A rare cause of neonatal diarrhoea: Microvillositary inclusion disease: about a case report

Microvillositary inclusion disease also known as microvillositary atrophy is a rare congenital enteropathy containing a border abnormality in the brushes of enterocytes, manifesting as severe rebellious diarrhea in newborns and infants. It was first described in 1978 by Davidson, et al. The autosomal recessive mode of transmission is suggested because of the frequency of familial cases and inbreeding. Histopathology plays an essential role in establishing the diagnosis. In 2008, a common mutation was identified in most of the patients studied in the MYO5B gene that codes for the Myosin Vb protein, which helped in understanding the etiopathogeny of this pathology poorly described in the literature. The prognosis for this pathology is extremely bleak, requiring total parenteral nutrition for child survival. Intestinal transplantation is for the moment the only long-term solution. Materials and methods: We report the case of an infant aged 6 months, with no perinatal antecedent. There is 1st degree consanguinity, the mother has a history of deaths in younger siblings in undetermined circumstances. Who since the age of 3 days presents profuse liquid diarrhoea with malnutrition, dehydration and enormous abdominal distension? Several diagnoses were suspected before the jejune biopsy was carried out, which led to the diagnosis of a microvilliositary inclusion disease. The aim of our work is to highlight the rarest cause of neonatal rebel diarrhoea and to know how to include it among other differential diagnoses.

Control of Cytoskeletal Dynamics by β-Arrestin1/Myosin Vb Signaling Regulates Endosomal Sorting and Scavenging Activity of the Atypical Chemokine Receptor ACKR2

The atypical chemokine receptor ACKR2, formerly named D6, is a scavenger chemokine receptor with a non-redundant role in the control of inflammation and immunity. The scavenging activity of ACKR2 depends on its trafficking properties, which require actin cytoskeleton rearrangements downstream of a β-arrestin1-Rac1-PAK1-LIMK1-cofilin-dependent signaling pathway. We here demonstrate that in basal conditions, ACKR2 trafficking properties require intact actin and microtubules networks. The dynamic turnover of actin filaments is required to sustain ACKR2 constitutive endocytosis, while both actin and microtubule networks are involved in processes regulating ACKR2 constitutive sorting to rapid, Rab4-dependent and slow, Rab11-dependent recycling pathways, respectively. After chemokine engagement, ACKR2 requires myosin Vb activity to promote its trafficking from Rab11-positive recycling endosomes to the plasma membrane, which sustains its scavenging activity. Other than cofilin phosphorylation, induction of the β-arrestin1-dependent signaling pathway by ACKR2 agonists also leads to the rearrangement of microtubules, which is required to support the myosin Vb-dependent ACKR2 upregulation and its scavenging properties. Disruption of the actin-based cytoskeleton by the apoptosis-inducing agent staurosporine results in impaired ACKR2 internalization and chemokine degradation that is consistent with the emerging scavenging-independent activity of the receptor in apoptotic neutrophils instrumental for promoting efficient efferocytosis during the resolution of inflammation. In conclusion, we provide evidence that ACKR2 activates a β-arrestin1-dependent signaling pathway, triggering both the actin and the microtubule cytoskeletal networks, which control its trafficking and scavenger properties.

Microvillus Inclusion Disease: A Rare Mutation of STX3 in Exon 9 Causing Fatal Congenital Diarrheal Disease

Inherited diarrheal disorders cause serious morbidity resulting in dependence on intensive care and parenteral nutrition. Microvillus inclusion disease (MVID) has been classically described and results from mutations in the gene coding myosin Vb, which is responsible for enterocyte polarization. Newer reports of mutations resulting in truncated syntaxin 3 (STX3) and Munc18-2 (STXBP2) proteins have been elucidated as causative. To date, five cases of STX3 abnormalities resulting in MVID have been described. We report an infant who presented with congenital diarrhea and was determined to have a rare mutation of STX3. This new finding would be beneficial in future functional genotype–phenotype correlation studies.