Identification of novel OCRL isoforms associated with phenotypic differences between Dent disease-2 and Lowe syndrome.

BACKGROUND: Although Lowe syndrome and Dent disease-2 are caused by Oculocerebrorenal syndrome of Lowe (OCRL) mutations, their clinical severities differ substantially and their molecular mechanisms remain unclear. Truncating mutations in OCRL exons 1-7 lead to Dent disease-2, whereas those in exons 8-24 lead to Lowe syndrome. Herein we identified the mechanism underlying the action of novel OCRL protein isoforms. METHODS: Messenger RNA samples extracted from cultured urine-derived cells from a healthy control and a Dent disease-2 patient were examined to detect the 5' end of the OCRL isoform. For protein expression and functional analysis, vectors containing the full-length OCRL transcripts, the isoform transcripts and transcripts with truncating mutations detected in Lowe syndrome and Dent disease-2 patients were transfected into HeLa cells. RESULTS: We successfully cloned the novel isoform transcripts from OCRL exons 6-24, including the translation-initiation codons present in exon 8. In vitro protein-expression analysis detected proteins of two different sizes (105 and 80 kDa) translated from full-length OCRL, whereas only one protein (80 kDa) was found from the isoform and Dent disease-2 variants. No protein expression was observed for the Lowe syndrome variants. The isoform enzyme activity was equivalent to that of full-length OCRL; the Dent disease-2 variants retained >50% enzyme activity, whereas the Lowe syndrome variants retained <20% activity. CONCLUSIONS: We elucidated the molecular mechanism underlying the two different phenotypes in OCRL-related diseases; the functional OCRL isoform translated starting at exon 8 was associated with this mechanism.

Association between Crohn's disease and AarF domain-containing kinase 4 glomerulopathy.

Coenzyme Q10 deficiency causing gastrointestinal symptoms has not been reported. At least 15 genes are involved in CoQ10 biosynthesis, and one of the genes is AarF domain-containing kinase 4 (ADCK4). This case report first showed a patient who presented with Crohn's disease (CD) combined with ADCK4 glomerulopathy (ADCK4-GN). After approximately 2 years of infliximab treatment for CD, this patient has remained in clinical remission with no adverse effects. Moreover, two important findings were obtained: first, individuals with ADCK4-GN may present with complications, such as CD, which is a gastrointestinal disease, and infliximab may be effective for CD associated with ADCK4-GN. Second, infliximab may also be effective and safe for individuals with CD who are undergoing peritoneal dialysis. Thus, the results of the present study may be used in managing patients with such condition, and as a result, better clinical outcomes will be obtained.