Clinical_Rounds_in_Endocrinology_Volume_II_-_Pediatric_Endocrinology

166

71. What are the adjuvant therapies in XLH?

Recombinant growth hormone has been tried to increase phosphate reabsorp-

tion in patients with X-linked hypophosphatemic rickets/osteomalacia; how-

ever, it has not been found to be beneficial. Calcimimetic agents like cinacalcet

have been used to treat secondary hyperparathyroidism associated with phos-

phate therapy. Use of cinacalcet has been shown to be effective in reducing the

doses of phosphate and calcitriol. Recently, use of intravenous iron therapy has

also been shown to be useful. Monoclonal antibodies against FGF-23 have been

shown to be effective in mouse models of X-linked hypophosphatemia.

72. What are the endocrine manifestations of renal tubular acidosis?

Renal tubular acidosis (RTA) is characterized by normal anion gap metabolic

acidosis with hypokalemia in the presence of normal glomerular filtration rate.

RTA may occur either due to the defect in reabsorption of HCO 3 - at proximal

tubule (proximal RTA, type 2) or defect in excretion of H+ ions at distal tubule

(distal RTA, type 1). The endocrine manifestations of RTA include growth fail-

ure, polyuria, rickets–osteomalacia, and nephrocalcinosis–nephrolithiasis. In

addition, type 4 RTA is characterized by normal anion gap metabolic acidosis

with hyperkalemia and normal or modestly reduced glomerular filtration rate.

73. What are the differences in clinical features of proximal and distal RTA?

The characteristic clinical features of proximal and distal RTA are summarized

in the table given below.

Parameters

Proximal RTA Distal RTA

(Type 2) (Type 1)

Pathogenesis Defect in reabsorption of

HCO 3 − at proximal tubule of

kidney

Defect in excretion of H+ ions

at distal tubule of kidney

Growth failure Often present Often present

Rickets–osteomalacia Often present Often present

Nephrocalcinosis–

nephrolithiasis

Absent Often present

Other tubular defects Common (Fanconi’s syndrome) Absent

Etiology Primary Primary

Secondary: Secondary:

Wilson disease Sjogren’s syndrome

Valproate Systemic lupus

Aminoglycoside erythematosus

Acetazolamide

74. Why is there rickets in RTA?

Rickets–osteomalacia is a characteristic feature of both proximal and distal RTA,

and the pathophysiological mechanisms for the development of rickets–osteoma-

5 Rickets–Osteomalacia