[Recent progress in molecular biology of inherited tubular transport abnormalities].

Recent progress in the molecular biological approach to analysis of inherited tubular transport abnormalities is reviewed. 1) cDNAs of several mammalian proteins, related to amino acid transport in renal tubular cell, have been cloned using an expression cloning in Xenopus oocytes. One of them stimulates the transport of cystine, dibasic amino acids and neutral amino acids and will accelerate the analysis of cystinuria. 2) Isolation of cDNAs, encoding human and rat vasopressin V2 receptors, has been reported. The deduced amino acid sequence seems to be a member of receptors with seven putative transmembrane regions. Analysis of this gene from patients with nephrogenic diabetes insipidus is in progress. 3) Analysis of carbonic anhydrase II (CA II) gene in a Belgian family with renal tubular acidosis associated with osteoporosis and cerebral calcification has shown a point mutation replacing an invariant histidine residue of CA II protein with tyrosine. 4) Oculocerebrorenal syndrome of Lowe (OCRL) is a X-linked disorder affecting the lens, brain and kidneys. The OCRL locus has been mapped to Xq24-26 by linkage analysis and by finding de novo X-autosome translocations at Xq24-26 in two unrelated females with OCRL. A cDNA has been isolated using yeast artificial chromosome and DNA inserts that span the X chromosome breakpoint from a female patient. Transcript for this cDNA is absent in unrelated male patients. The open reading frame encodes a new protein similar to human inositol-polyphosphate-5-phosphatase, raising a possibility that OCRL is an inborn error of inositol phosphate metabolism.