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Objectives: Anorexia nervosa (AN) is an eating disorder accompanied by a low body mass index and (self-) restricted food intake. Nutritional limitations can cause complaints of the digestive system, because of a disturbed absorption of food components. The absorption of carbohydrates may be seriously affected and reduced to a minimum. On this basis, a possible connection between AN, and the prevalence of gastrointestinal symptoms due to malabsorption was examined. Methods: For the systematic literature research with the aim of a better understanding of the topic the databases PubMed, Web of Science, Cochrane Library, Livivo and Google Scholar were used. Results: After the manual selection process of 2215 retrieved studies, 89 full texts were read and according to the predetermined eligibility criteria, finally 2 studies on the monosaccharide fructose and disaccharide lactose were included in this review. Conclusion: Malabsorption is often observed in patients with AN. It may contribute to the gastrointestinal complaints reported by patients and hamper body weight regain. Among others, mucosal atrophy and duodenal transporter dysfunction are discussed as main reasons. In the future more studies on carbohydrate malabsorption related to low body weight as observed in AN are warranted and may be conducted rather in an outpatient setting. Plain English summary: People with anorexia nervosa (AN) may experience a preference for foods containing fewer calories but more carbohydrates, e.g. fruits and vegetables. The consequences of this food restriction and selection may include malabsorption of sugars such as fructose and lactose, the mechanism of which is incompletely understood. This may contribute to symptoms similar to those seen in people with lactose intolerance, e.g. bloating, and make it harder for people to eat recommended foods. This paper presents a comprehensive literature search for research on this topic. However, only two studies were identified which highlights that further investigation is needed to explore this clinically relevant field. [ABSTRACT FROM AUTHOR]

Background: Congenital lactase deficiency (CLD) is a rare severe autosomal recessive disorder, with symptoms like watery diarrhea, meteorism and malnutrition, which start a few days after birth by the onset of nursing. The most common rationales identified for this disorder are missense mutations or premature stop codons in the coding region of the lactase-phlorizin hydrolase (LPH) gene. Recently, two heterozygous mutations, c.4419C > G (p.Y1473X) in exon 10 and c.5387delA (p.D1796fs) in exon 16, have been identified within the coding region of LPH in a Japanese infant with CLD. Methods: Here, we investigate the influence of these mutations on the structure, biosynthesis and function of LPH. Therefore the mutant genes were transiently expressed in COS-1 cells. Results: We show that both mutant proteins are mannose-rich glycosylated proteins that are not capable of exiting the endoplasmic reticulum. These mutant proteins are misfolded and turnover studies show that they are ultimately degraded. The enzymatic activities of these mutant forms are not detectable, despite the presence of lactase and phlorizin active sites in the polypeptide backbone of LPH-D1796fs and LPH-Y1473X respectively. Interestingly, wild type LPH retains its complete enzymatic activity and intracellular transport competence in the presence of the pathogenic mutants suggesting that heterozygote carriers presumably do not show symptoms related to CLD. Conclusions: Our study strongly suggests that the onset of severe forms of CLD is elicited by mutations in the LPH gene that occur in either a compound heterozygous or homozygous pattern of inheritance. [ABSTRACT FROM AUTHOR]