Mitchell-Riley Syndrome: Improving Clinical Outcomes and Searching for Functional Impact of RFX-6 Mutations

AIMS/HYPOTHESIS

Caused by biallelic mutations of the gene encoding the transcription factor RFX6, the rare Mitchell-Riley syndrome (MRS) comprises neonatal diabetes, pancreatic hypoplasia, gallbladder agenesis or hypoplasia, duodenal atresia, and severe chronic diarrhea. So far, sixteen cases have been reported, all with a poor prognosis. This study discusses the multidisciplinary intensive clinical management of 4 new cases of MRS that survived over the first 2 years of life. Moreover, it demonstrates how the mutations impair the RFX6 function.

METHODS

Clinical records were analyzed and described in detail. The functional impact of two RFX6^R181W and RFX6^V506G variants was assessed by measuring their ability to transactivate insulin transcription and genes that encode the L-type calcium channels required for normal pancreatic beta-cell function.

RESULTS

All four patients were small for gestational age (SGA) and prenatally diagnosed with duodenal atresia. They presented with neonatal diabetes early in life and were treated with intravenous insulin therapy before switching to subcutaneous insulin pump therapy. All patients faced recurrent hypoglycemic episodes, exacerbated when parenteral nutrition (PN) was disconnected. A sensor-augmented insulin pump therapy with a predictive low-glucose suspension system was installed with good results. One patient had a homozygous c.1517T>G (p.Val506Gly) mutation, two patients had a homozygous p.Arg181Trp mutation, and one patient presented with new compound heterozygosity. The RFX6^V506G and RFX6^R181W mutations failed to transactivate the expression of insulin and genes that encode L-type calcium channel subunits required for normal pancreatic beta-cell function.

CONCLUSIONS/INTERPRETATION

Multidisciplinary and intensive disease management improved the clinical outcomes in four patients with MRS, including adjustment of parenteral/oral nutrition progression and advanced diabetes technologies. A better understanding of RFX6 function, in both intestine and pancreas cells, may break ground in new therapies, particularly regarding the use of drugs that modulate the enteroendocrine system.

Dietary Patterns, Ultra-processed Food, and the Risk of Inflammatory Bowel Diseases in the NutriNet-Santé Cohort

BACKGROUND

The incidence of inflammatory bowel diseases (IBDs) tended to increase for several decades. Diet is suspected to be a major determinant of the occurrence of these diseases. This prospective study aimed to assess the associations among occurrence of IBD, dietary patterns, and ultra-processed food in the French NutriNet-Santé cohort.

METHODS

Participants of the NutriNet-Santé cohort who completed at least three 24-hour dietary records were included. Incident IBD cases were identified from 3 questionnaires and confirmed by phone or email interview. Major dietary patterns (DPs) were computed using a principal component analysis (PCA) based on 29 food groups' consumption, whereas proportions of ultra-processed foods (UPFs) were obtained using the NOVA classification. Multivariable Poisson models were performed to evaluate associations among DP quintiles, UPF proportion (UPFp) in the diet, and incident IBD.

RESULTS

A total of 105,832 participants were included, contributing 238,924 person-years in a mean follow-up of 2.3 ± 2.2 years. Among them, 75 participants reported an incident IBD. Three major DPs were retained: "healthy," "traditional," and "western." No significant association was found for DPs and UPFp after adjustments for covariates.

CONCLUSIONS

In this study, neither DPs nor UPF proportion in the diet were significantly associated with the risk of incident IBD after adjustments for covariates. Further studies are needed to investigate the long-term association between diet and IBD.

Guidelines for the management of children at risk of secondary bone fragility: Expert opinion of a French working group

The current French national guidelines were elaborated by a working group consisting of experts in the field of pediatric endocrinology, rheumatology, hepatogastroenterology, nephrology, and pneumology. A systematic search was undertaken of the literature published between 2008 and 2018 and indexed in PubMed. The recommendations developed were then validated by an external evaluation group comprising representatives from the various highly specialized fields in pediatrics, representatives of the societies and groups supporting the development of the guidelines, and representatives of different healthcare professions. The objective of these guidelines was to detail the current optimal management of children at risk of secondary bone fragility.

Combined Immunodeficiency in Patients With Trichohepatoenteric Syndrome

The syndromic diarrhea/trichohepatoenteric syndrome (SD/THE) is a rare and multi-system genetic disorder caused by mutation in SKIV2L or in TTC37, two genes encoding subunits of the putative human SKI complex involved in RNA degradation. The main features are intractable diarrhea of infancy, hair abnormalities, facial dysmorphism, and intrauterine growth restriction. Immunologically this syndrome is associated with a hypogammaglobulinemia leading to an immunoglobulin supplementation. Our immune evaluation of a large French cohort of SD/THE patient revealed several immunological defects. First, switched memory B lymphocytes count is very low. Second, IFN-γ production by T and NK cells is impaired and associated with a reduced degranulation of NK cells. Third, T cell proliferation was abnormal in 3/6 TTC37-mutated patients. These three patients present with severe EBV infection and a transient hemophagocytosis which may be related to these immunological defects. Moreover, an immunological screening of patients with clinical features of SD/THE could facilitate both diagnosis and therapeutic management of these patients.