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Defects in genes mediating thyroid hormone biosynthesis result in dyshormonogenic congenital hypothyroidism (CH). Here, we report homozygous truncating mutations in SLC26A7 in 6 unrelated families with goitrous CH and show that goitrous hypothyroidism also occurs in Slc26a7-null mice. In both species, the gene is expressed predominantly in the thyroid gland, and loss of function is associated with impaired availability of iodine for thyroid hormone synthesis, partially corrected in mice by iodine supplementation. SLC26A7 is a member of the same transporter family as SLC26A4 (pendrin), an anion exchanger with affinity for iodide and chloride (among others), whose gene mutations cause congenital deafness and dyshormonogenic goiter. However, in contrast to pendrin, SLC26A7 does not mediate cellular iodide efflux and hearing in affected individuals is normal. We delineate a hitherto unrecognized role for SLC26A7 in thyroid hormone biosynthesis, for which the mechanism remains unclear.

Pentavalent 99 Tc m -dimercaptosuccinic acid ( 99 Tc m -(V)DMSA) has established uses in the detection and diagnosis of medullary thyroid carcinoma, osteosarcoma, amyloidosis and many soft tissue tumours, but is not readily available as a commercial kit. We have evaluated published methods for preparation of 99 Tc m -(V)DMSA that are based on the modification of 99 Tc m -(III)DMSA commercial kits. The criteria for assessment were achievement of satisfactory radiochemical purity and practical considerations regarding the ease of synthesis. Quantification of the desired product's activity was achieved via thin-layer chromatography (silica gel) with an n-butanol:acetic acid:water solvent system. The developed plates were imaged on a gamma camera and analysed using standard software. The methods investigated were designated as Birmingham, Cambridge and Canterbury: the latter two were very similar. With experience, the methods eventually produced similar radiochemical purities of > 90%. However, the Birmingham method was found to be more satisfactorv in terms of its reliabilitv and simplicity of synthesis.

In a pilot study of consistency in nuclear medicine reporting, a panel of three observers evaluated 60 bone scans carried out for detection of metastases. The bone scans had originated from 10 departments. Difficulties arose in evaluation of the quality of the images by the panel members because of the differing criteria each chose to adopt. This highlights the need to define strictly, in advance, the parameters to be included in quality assessment. All three panel members agreed on the lesions present in 54 out of 60 studies. The observers' consensus report showed material differences from the original departmental report in the number of lesions present in 10 out of 60 studies. Material differences in the interpretation of the study occurred between panel members in two cases and between the panel and the original report in four cases. The pilot study has shown an acceptable level of consistency in bone scan reporting in the departments contributing images. A national study assessing consistency of reporting would be difficult to organize but alternative, more local, schemes are suggested.

A questionnaire was sent to all the estimated 200 hospital departments providing nuclear medicine imaging services in the UK. Replies were received from 162 (81%). The questionnaire was brief, but covered a wide range of aspects of a nuclear medicine service. While all responses showed departments to have some quality control procedures in operation, they were often not used correctly. In most departments there appears to be scope for improvement so that departmental managers can monitor more closely the quality of service provided.

125I emits no β rays but part of its soft γ radiation is transformed into low energy electrons. Considering the short tissue path length (2-5 μm) of these electrons, it was postulated that its radiation effect on the thyroid might be different from that of 131I (path length 2000 μm). An experiment was designed to compare the biological effect of several dose levels of radiation from 125I on the rat thyroid gland with that from 131I. The effect of varying doses of each isotope on goitrogenesis (methylthiouracil induced) and on thyroid/serum radioiodide concentration (T/S) ratio was measured in animals radiated while on either a normal or a low iodide diet. In relation to 131I, the effect of 125I on goitrogenesis generally was much less than its effect on function. The low iodide diet group given 125I, surprisingly, showed markedly less inhibition of goitrogenesis than the normal diet group, an opposite effect to that attained with 131I. We suggest that the observed differences are due to the gradient of energy absorption in the follicular cell from irradiation from 125I stored in the colloid. The apical cytoplasm would absorb much more energy than the basal cytoplasm and the nucleus, in contrast to the uniform absorption of energy from 131I across the cell. The comparatively lower effect of 125I on goitrogenesis, and the paradoxical reduction in its effect in the low iodide diet groups, may be due to the low energy absorption by the nucleus, especially when, in a taller cell, the nucleus is farther from the colloid.

Images Figure 1

Papillary and follicular thyroid carcinomas show a different pattern of ras oncogene mutation