Keith J. Lindley

A recessive contiguous gene deletion causing infantile hyperinsulinism, enteropathy and deafness identifies the Usher type 1C gene

Usher syndrome type 1 describes the association of profound, congenital sensorineural deafness, vestibular hypofunction and childhood onset retinitis pigmentosa. It is an autosomal recessive condition and is subdivided on the basis of linkage analysis into types 1A through 1E (refs 2–6). Usher type 1C maps to the region containing the genes ABCC8 and KCNJ11 (encoding components of ATP-sensitive K + (KATP) channels), which may be mutated in patients with hyperinsulinism. We identified three individuals from two consanguineous families with severe hyperinsulinism, profound congenital sensorineural deafness, enteropathy and renal tubular dysfunction. The molecular basis of the disorder is a homozygous 122-kb deletion of 11p14–15, which includes part of ABCC8 and overlaps with the locus for Usher syndrome type 1C and DFNB18 (ref. 11). The centromeric boundary of this deletion includes part of a gene shown to be mutated in families with type 1C Usher syndrome, and is hence assigned the name USH1C. The pattern of expression of the USH1C protein is consistent with the clinical features exhibited by individuals with the contiguous gene deletion and with isolated Usher type 1C.

Small-intestinal dysfunction accompanies the complex endocrinopathy of human proprotein convertase 1 deficiency

We have previously described the only reported case of human proprotein convertase 1 (PC1) deficiency, in a female (Subject A) with obesity, hypogonadism, hypoadrenalism, and reactive hypoglycemia. We now report the second case of human PC1 deficiency (Subject B), also due to compound heterozygosity for novel missense and nonsense mutations. While both subjects shared the phenotypes of obesity, hypoadrenalism, reactive hypoglycemia, and elevated circulating levels of certain prohormones, the clinical presentation of Subject B was dominated by severe refractory neonatal diarrhea, malabsorptive in type. Subsequent investigation of Subject A revealed marked small-intestinal absorptive dysfunction, which was not previously clinically suspected. We postulate that PC1, presumably in the enteroendocrine cells, is essential for the normal absorptive function of the human small intestine. The differences in the nature and severity of presentation between the two cases cannot readily be explained on the basis of allelic heterogeneity, as the nonsense and missense mutations from both subjects had comparably severe effects on the catalytic activity of PC1. Despite Subject As negligible PC1 activity, some mature ACTH and glucagon-like peptide 17-36(amide) were detectable in her plasma, suggesting that the production of these hormones, at least in humans, does not have an absolute dependence on PC1. The presence of severe obesity and the absence of growth retardation in both subjects contrast markedly with the phenotype of mice lacking PC1 and suggest that the precise physiological repertoire of this enzyme may vary between mammalian species.

A Mutation in the Thyroid Hormone Receptor Alpha Gene

Thyroid hormones exert their effects through alpha (TRα1) and beta (TRβ1 and TRβ2) receptors. Here we describe a child with classic features of hypothyroidism (growth retardation, developmental retardation, skeletal dysplasia, and severe constipation) but only borderline-abnormal thyroid hormone levels. Using whole-exome sequencing, we identified a de novo heterozygous nonsense mutation in a gene encoding thyroid hormone receptor alpha (THRA) and generating a mutant protein that inhibits wild-type receptor action in a dominant negative manner. Our observations are consistent with defective human TRα-mediated thyroid hormone resistance and substantiate the concept of hormone action through distinct receptor subtypes in different target tissues.

Inflammatory Skin and Bowel Disease Linked to ADAM17 Deletion

We performed genetic and immunohistochemical studies in a sister and brother with autosomal recessive neonatal inflammatory skin and bowel lesions. The girl died suddenly at 12 years of age from parvovirus B19-associated myocarditis; her brother had mild cardiomyopathy. We identified a loss-of-function mutation in ADAM17, which encodes a disintegrin and metalloproteinase 17 (also called tumor necrosis factor α [TNF-α]-converting enzyme, or TACE), as the probable cause of this syndrome. Peripheral-blood mononuclear cells (PBMCs) obtained from the brother at 17 years of age showed high levels of lipopolysaccharide-induced production of interleukin-1β and interleukin-6 but impaired release of TNF-α. Despite repeated skin infections, this young man has led a relatively normal life. (Funded by Barts and the London Charity and the European Commission Seventh Framework Programme.).

A major role for intestinal epithelial nucleotide oligomerization domain 1 (NOD1) in eliciting host bactericidal immune responses to Campylobacter jejuni

Campylobacter jejuni is the foremost cause of bacterial‐induced diarrhoeal disease worldwide. Although it is well established that C. jejuni infection of intestinal epithelia triggers host innate immune responses, the mechanism(s) involved remain poorly defined. Innate immunity can be initiated by families of structurally related pattern‐recognition receptors (PRRs) that recognize specific microbial signature motifs. Here, we demonstrated maximal induction of epithelial innate responses during infection with live C. jejuni cells. In contrast when intestinal epithelial cells (IECs) were exposed to paraformaldehyde‐fixed bacteria, host responses were minimal and a marked reduction in the number of intracellular bacteria was noted in parallel. These findings suggested a role for intracellular host–C. jejuni interactions in eliciting early innate immunity. We therefore investigated the potential involvement of a family of intracellular, cytoplasmic PRRs, the nucleotide‐binding oligomerization domain (NOD) proteins in C. jejuni recognition. We identified NOD1, but not NOD2, as a major PRR for C. jejuni in IEC. We also found that targeting intestinal epithelial NOD1 with small interfering RNA resulted in an increase in number of intracellular C. jejuni, thus highlighting a critical role for NOD1‐mediated antimicrobial defence mechanism(s) in combating this infection at the gastrointestinal mucosal surface.

Colitis in chronic granulomatous disease

BACKGROUND Involvement of the gut in chronic granulomatous disease (CGD) has been previously described and colitis highlighted. However, the nature and histopathology of the colitis are unclear and have been thought to be non-specific or similar to Crohns disease. METHODS Seven patients with CGD, suffering from gastrointestinal symptoms were prospectively studied. RESULTS All patients had anaemia; other symptoms were failure to thrive (5/7) and diarrhoea (5/7). Most had microcytic anaemia (5/7), increased platelets (7/7), and increased erythrocyte sedimentation rate (6/6). Endoscopically there was a friable erythematous mucosa in 6/7. The histological features present in all patients consisted of a colitis with paucity of neutrophils, increased numbers of eosinophils, eosinophilic crypt abscesses, pigmented macrophages, and nuclear debris. In some granulomas were present (2/7). CONCLUSIONS Colitis is a common cause of gastrointestinal symptoms in CGD and is caused by a non-infective inflammatory process. The histology has specific features, which are distinctive from those seen in Crohns disease.

Gastrointestinal complications of epidermolysis bullosa in children

Background  Epidermolysis bullosa (EB) is a group of inherited disorders characterized by skin and mucous membrane fragility. Gastrointestinal (GI) complications have been described in many types of EB and are responsible for significant morbidity.

Engineering a glucose-responsive human insulin-secreting cell line from islets of Langerhans isolated from a patient with persistent hyperinsulinemic hypoglycemia of infancy

Persistent hyperinsulinemic hypoglycemia of infancy (PHHI) is a neonatal disease characterized by dysregulation of insulin secretion accompanied by profound hypoglycemia. We have discovered that islet cells, isolated from the pancreas of a PHHI patient, proliferate in culture while maintaining a beta cell-like phenotype. The PHHI-derived cell line (NES2Y) exhibits insulin secretory characteristics typical of islet cells derived from these patients, i.e. they have no KATP channel activity and as a consequence secrete insulin at constitutively high levels in the absence of glucose. In addition, they exhibit impaired expression of the homeodomain transcription factor PDX1, which is a key component of the signaling pathway linking nutrient metabolism to the regulation of insulin gene expression. To repair these defects NES2Y cells were triple-transfected with cDNAs encoding the two components of the KATP channel (SUR1 and Kir6.2) and PDX1. One selected clonal cell line (NISK9) had normal KATPchannel activity, and as a result of changes in intracellular Ca2+ homeostasis ([Ca2+] i ) secreted insulin within the physiological range of glucose concentrations. This approach to engineering PHHI-derived islet cells may be of use in gene therapy for PHHI and in cell engineering techniques for administering insulin for the treatment of diabetes mellitus.

Therapy for persistent hyperinsulinemic hypoglycemia of infancy. Understanding the responsiveness of beta cells to diazoxide and somatostatin.

The neonatal disorder persistent hyperinsulinemic hypoglycemia of infancy (PHHI) arises as the result of mutations in the subunits that form the ATP-sensitive potassium (KATP) channel in pancreatic beta cells, leading to insulin hypersecretion. Diazoxide (a specific KATP channel agonist in normal beta cells) and somatostatin (octreotide) are the mainstay of medical treatment for the condition. To investigate the mechanism of action of these agents in PHHI beta cells that lack KATP currents, we applied patch clamp techniques to insulin-secreting cells isolated from seven patients with PHHI. Five patients showed favorable responses to medical therapy, and two were refractory. Our data reveal, in drug-responsive patients, that a novel ion channel is modulated by diazoxide and somatostatin, leading to termination of the spontaneous electrical events that underlie insulin hypersecretion. The drug-resistant patients, both of whom carried a mutation in one of the genes that encode KATP channel subunits, also lacked this novel K+ channel. There were no effects of diazoxide and somatostatin on beta cell function in vitro. These findings elucidate for the first time the mechanisms of action of diazoxide and somatostatin in infants with PHHI in whom KATP channels are absent, and provide a rationale for development of new therapeutic opportunities by K+ channel manipulation in PHHI treatment.

Persistent and chronic diarrhea and malabsorption: Working group report of the second world congress of pediatric gastroenterology, hepatology, and nutrition

ResearchAssessment of mucosal immunopathology and molecular and cellular biology of persistent diarrhea in representative populations in developing countries.Studies of small bowel microbiology in PD, especially in at-risk populations e.g., malnourished children and HIV endemic areas.Evaluation of the link of micronutrient deficiencies with PD and their relationship with intestinal repair mechanisms. InterventionImproved facility-based approaches and algorithms for the nutritional management of PD and malnutrition.Diagnosis and management of PD in public health system and primary care (including domiciliary) settings.Scaling-up environmental control measures and safe water and hygiene strategies. EducationContinuing medical education strategies to educate medical students and physicians in the recognition, management and prevention of PD.Education of nursing and paramedical personnel in the recognition and management of PD in ambulatory and health system settings.Community and public health education strategies for increased awareness of the prevention of PD and optimal management of acute and prolonged diarrheal episodes.