Deficiency of …………….. causes diabetes mellitus.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Diabetes Mellitus**: Diabetes mellitus is a metabolic disorder characterized by high blood sugar levels over a prolonged period. It is primarily caused by the body's inability to produce or effectively use insulin.

2. **Role of Insulin**: Insulin is a hormone produced by the pancreas that helps regulate blood glucose levels. It facilitates the uptake of glucose by cells, allowing them to use it for energy or store it for future use.

3. **Hyposecretion of Insulin**: The term "hyposecretion" refers to the insufficient secretion of a hormone. In the case of diabetes mellitus, hyposecretion of insulin means that the pancreas is not producing enough insulin.

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