Short Stature and Hypocalcuria


Question

I would like to ask about non-identical twin sisters, 20 yrs old, with "osteopenia" on DXA. However, their lower Z score (-2,0) is very likely due to their short stature (150 cm). They both have absolute and relative hypocalciuria (1,49 mmol urinary calcium per day, CCa/CCr 0,0048) with normal serum calcium, phosphorus, potassium, magnesium, creatinine, PTH, TSH and 25OH vitamin D levels. The pubertal development was normal and they both have regular menses.

Is there any link between "isolated" hypocalciuria and short stature? What else could be examined in adulthood? Best regards, K. Zajickova Institute of Endocrinology, Prague, Czech republic.

Response

- I would agree that the small height (4'11") may have a significant impact on the DEXA Z-score. It is somewhat difficult to assess the urinary calcium excretion in this setting. I assume the clearance values are in mmol/mmol. We often normalize 24-hr urine excretion to kg body weight, and I assume that she may also be of a relatively low weight. It would also be of use to know her dietary calcium intake as the value may be accounted for by a relatively low calcium diet. Rare disorders such as Gitelman's syndrome can present with hypocalciuria and decreased bone mass; hypomagnesemia and hypermagnesiuria are usually present. I also assume that such a patient may also be short because of chronic disease, alkalosis, and other electrolyte abnormalities. I am not aware of a specific syndrome of an otherwise healthy child with short stature and low dietary calcium excretion. Tom Carpenter, MD