Basic—Alimentary TractCompound Heterozygous Mutations Affect Protein Folding and Function in Patients With Congenital Sucrase-Isomaltase Deficiency
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Mutagenesis of a cDNA Encoding SI
The mutations identified previously18 were introduced by site-directed mutagenesis into the wild-type SI cloned in the vector pSG8-SI.7 The generated SI mutants are denoted hereafter as SI-V577G, SI-G1073D, SI-C1229Y, and SI-F1745C. The mutagenesis was performed by polymerase chain reaction using Isis-DNA Polymerase (MP Biomedicals, Eschwege, Germany) and the following oligonucleotides as primers: (1) SI-V577G: 5′-GAG CAA GCA GTA CAA AAA GGT TTT CCT AAT AAG AGA AGC-3′ (forward) and 5′-GCT TCT
General Description of Novel Mutations Associated With CSID
We recently identified the mutations V577G, G1073D, C1229Y, and F1745C in the SI protein by isolating and sequencing the genomic DNA of patients with symptoms typical of CSID.18 All the patients were of Hungarian origin. The mutations are compiled in Table 1, which also compares sequences in the immediate regions of affected residues and highlights the conserved nature of these residues among different species.
The mutation C1229Y is located in SUC and was found in 2 individuals who are full
Discussion
During the past decade several mutations have been characterized in the SI gene that are associated with the onset of disaccharide malabsorption in CSID. These mutations elicit alterations in the folding pattern, apical sorting fidelity, intracellular localization of SI, or function of SI. The diversity of these phenotypes has been instrumental in identifying sorting signals or proposing novel cell biological mechanisms such as secondary quality control. Until now each CSID phenotype has been
Acknowledgements
The authors thank Hans–Peter Hauri and Erwin Sterchi (Biozentrum Basel and University of Bern, respectively, both Switzerland) for the generous gifts of monoclonal anti–sucrase-isomaltase antibodies. The authors thank Dr Irma Korponay–Szabo, Children's Hospital, Budapest, Hungary, and Dr Petra Sander, University of Veterinary Medicine, Hannover, Germany, for participation in the initial phases of this project.
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M.A. and M.K. contributed equally to this work.
Conflict of interest The authors disclose no conflicts.
Funding Dr Naim was supported by the German Research Foundation (SFB 621, C8 project).