Two Novel Mutations in the Vasopressin V2 Receptor Gene in Unrelated Japanese Kindreds with Nephrogenic Diabetes Insipidus
| Title: | Two Novel Mutations in the Vasopressin V2 Receptor Gene in Unrelated Japanese Kindreds with Nephrogenic Diabetes Insipidus |
|---|---|
| Authors: | Tsukaguchi, Hiroyasu; Matsubara, Hiroaki; Aritaki, Sekoiya; Kimura, Tokihisa; Abe, Shuichi; Inada, Mitsuo |
| Publisher: | Biochemical and Biophysical Research Communications |
| Date Published: | December 15, 1993 |
| Reference Number: | 118 |
Nephrogenic diabetes insipidus (NDI) is a rare X-linked disorder exhibiting renal resistance to the antidiuretic action of arginine vasopressin (AVP). Recent elucidation of the vasopressin V2 (renal type) receptor gene structure has enabled us to test the hypothesis that the genetic defect in the V2 receptor is the likely molecular basis of NDI. By using the polymerase chain reaction (PCR)-direct sequencing, we identified novel V2 receptor gene mutations in two unrelated Japanese kindreds with NDI. In the male patients of kindred A, a single codon deletion in one of two consecutive GTC triplets (nucleotide 832 to 837) was detected. This base change resulted in the loss of a valine residue in the 6th transmembrane domain. In the affected males of kindred B, a G to C substitution was found at nucleotide 428, altering codon 143 from arginine (CGT) to proline (CCT) in the second cytoplasmic domain. PCR-single strand conformation polymorphism (SSCP) analysis of family members demonstrated that the mutations cosegregated with clinically affected individuals and were absent in normal subjects. Our results suggest that different V2 receptor defects could be responsible for AVP resistance in individual NDI kindreds.
You may, however, obtain this article at the pub To return to this page, use your "back" key. |
This translation by the NDI Foundation is to assist the lay reader. To provide a clear, accessible interpretation of the original article, we eliminated or simplified some technical detail and complicated scientific language. We concentrated our translation on those aspects of the article dealing directly with NDI. The NDI Foundation thanks the researchers for their work toward understanding and more effectively treating this disorder.
© Copyright NDI Foundation 2007 (JC)
The function of V2R is to bind with AVP. This initiates a molecular sequence that allows the kidney to reabsorb water and concentrate urine. Faulty V2R, the result of a mutated V2R gene, is incapable of binding with VP, so the necessary molecular sequence resulting in urine concentration and body water balance does not occur.
The V2R lives in specific cell membranes (the thin layer encircling the cell, separating it from its environment). If you imagine the V2R as a beaded string, the majority of it lies within the cell membrane in seven folded clumps called transmembrane helices. Part of the receptor snakes outside the cell forming three curves called extracellular loops 1, 2, and 3. Part of it snakes inside the cell forming three curves called intracellular loops 1, 2, and 3. One end of the V2R, called the amino-terminus, is outside the cell with the extracellular loops. The other end of the V2R, called the carboxy-terminus, is inside the cell with the intracellular loops. (You can look at an example of V2R here.)
Tsukaguchi, et al., analyzed the V2R gene in two unrelated Japanese extended families and found two mutations of this gene that had never before been reported in the research literature. There are many types of mutations. The authors found a deletion mutation in the NDI patient from one family and a missense mutation in the NDI patient from the other family.
Genes are comprised of four simple nucleotide bases: adenine (A), cytosine (C), guanine (G) and thymine (T). These bases are linked together in specific sequences (according to what gene it is) by sugar and phosphate side bars. For example, part of one gene sequence might look like this, TCCGCACATCAC. The cells read these bases in sets of three, e.g. TCC, then GCA, then CAT, then CAC. Each set of three is called a codon, and each codon produces a single amino acid. The amino acids produced by the gene's codons combine to form a protein, in this case, the V2R. If the genetic sequence represented by the gene's nucleotide bases is disturbed, the gene may produce a faulty protein, in this case, a defective V2R.
The single deletion mutation in the first NDI patient was a single amino acid deletion at either codon 278 or 299 located in the sixth transmembrane helix. The missense mutation in the second NDI patient changed codon 143 in the second intracellular domain so that it produced a different amino acid than normal, which means the structure of the V2R produced would be different than normal. This is important because if the structure of the V2R is altered, it may not be able to bind with AVP.
The authors note that the amino acid deletion in the sixth transmembrane helix could affect the V2R's ability to bind with AVP by altering the structure of the transmembrane helix. Or it could interfere with intracellular signaling by altering the proper protein structure of the carboxy terminus. The missense mutation, because it results in an altered V2R structure, may inhibit the V2R from either coupling with a G protein or activating a GDP/GTP exchange, two necessary steps in the molecular sequence leading to urine concentration and water reabsorption.
The authors analyzed the V2R genes of family members of the two NDI patients and found those who exhibited symptoms of NDI in the first family had the same V2R mutation as the first patient, and those who exhibited symptoms in the second family had the same V2R mutation as the second patient. Those who did not exhibit symptoms did not have mutated V2R genes.
NDI caused by mutated V2R genes is carried by the female, who is less likely to express the disorder's symptoms. And though it can be passed on to either the female or male offspring, it is the male who is more likely to express the symptoms. The female, if she inherits the defective gene, will become a carrier who then has a chance of passing it on to her offspring. The families studied by Tsukaguchi, et al., fit this pattern. The authors state the step that is needed to determine if these two mutated V2Rs are the cause of the respective patients' NDI is to express the mutant V2Rs in laboratory cell cultures and test their functional abilities.