Clinical Endocrinology (2016) 84, 149–153

LETTERS TO THE EDITOR

Graves’ disease and Gitelman syndrome Dear Editor, We read with great interest the letter to the editor entitled ‘Coexistence of Graves’ disease in a 14-year-old young girl with Gitelman syndrome’ by Zha et al.1 in a recent issue of Clinical Endocrinology. We have cared for three Japanese patients with genetically confirmed Gitelman syndrome (GS) complicated by Graves’ disease (GD). The clinical characteristics at diagnosis of GS and GD as well as the genetic analysis results for SLC12A3 of these patients are listed in Table 1. SLC12A3 codes thiazide-sensitive sodium chloride cotransporter in the early distal tubule in the kidney and is the gene most commonly responsible for Gitelman syndrome. All 3 of our patients were women, and the age at diagnosis of GD ranged from 17 to 56 years. Sustained and unexplained hypokalaemia without hypertension was the initial feature raising clinical suspicion of GS. They had normo- or hypomagnesaemia and hypocalciuria and underwent genetic analysis of SLC12A3. Patient 1 had visited another hospital for evaluation of diffuse goitre and palpitations and was diagnosed with GD. She began treatment with methimazole, but was switched to propylthiouracil because of skin eruption. After moving, she transferred to our clinic at the age of 18. Patient 2 had initially visited our clinic because of palpitations. She was diagnosed with GD and began treatment with methimazole. Patient 3 had presented with finger tremor.She was diagnosed with GD and underwent I-131 therapy followed by replacement of LT4 for postablative hypothyroidism. Hypokalaemia persisted during more than 2 years of follow-up even after the treatment of hyperthyroidism in all three patients. The prevalence of GS is estimated to be 1 in 40 000, and the estimated prevalence of heterozygous subjects with one of the genetic mutations that cause GS is at least one per cent in Caucasian populations.2 The actual prevalence of GS might be much higher in the Japanese population.3 There are large variations in the severity of clinical manifestations among patients with GS. Correlations between

the position or nature of SLC12A3 mutations and the severity of clinical manifestations are not apparent.4 Some patients are asymptomatic or develop only mild weakness, whereas others show severe neuromuscular symptoms such as generalized weakness. Considerable numbers of GS patients with mild symptoms are presumably not diagnosed precisely because genetic testing is not widespread and renal clearance studies using furosemide and thiazide are cumbersome. Hypokalaemia is the characteristic abnormality of GS on routine clinical laboratory tests. Although hypokalaemia is generally mild in patients with GS, some develop severe manifestations, such as hypokalaemic periodic paralysis. On the other hand, thyrotoxicosis is the most common cause of hypokalaemic periodic paralysis in GD, especially in Asian men. As the prevalence of GS is not necessarily low, clinicians need to be aware of GS as one of the possible causes of hypokalaemia in patients with GD.1,5

Sources of funding None to declare.

Conflict of interest None to declare. Tetsuya Mizokami*, Akira Hishinuma†, Takahiko Kogai†, Katsuhiko Hamada*, Tetsushi Maruta*, Kiichiro Higashi* and Junichi Tajiri* *Tajiri Thyroid Clinic, Kumamoto, †Department of Infection Control and Clinical Laboratory Medicine, Dokkyo Medical University, Tochigi, Japan E-mail: [email protected] doi: 10.1111/cen.12829

Table 1. Patient characteristics Gitelman syndrome

Graves’ disease

SLC12A3

K

Mg

(mmol/l) (RR: 35–53)

(mmol/l) (058–107)

U-Ca/creat (005–015)

Patient

Age

(Site of mutation)

1

18

Thr339Pro/

32

086

Graves' disease and Gitelman syndrome.

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