Intestinal lipid malabsorption, resulting from an impaired formation or secretion of chylomicrons and associated with severe hypobetalipoproteinemia (HBL), may be due to biallelic mutations in APOB (homozygous FHBL type-1), MTTP (abetalipoproteinemia), or SAR1B (chylomicron retention disease).
Abetalipoproteinemia (ABL) is a rare recessive monogenic disease due to MTTP (microsomal triglyceride transfer protein) mutations leading to the absence of plasma apoB-containing lipoproteins.
Nevertheless, we found increased abundance of fecal Akkermansia from two adult ABL subjects with MTTP mutations compared to their heterozygous parents and within the range noted in six healthy control subjects.
Abetalipoproteinemia and homozygous hypobetalipoproteinemia are classical Mendelian autosomal recessive and co-dominant conditions, respectively, which are phenotypically similar and are usually caused by bi-allelic mutations in MTTP and APOB genes, respectively.
Using induced pluripotent stem cells (iPSCs) generated from an ABL patient homozygous for a missense mutation (MTTP<sup>R46G</sup>), we show that human hepatocytes and cardiomyocytes exhibit defects associated with ABL disease, including loss of apolipoprotein B (apoB) secretion and intracellular accumulation of lipids.
ABL (ABL1) and ARG (ABL2) are highly homologous to each other in overall domain structure and amino-acid sequence, with the exception of their C termini.
Structure-function analyses of microsomal triglyceride transfer protein missense mutations in abetalipoproteinemia and hypobetalipoproteinemia subjects.
Characterization of mutations in MTP causing abetalipoproteinemia has revealed that the central α-helical and C-terminal β-sheet domains are important for protein disulfide isomerase binding and lipid transfer activity.
Characterization of mutations in MTP causing abetalipoproteinemia has revealed that the central α-helical and C-terminal β-sheet domains are important for protein disulfide isomerase binding and lipid transfer activity.
Our results demonstrated that ABL SH3 mutant T79Y markedly repressed the expression of BCR-ABL signaling pathways in IM-resistant cell lines KCL22 and K562/G01 as well as IM-sensitive cell line K562.
Several mutations in the apoB, proprotein convertase subtilisin/kexin type 9 (PCSK9), and MTP genes result in low or absent levels of apoB and LDL-cholesterol in plasma, which cause familial hypobetalipoproteinemia and abetalipoproteinemia.
Sanger sequencing of MTTP was performed for two unrelated consanguineous Tunisian families with two affected individuals each, presenting a more severe ABL phenotype than previously reported in the literature.
These studies indicate that missense mutations Y528H, R540C, and N649S appear to cause ABL by reducing MTTP activity rather than by reducing binding of MTTP with protein disulfide isomerase or apoB.