How is Raynaud's syndrome related to mixed connective tissue disease?

With Raynaud's syndrome, cold temperatures or an emotionally charged moment lead a person's fingers to become very pale or bluish and tingly or numb. Spasms in the blood vessels cause the flow of blood to the fingers, toes, nose and ears to be interrupted. Raynaud's syndrome is a common symptom of mixed connective tissue disease (MCTD) and is often the first symptom to present itself.