a different step in the production of thyroid hormone. Among the conditions inherited this way are the following: A defect in the creation of the enzyme that produces thyroid hormone: (see Chapter 4): Patients with this condition are hypothyroid (see Chapter 5) and have goiters. Thyroid hormone unresponsiveness: If you inherit a bad gene instead of the gene that makes the receptor protein for thyroid hormone, your end organs aren’t responsive to the thyroid hormone your body produces. This condition causes patients to be deaf and have goiters. With this condition, the T3, T4, and TSH levels are all elevated (see Chapter 4). Pendred syndrome: Patients with this disease are deaf and have goiters, but their thyroid function is normal. The disease also causes mental retardation and an increased tendency to develop thyroid cancer. The defect is in the production of thyroid hormone, but at some point it improves so that hypothyroidism isn’t present later on. Thyroid transcription–factor defect: Patients have goiters and decreased levels of thyroglobulin. If you remember that transcription is the term for the production of messenger RNA from DNA, you understand that this defect arises from a failure to produce the enzyme necessary to make thyroid hormone. Defect in thyroid production: This disease is different from thyroid transcription–factor defect. Patients are hypothyroid, have goiters, and experience mental retardation. Lab tests show a defect in the formation of thyroid hormone. Normally, two molecules of tyrosine with iodine attached couple to form thyroid hormone, but this process fails in this particular inherited condition.
Dominant inheritance Many inherited thyroid conditions pass from parents to children through dominant inheritance: One “bad” gene produces the disease. These diseases tend to be more common than those inherited by recessive genes. Examples of diseases inherited this way are as follows: Thyroid hormone–receptor defects: A number of receptor defects are possible. With one of these conditions, your body is resistant to the action of thyroid hormones. At the same time, you experience mild hyperthyroidism. Patients with this condition have short stature, learning disabilities, deafness, and goiters. Lab tests show high levels of T3, T4, and TSH. These conditions are rare, resulting from a mutation in the gene responsible for the thyroid receptor. Another type of receptor defect produces a child with severe cretinism of the neurologic form (see Chapter 12). Papillary thyroid carcinoma (see Chapter 8). This type of cancer usually occurs at an earlier age than thyroid cancer that’s not inherited. Thyroid hormone resistance (also found in a recessive form). Patients with this