Wednesday, February 27, 2013

Topic Discussion: Genetic Diabetes Insipidus

The arginine vasopressin gene (AVP gene), the arginine vasopressin receptor 2 gene (AVPR2), and the vasopressin-sensitive water channel gene (aquaporin 2 [AQP2])—provide the basis for understanding of three different hereditary forms of “pure” diabetes insipidus: Neurohypophyseal diabetes insipidus, X-linked nephrogenic diabetes insipidus (NDI), and non–X-linked NDI(AD and AR), respectively. Four main categories can be considered. 

Neurohypophyseal diabetes insipidus: Autosomal Dominant, they retain some limited capacity to secrete AVP during severe dehydration, and the polyuro-polydipsic symptoms usually appear after the first year of life, when the infant’s demand for water is more likely to be understood by adults. 
Delayed onset of disease and can get worse with age.  The gene mostly involved is AVP gene. 
X-linked NDI: Affected male patients do not concentrate their urine after administration of AVP. Because this form is a rare, recessive X-linked disease, female individuals are unlikely to be affected, but heterozygous female individuals can exhibit variable degrees of polyuria and polydipsia because of skewed X chromosome inactivation.  The gene mostly involved is AVP2 gene. V2 receptors have been tried as chaperone medications as a trial to help overcome the misfolding that happens as a result of the gene mutation and helps in NDI.
Autosomal recessive NDI: Some cases have been identified. They have defect in the AQP2 gene.
AQP2 mutations that are responsible for autosomal recessive NDI are characterized by misrouting of the misfolded mutant proteins and are trapped in the endoplasmic reticulum.
Autosomal Dominant linked NDI: Both males and females affected. A patient who presented shortly after birth and it is a defect in the AQP2 channel gene. 

A nice review can be found at JASN and NDT

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