Balkan Journal of Medical Genetics

X-LINKED RECESSIVE FORM OF NEPHROGENIC DIABETES INSIPIDUS IN A 7-YEAR-OLD BOY
Janchevska A1,*, Tasic V1, Gucev Z1, Krstevska-Konstantinova M1, Cheong HI2,3,4
*Corresponding Author: Dr. Aleksandra Janchevska, Department of endocrinology and genetics, University Children’s Hospital Skopje, Medical Faculty, 1000 Skopje, Republic of Macedonia. Tel: +389-2-3147-474. Fax: +389-2-3129-027. E-mail: dr.sasha1969@yahoo.com
page: 81

CASE REPORT

We present the case of a 7-year-old boy, the third child in a family of healthy, non consanguineous parents. His two older sisters are also healthy. Our patient has a history of excretion of large amounts of dilute urine and polydipsia since infancy. He had several vomiting episodes with mild dehydration during the first 3 years of life. There was evidence of headaches, dizziness or visual problems. The boy drinks between 2 and 3 L/day and has 24-hour diuresis of 2 L. He has prepubertal appearance with an appropriate weight [+0.85 standard deviation score (SDS)], 75th percentile and height (+0.15 SDS), 50th percentile at the growth curve, for his age (Figure 1). His intelligence was also normal. Random serum sodium level was 154.0 mmol/L and serum osmolality was 296.0 mOsm/kg, but urine osmolality was 46.0 mOsm/kg. A measurement of AVP was not available and kidney ultrasound was uneventful. A water deprivation test showed very low urine osmolality after 8 hours of dehydration. After desmopressin administration, urine osmolality still remained low. Serum osmolality was in normal range for sex and age before and after desmopressin administration. Serum sodium values after water deprivation were also in upper normal range, 147.0 mmol/L. This indicates a nephrogenic form of diabetes insipidus. Molecular analyses showed two non synonymous variants (p.R106H and p.P286L) and both were inherited from his mother. The first is a hemizygous c.317G>A variant in exon 2 of AVPR2 [p.Arg(CGT)106His(CAT)], and the second is also a hemizygous c.857C>T variant in exon 2 of AVPR2 [p.Pro(CCC)286Leu(CTC)] (Figure 2). In silico analysis predicted that only p.P286L was a pathogenic mutation. Also, only the p.P286L mutation is known to have an evolutionary conserved residue. This non synonymous (missense) p.P286L mutation is pathogenic for our patient and results in clinically evident NDI. Treatment includes high volumes of liquids and low salt intake. These nonspecific measures are useful to avoid dehydration and to maintain adequate fluid balance.

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