Nystagmus in a female carrier of ocular albinism.

account for the phenotypic variability in these cases would be the expression of recessive genes present on the hemizygous segments of the normal chromosome 18. Our patient clearly had some thyroid tissue, as indicated by physical examination and the presence of some 13"I accumulation in the neck. But whether the hypothyroidism is a result of a structural malformation in the gland or a defect in thyroxine synthesis was unfortunately not completely resolved before therapy was initiated. However, the presence of a striking difference between her protein-bound iodine (51 Htg/1OO ml) and her serum thyroxine (0-3 p,g/100 ml) suggests that she was synthesizing an abnormal iodinated peptide. Such a defect in thyroxine synthesis might result from the action of a recessive gene on the hemizygous portion of her normal chromosome 18. The coincidence in 3 patients, including the present case, of hypothyroidism with loss of genetic material from chromosome 18 suggests that at least one gene responsible for thyroid function may be located on this chromosome. The significance of the abnormal dermatoglyphics in several members of this family is not clear.