A nurse is reviewing the medical record of a newly admitted client who has major depressive disorder. Which of the following findings should the nurse identify as a risk factor for this condition?

A reason: The client has a serotonin deficiency. A serotonin deficiency is a known biological risk factor for major depressive disorder. Low levels of serotonin in the brain can contribute to depressive symptoms. B reason: The client has acute bronchitis. Acute bronchitis is a respiratory condition and is not a recognized risk factor for major depressive disorder. C reason: The client has an elevated calcium level. Elevated calcium levels can indicate hyperparathyroidism but are not specifically associated with an increased risk of major depressive disorder. D reason: The client is an only child. Being an only child is not a recognized risk factor for major depressive disorder. Risk factors are more commonly related to biological, psychological, and environmental factors.