetus in fetu (FIF). The differential diagnoses included pancreatic heterotopias, mature cystic teratoma (MCT), and FIF. Pancreatic heterotopia is a rare congenital anomaly in which there is pancreatic tissue with no anatomic connection to the pancreas itself [7]. Pancreatic heterotopia is commonly an incidental finding in adults and very rarely reported to cause hyperinsulinemic hypoglycemia [8]. In MCT the presence of various tissue types in a cystic mass is characteristic. The presence of mature pancreatic tissue in mediastinal teratomas has been reported; however, none of the cases resulted in hyper-insulinemic hypoglycemia [8–11]. Although diagnostic criteria have been proposed for FIF [12], the differentiation between MCT and FIF is still controversial [13–16]. All cases of FIF occur in identical twins and are always genetically identical to the host. It has been reported that MCT and FIF could be differentiated by zygosity [16]. Teratomas are always homozygous at or near the centromeric regions [17]. Although this mass fulfilled the diagnostic criteria of FIF [12], it was homozygous at the centromeric region, confirming the diagnosis of an MCT. The presence of a squamous epithelium in a small region was also consistent with a teratoid maturation.

The most interesting point of this case is that the mature teratoma with immature fetal pancreatic tissue lacked the normal control mechanisms of insulin secretion. Having extra beta cells does not cause hyperinsulinemic hypoglycemia if the beta cell function is properly regulated. During the first trimester, beta cells have immature glucose sensing mechanisms [18]. The insulin secretion from the fetal pancreas during early stages of maturation responds to amino acid rather than to glucose concentrations, and at 12 to 22 weeks’ gestation, basal insulin secretion from the fetal pancreas is 4-fold higher [19]. Therefore, immaturity of the fetal pancreatic tissue may be the reason for the uncontrolled insulin secretion and partial response to diazoxide treatment. Unfortunately, WES on the tumor tissue could not be performed due to the quality and quantity of the available DNA, and we cannot totally exclude the possibility of a mutation in the teratoma that could have caused uncontrolled insulin secretion. The WES of the peripheral blood, however, detected a heterozygous variation of HNF1β and IRS1 genes but no mutation of the ABCC8 gene. The heterozygous IRS1 variation detected in this case is known to be associated with type 2 diabetes and susceptibility to insulin resistance [20] and therefore could be a coincidental finding. However, the combination of heterozygous variations of the HNF1β and IRS1 genes may be a new finding for the pathogenesis of persistent hyperinsulinemic hypoglycemia in infants. HNF1β plays an important role in organogenesis, especially of the liver, kidney, and pancreas. Mutations in the HNF1β gene cause monogenic diabetes in youth type 5 (MODY5), renal cysts, genital malformations, and pancreas atrophy [21]. Mutations in the HNF1β gene have not been reported to cause hyperinsulinemic hypoglycemia. This infant had a right ureteropelvic junction stenosis and grade III hydronephrosis which could have been due to the detected variation of the HNF1β gene. About one-third of patients with an HNF1β mutation have pancreatic structural anomalies, but a pancreatic teratoma has never been reported with variations or mutations of the HNF1β gene [22]. The specific variation in the HNF1β gene detected in this infant has been reported previously and is considered to be a benign variant or variation of unknown significance [23,24]. This variation was located at the dimerization domain of the HNF1β protein, which is important for protein function and therefore might have impacted the embryogenesis of the pancreas, causing a pancreatic teratoma with uncontrolled insulin secretion and severe hyperinsulinemic hypoglycemia in this infant.

Conclusions

The combination of heterozygous variations of HNF1β and IRS1 genes in this infant likely played a role in the embryogenesis in utero, causing a pancreatic teratoma and severe hyperinsulinemic hypoglycemia. Therefore, this should be considered in the pathogenesis of persistent hyperinsulinemic hypoglycemia in infants.