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condition have a goiter and begin to speak at a later than expected age but have normal thyroid function. Lab tests show that T3 and T4 levels are high, but the TSH level is normal. Multiple endocrine neoplasia, type II: This condition causes tumors on multiple organs, including the thyroid (see Chapter 8), the adrenal gland, and the parathyroid glands. Lab tests show increased levels of epinephrine and calcitonin in the blood. Medullary carcinoma of the thyroid, familial: Patients with this condition have medullary cancer (see Chapter 8).

X-linked inheritance X-linked inheritance presents fewer examples of thyroid disease because men have only one X chromosome, and women have two, compared to 44 other chromosomes that can produce a disease by recessive or dominant inheritance. If a disease passed on by the X chromosome is recessive, both parents must give the gene to a daughter in order for the disease to appear. But a son gets the disease if only one parent passes along the gene. Because Y chromosomes are only present in males, Y-linked inheritance is only found in males, and it’s rare because the Y chromosome is so small. Some examples of diseases inherited this way include Immunodeficiency and polyendocrinopathy: A baby with this condition has unmanageable diarrhea, diabetes, and thyroid autoimmune disease and usually dies very young. Thyroid-binding globulin abnormality: This condition produces retardation. Lab tests show that patients with this disease have decreased thyroid-binding globulin (see Chapter 3). Multinodular goiter: The thyroid is larger than normal and multinodular (see Chapter 9).

Inheriting a disease through multiple genes The major thyroid disease inherited as a result of abnormalities of multiple genes is autoimmune thyroiditis. This disease is much more common in women than in men, so you may assume that the inheritance is linked to the X chromosome somehow. But if this is the case, scientists don’t know the method by which the X chromosome passes the disease along. One idea is that the female sex hormone influences the occurrence of this disease, but scientists don’t understand just how this may happen. Autoimmune thyroiditis is easy to diagnose because lab tests show that a person has autoantibodies (see Chapter 5) that damage the thyroid. Many genes are involved in the production of autoantibodies. The substance (such as thyroid tissue) that provokes antibodies is called an

Thyroid for dummies  
Thyroid for dummies