A–13–year old boy is referred for evaluation of nocturnal enuresis and short stature. His blood pressure is normal. The hemoglobin level is 8g/dl.urea 112 mg/dl, creatinine 6 mg/dl, sodium 119 mEq/ dl, potassium 4 mEq/l, calcium 7 mg/dl, phosphate 6 mg/dl and alkaline phosphatase 300 U/I. Urinalysis shows trace proteinuria with hyaline casts; no red and white cells are seen. Ultrasound shows bilateral small kidneys and the micturating cystourethrogram is normal. The most likely diagnosis is –
Features seen in this 13 yr. old boy
Short Stature
Nocturnal enuresis
Normal B.P.
Reduced hemoglobin
Hyponatremia (N level in 136-145 meq/dl)
Hypocalcemia (N level is 9-10.5 mg/dl)
Normal potassium level (N is 3.5 to 5 meq/dl)
B/L small kidneys
Increased blood urea (N is 10 - 40 mg/dl)
Increased alkaline phosphates (N is upto 130 IU)
Increased serum creatinine (N is < 1.5 m g/dl)
This pt. gives a classical presentation of nephronophthisis, 

About other options
Alport syndrome

It can be easily ruled out as it presents with
Microscopic hematuria (first symptom)               
Proteinuria     
Sensorineural hearing loss      
b/l anterior lenticonus        

Medullary sponge kidney                                           

Easily ruled out as the kidneys are normal or increased is size in MSK and also the age of presentation is third or fourth decade.

Chronic glomerulonephritis

pts of CGN usually have heavy proteinuria, frank or occult hematuria and hypertension.
Alport's syndrome
Medullary sponge kidney.
Chronic glomerulonephritis.
Nephronophthisis