Familial dysalbuminemic hyperthyroxinemia: cumulative experience in 29 consecutive patients

Assessing the clinical and molecular diagnosis of inherited forms of impaired sensitivity to thyroid hormone from a single tertiary center

AIM

Resistance to thyroid hormone (RTH), characterized by persistent hyperthyroxinemia with non-suppressed thyrotropin (TSH), is mostly caused by mutations in thyroid hormone receptor beta gene (THRB). Two differential diagnoses should be considered due to similar clinical and laboratory findings: TSH-producing pituitary adenoma (TPA) and Familial Dysalbuminemic Hyperthyroxinemia (FDH). The aim of this study is to describe our single tertiary center experience in the molecular diagnosis of RTH in Brazilian patients, analyzing their clinical and laboratory characteristics and the most common differential diagnosis.

SUBJECTS AND METHODS

We enrolled 30 subjects with clinical and laboratory features of RTH. Patient´s evaluations included clinical examination, thyroid hormone profile and imaging tests. Sequencing analysis for THRB hot spot region was conducted on all patients, and those without mutations in beta isoform of the thyroid hormone receptor (TRβ) (non-TR-RTH) were investigated for albumin gene (ALB) mutation.

RESULTS

Seventeen patients presented mutations in TRβ (RTHβ); six were non-TR-RTH, three had a diagnosis of FDH with a mutation in ALB, and four were diagnosed with TPA. Two characteristics were different to what is commonly described in the literature: higher serum TSH levels in RTHβ patients when compared to the non-TR-RTH group, but this difference did not extend to free T4 (FT4) level; also the percentage of non-TR-RTH was higher than what was reported in other series.

CONCLUSION

In the present series, most cases were RTHβ with higher levels of TSH. We described three novel mutations in THRB (p.M313V, p.R320G and p.R438P) and the first patients with FDH molecular diagnosis (p.R242H) documented in Brazil.

A semiquantitative metric for evaluating clinical actionability of incidental or secondary findings from genome-scale sequencing

PURPOSE

As genome-scale sequencing is increasingly applied in clinical scenarios, a wide variety of genomic findings will be discovered as secondary or incidental findings, and there is debate about how they should be handled. The clinical actionability of such findings varies, necessitating standardized frameworks for a priori decision making about their analysis.

METHODS

We established a semiquantitative metric to assess five elements of actionability: severity and likelihood of the disease outcome, efficacy and burden of intervention, and knowledge base, with a total score from 0 to 15.

RESULTS

The semiquantitative metric was applied to a list of putative actionable conditions, the list of genes recommended by the American College of Medical Genetics and Genomics (ACMG) for return when deleterious variants are discovered as secondary/incidental findings, and a random sample of 1,000 genes. Scores from the list of putative actionable conditions (median = 12) and the ACMG list (median = 11) were both statistically different than the randomly selected genes (median = 7) (P < 0.0001, two-tailed Mann-Whitney test).

CONCLUSION

Gene-disease pairs having a score of 11 or higher represent the top quintile of actionability. The semiquantitative metric effectively assesses clinical actionability, promotes transparency, and may facilitate assessments of clinical actionability by various groups and in diverse contexts.Genet Med 18 5, 467-475.

Genetic determination of the hypothalamic-pituitary-thyroid axis: where do we stand?

For a long time it has been known that both hypo- and hyperthyroidism are associated with an increased risk of morbidity and mortality. In recent years, it has also become clear that minor variations in thyroid function, including subclinical dysfunction and variation in thyroid function within the reference range, can have important effects on clinical endpoints, such as bone mineral density, depression, metabolic syndrome, and cardiovascular mortality. Serum thyroid parameters show substantial interindividual variability, whereas the intraindividual variability lies within a narrow range. This suggests that every individual has a unique hypothalamus-pituitary-thyroid axis setpoint that is mainly determined by genetic factors, and this heritability has been estimated to be 40-60%. Various mutations in thyroid hormone pathway genes have been identified in persons with thyroid dysfunction or altered thyroid function tests. Because these causes are rare, many candidate gene and linkage studies have been performed over the years to identify more common variants (polymorphisms) associated with thyroid (dys)function, but only a limited number of consistent associations have been found. However, in the past 5 years, advances in genetic research have led to the identification of a large number of new candidate genes. In this review, we provide an overview of the current knowledge about the polygenic basis of thyroid (dys)function. This includes new candidate genes identified by genome-wide approaches, what insights these genes provide into the genetic basis of thyroid (dys)function, and which new techniques will help to further decipher the genetic basis of thyroid (dys)function in the near future.

Difficulties in diagnosing and managing coexisting primary hypothyroidism and resistance to thyroid hormone

OBJECTIVE

To report a case of resistance to thyroid hormone compounded by autoimmune primary hypothyroidism and to discuss the unusual pattern of results of thyroid function tests.

METHODS

A clinical case history is presented and illustrated with laboratory findings. The difficulty of monitoring the patient's response to levothyroxine supplement is also discussed, and relevant issues are addressed, including reviews of the literature.

RESULTS

A 45-year-old woman presented with longstanding and nonspecific symptoms of general anxiety and lethargy. Clinically, she was assessed to be euthyroid with no goiter. Her thyrotropin (thyroid-stimulating hormone or TSH) level was 43.6 (1/4)IU/mL, free thyroxine was 27.6 pmol/L, and free triiodothyronine was 7.8 pmol/L. Her anti-thyroid peroxidase titer was 1:102,400. Primary hypothyroidism was diagnosed, and treatment with 50 (1/4)g of levothyroxine daily was initiated, with progressive dose escalation. The patient, however, had thyrotoxic symptoms when her TSH was rendered "normal." The patient then discontinued her levothyroxine therapy, with a consequent elevation of her TSH level to 170.8 (1/4)IU/mL in conjunction with severe lethargy and lassitude. Biochemical evidence of metabolic disturbances was also present at the time, with hypercholesterolemia and elevated creatine kinase concentration. Rechallenge with levothyroxine resulted in considerable improvement in her biochemical findings and symptoms.

CONCLUSION

This patient has an interesting combination of autoimmune primary hypothyroidism and resistance to thyroid hormone. Levothyroxine replacement therapy was complicated by the nonspecificity of symptoms and the lack of an established TSH target value in this condition. Consideration should be given to using the affected family members' mean TSH level, when available, as a target guide for replacement therapy.