Calcium, Phosphate, Magnesium

Question 1

PTHrP has a physiological function. What is this?

Answer 1

PTHrP is released by the mother to induce a mild hypercalcaemia in herself to liberate enough calcium in her blood to promote skeletal development in a foetus. Therefore PTHrP is unsuitable for measurement in pregnancy and breast feeding but is though to be the main mechanism of hypercalcaemia of malignancy

Question 2

What proportion of calcium is freely ionised and circulating?

Answer 2

1%

Question 3

Which electrolyte is always raised in parathyroid adenomas?

Answer 3

Calcium

Question 4

The following results are obtained:

Calcium adjusted: 1.9
Phosphate: 2.0
PTH: 71

What is the diagnosis and implicated gene?

Answer 4

Pseudohypoparathyroidism. It is rare, with appropriate elevations in PTH due to chronically low calcium but PTH resistance (G-protein defect).

GNAS1.

Question 5

The following results are obtained:

Calcium adjusted: 1.9
Phosphate: 0.7
PTH: 71

What is the diagnosis?

Answer 5

Vitamin D deficiency

Question 6

The following results are obtained:

Calcium: 2.4
Phosphate: 1.3
PTH: 3

The patient has a shortened blunt 4 and 5 metacarpal bone, is short, obese and suffers from osteomalacia cutis (bony deposits in skin). What is the diagnosis and from what parent is it inherited?

Answer 6

Pseudopseudohypoparathyroidism. This is the constellation of clinical findings as pseudohypoparathyroidism but without the biochemical findings.

Father