👤 Hiroshi Kitabayashi

Cerebrotendinous xanthomatosis is a rare autosomal recessive lipid storage disorder involving bile acid biosynthesis. Reduced mitochondrial cytochrome P450 enzyme activity leads to abnormal lipid accumulation in various tissues, especially tendons, lenses, and the central and peripheral nervous systems. This condition manifests with systemic symptoms such as neurological disorders, atherosclerosis, tendon xanthomas, and cataracts. Cerebrotendinous xanthomatosis typically presents in individuals with homozygous or compound heterozygous mutations in the CYP27A1 gene because of its autosomal recessive inheritance pattern. However, the phenotypic expression in heterozygous carriers remains uncertain. We report a 53-year-old Japanese man who was clinically diagnosed with familial hypercholesterolemia. He presented with marked Achilles tendon xanthomas and refractory hyper-low-density-lipoprotein cholesterolemia. Initiation of intensified lipid-lowering therapy, including inclisiran, resulted in improvement of hyper-low-density-lipoprotein cholesterolemia. Genetic testing revealed heterozygous mutations in CYP27A1 (p.Arg405Gln) and apolipoprotein B (APOB) (p.Pro955Ser). He had no neurological symptoms, cataracts, or other features suggestive of cerebrotendinous xanthomatosis without Achilles tendon xanthomas. This case highlights a rare presentation of a potential CYP27A1 heterozygous mutation-related phenotype. The APOB (p.Pro955Ser) variant is associated with reduced low-density-lipoprotein receptor activity, contributing to hyper-low-density-lipoprotein cholesterolemia and Achilles tendon xanthomas. However, this patient's Achilles tendon xanthoma was thicker than those reported in previous cases with APOB (p.Pro955Ser) gene mutations, suggesting a potential contribution from the CYP27A1 mutation. Although the patient did not exhibit elevated serum cholestanol levels or other cerebrotendinous xanthomatosis features, the marked Achilles tendon thickening raises the possibility that the combination of a heterozygous CYP27A1 gene mutation and an APOB gene mutation contributed to the condition. Show less

Epigenetic regulation is required to ensure the precise spatial and temporal pattern of gene expression that is necessary for embryonic development. Although the roles of some epigenetic modifications in embryonic development have been investigated in depth, the role of methylation at lysine 79 (H3K79me) is poorly understood. Dot1L, a unique methyltransferase for H3K79, forms complexes with distinct sets of co-factors. To further understand the role of H3K79me in embryogenesis, we generated a mouse knockout of Mllt10, the gene encoding Af10, one Dot1L complex co-factor. We find homozygous Mllt10 knockout mutants (Mllt10-KO) exhibit midline facial cleft. The midfacial defects of Mllt10-KO embryos correspond to hyperterolism and are associated with reduced proliferation of mesenchyme in developing nasal processes and adjacent tissue. We demonstrate that H3K79me level is significantly decreased in nasal processes of Mllt10-KO embryos. Importantly, we find that expression of AP2α, a gene critical for midfacial development, is directly regulated by Af10-dependent H3K79me, and expression AP2α is reduced specifically in nasal processes of Mllt10-KO embryos. Suppression of H3K79me completely mimicked the Mllt10-KO phenotype. Together these data are the first to demonstrate that Af10-dependent H3K79me is essential for development of nasal processes and adjacent tissues, and consequent midfacial formation. Show less

The CALM-AF10 fusion gene, which results from a t(10;11) translocation, is found in a variety of hematopoietic malignancies. Certain HOXA cluster genes and MEIS1 genes are upregulated in patients and mouse models that express CALM-AF10. Wild-type clathrin assembly lymphoid myeloid leukemia protein (CALM) primarily localizes in a diffuse pattern within the cytoplasm, whereas AF10 localizes in the nucleus; however, it is not clear where CALM-AF10 acts to induce leukemia. To investigate the influence of localization on leukemogenesis involving CALM-AF10, we determined the nuclear export signal (NES) within CALM that is necessary and sufficient for cytoplasmic localization of CALM-AF10. Mutations in the NES eliminated the capacity of CALM-AF10 to immortalize murine bone-marrow cells in vitro and to promote development of acute myeloid leukemia in mouse models. Furthermore, a fusion of AF10 with the minimal NES can immortalize bone-marrow cells and induce leukemia in mice. These results suggest that during leukemogenesis, CALM-AF10 plays its critical roles in the cytoplasm. Show less