Nephrogenic diabetes insipidus overview

# Overview
Diabetes insipidus is the excretion of abnormally large volumes (i.e., >50 mL/kg body weight in 24 hours) of dilute urine (i.e., specific gravity <1.010 or osmolality <300 mOsm/kg).

# Pathophysiology
Nephrogenic diabetes insipidus (NDI) is characterized by inability to concentrate the urine, which results in polyuria (excessive urine production) and polydipsia (excessive thirst). Affected untreated infants usually have poor feeding and failure to thrive, and rapid onset of severe dehydration with illness, hot environment, or the withholding of water. Short stature and secondary dilatation of the ureters and bladder from the high urine volume is common in untreated individuals.

# Diagnosis
The clinical diagnosis of NDI relies upon demonstration of subnormal ability to concentrate the urine despite the presence of the antidiuretic hormone, pituitary-derived arginine vasopressin (AVP). The two genes associated with NDI are AVPR2 (X-linked) and AQP2 (autosomal recessive and autosomal dominant). Molecular genetic testing of the AVPR2 gene detects approximately 95% of disease-causing mutations in individuals with X-linked NDI; molecular genetic testing of the AQP2 gene detects about 95% of disease-causing mutations in individuals with autosomal recessive NDI. Such testing is clinically available.

# Treatment
Management by a team (nutritionist, pediatric nephrologist / endocrinologist, clinical geneticist); provide free access to drinking water and to toilet facilities; reduce polyuria (and thus polydipsia) up to 50% without inducing hypernatremia by use of one of the following: thiazide diuretics (i.e., hydrochlorothiazide, chlorothiazide), dietary restriction of sodium, nonsteroidal anti-inflammatory drugs (NSAIDs); in individuals with dehydration or shock, establish whether the deficit is primarily in free water (through water deprivation or excessive urine, stool, or sweat) or in extracellular fluid (bleeding, fluid extravasation) to avoid inappropriate treatment of dehydration with normal saline (0.9% NaCl); treat hydronephrosis, hydroureter, and megacystis with medical management to reduce urine output and continuous or intermittent bladder catheterization when post-void urinary bladder residuals are significant; when 'NPO' (nothing per ora), individuals with NDI must have intravenous replacement of their usual oral intake of water as 2.5% dextrose in water. Surveillance: monitoring of growth in infants and children; periodic measurement of serum sodium concentration to identify unrecognized hyperosmolality and early dehydration; annual renal ultrasound evaluation to monitor for hydronephrosis and megacystis.

# Prevention
- Agents/circumstances to avoid: Restriction of water intake. Testing of relatives at risk: evaluation of at-risk infants as early as possible to allow for prompt diagnosis and treatment to reduce morbidity from hypernatremia, dehydration, and dilation of the urinary tract.
- Genetic counseling: NDI is most commonly inherited in an X-linked manner (~90% of individuals). NDI can also be inherited in an autosomal recessive manner (~9% of individuals) or in an autosomal dominant manner (~1% of individuals). The risks to sibs and offspring depend upon the mode of inheritance and the carrier status of the parents, which can be established in most families using molecular genetic testing. Prenatal testing is available for at-risk pregnancies in which the disease-causing mutation(s) have been identified in an affected family member.