Diabetes insipidus is primarily caused by the hyposecretion or inadequate release of antidiuretic hormone (ADH), also known as vasopressin. ADH is responsible for regulating water balance by promoting water reabsorption in the kidneys.

Incorrect choices:

a. This choice is incorrect. Overproduction of ADH would lead to excessive water reabsorption and concentrated urine, which is not characteristic of diabetes insipidus.

c. This choice is incorrect. Hypersecretion of aldosterone would lead to sodium retention and increased fluid volume, which is not characteristic of diabetes insipidus.

d. This choice is incorrect. Impaired function of the thyroid gland would lead to thyroid-related disorders, not diabetes insipidus.