Genotype-Phenotype Correlations in Thirty Japanese Patients with Congenital Hypothyroidism Attributable to TG Defects.

CONTEXT: Thyroglobulin (Tg), encoded by TG, is essential for thyroid hormone synthesis. TG defects result in congenital hypothyroidism (CH). Most reported patients were born before the introduction of newborn screening (NBS). OBJECTIVE: We aimed to clarify the phenotypic features of patients with TG defects diagnosed and treated since the neonatal period. SUBJECTS AND METHODS: We screened 1061 patients with CH for thirteen CH-related genes and identified thirty patients with TG defects. One patient was diagnosed due to hypothyroidism-related symptoms and the rest were diagnosed via NBS. Patients were divided into two groups according to their genotypes, and clinical characteristics were compared. We evaluated the functionality of the seven missense variants using HEK293 cells. RESULTS: Twenty-seven rare TG variants were detected, including fifteen nonsense, three frameshift, two splice-site, and seven missense variants. Patients were divided into two groups: thirteen patients with biallelic truncating variants and seventeen patients with monoallelic/biallelic missense variants. Patients with missense variants were more likely to develop thyroid enlargement with TSH stimulation than patients with biallelic truncating variants. Patients with biallelic truncating variants invariably required full hormone replacement, whereas patients with missense variants required variable doses of levothyroxine. Loss of function of the seven missense variants was confirmed in vitro. CONCLUSION: To our knowledge, this is the largest investigation on the clinical presentation of TG defects diagnosed in the neonatal period. Patients with missense variants showed relatively mild hypothyroidism with compensative goiter. Patients with only truncating variants showed minimal or no compensative goiter and required full hormone replacement.

Adult Thyroid Outcomes of Congenital Hypothyroidism.

Background: More than 40 years have passed since the introduction of newborn screening (NBS) for congenital hypothyroidism (CH), and many early diagnosed patients have reached adulthood. Their thyroid morphology and function have been little studied. This cross-sectional, observational study was conducted to characterize the thyroid morphology and function of adult CH patients diagnosed in the framework of NBS for CH. Methods: A total of 103 adult CH patients born after 1979 were enrolled at Ito Hospital, Tokyo, Japan, and were classified into Goiter, Normal gland, and Dysgenesis groups based on ultrasonographic findings. For 60 patients, genetic analysis was performed. Thyroid function test results and the proportion of patients with thyroid nodules were compared among the three groups and between 56 female CH patients and 168 non-CH women matched for thyrotropin levels. Results: A significantly low serum free triiodothyronine/free thyroxine ratio (0.22) was observed in the Dysgenesis group. Thyroid nodules were detected in 14.3% (8/56) of female CH patients, more frequently than in non-CH women. Thyroid nodules were detected most frequently in the Goiter group (71%, 10/14). Genetic defects were identified in 89% (8/9) of patients belonging to the Goiter group, including thyroglobulin defect (33%, 3/9), thyroid peroxidase defect (33%, 3/9), and dual oxidase 2 defect (22%, 2/9). Conclusions: Our results suggest that adults with thyroid dysgenesis on levothyroxine replacement therapy have relative triiodothyronine deficiency. Most adults with goitrous CH have genetic dyshormonogenesis. They are at high risk of developing thyroid nodules. Our findings support the current guideline recommendation that CH patients with dyshormonogenesis should undergo periodic thyroid ultrasonography.

Goiter in a 6-year-old patient with novel thyroglobulin gene variant (Gly145Glu) causing intracellular thyroglobulin transport disorder: Correlation between goiter size and the free T3 to free T4 ratio.

Thyroglobulin gene abnormalities cause thyroid dyshormonogenesis. A 6-yr-old boy of consanguineous parents presented with a large goiter and mild hypothyroidism (thyroid-stimulating hormone [TSH] 7.2 µIU/mL, free T3 [FT3] 3.4 pg/mL, free T4 [FT4] 0.6 ng/dL). Despite levothyroxine (LT4) administration and normal TSH levels, the goiter progressed slowly and increased rapidly in size at the onset of puberty. Thyroid scintigraphy revealed a remarkably high 123I uptake of 75.2%, with a serum thyroglobulin level of 13 ng/ml, which was disproportionately low for the goiter size. DNA sequencing revealed a novel homozygous missense variant, c.434G>A [p.Gly145Glu], in the thyroglobulin gene. Goiter growth was suppressed by increasing the LT4 dose. Thyroidectomy was performed at 17-yr-of-age. Thyroglobulin analysis of the thyroid tissue detected mutant thyroglobulin present in the endoplasmic reticulum, demonstrating that thyroglobulin transport from the endoplasmic reticulum to the Golgi apparatus was impaired by the Gly145Glu variant. During the clinical course, an elevated FT3/FT4 ratio was observed along with thyroid enlargement. A high FT3/FT4 ratio and goiter seemed to be compensatory responses to impaired hormone synthesis. Thyroglobulin defects with goiter should be treated with LT4, even if TSH levels are normal.

A case of hypoparathyroidism, deafness, and renal dysplasia (HDR) syndrome with a novel frameshift variant in GATA3, p.W10Cfs40, lacks kidney malformation.

Autosomal dominant hypoparathyroidism, deafness, and renal dysplasia (HDR) syndrome are typically diagnosed by manifestations of the three features with a positive family history. Our case carried a de novo variant in causative gene, GATA3, but presenting no renal dysplasia or family history. The phenotypic heterogeneity raises a caution for diagnosis.

A Japanese Family with DICER1 Syndrome Found in Childhood-Onset Multinodular Goitre.

INTRODUCTION: Germline DICER1 mutations have recently been identified in familial multinodular goitre (MNG). The natural history of thyroid nodules in DICER1 carriers in children is unclear. The purpose of this study was to describe the clinical and genetic findings of childhood-onset MNG with DICER1 carrier in a patient who underwent total thyroidectomy. CASE PRESENTATION: The 6-year-old proband had a thyroid nodule, and the number and size of nodules increased over 3 years. A total thyroidectomy was chosen because of the rapid rise in thyroglobulin levels, discomfort when swallowing, and the mother's history of poorly differentiated thyroid cancer (PDTC). Histopathology revealed adenomatous goitre without malignant cells. Her mother, maternal aunt, and maternal grandmother also had thyroid nodules removed during adolescence. Also, her mother had PDTC with lung metastases, and her maternal aunt had an ovarian germ cell tumour. DICER1 mutation analysis identified a heterozygous novel nonsense mutation (c.4509C>G, p.Y1503X) for the patient, her mother, her maternal grandmother, and her asymptomatic elder brother. Y1503X was identified in all resected thyroid tissues, while heterozygous D1709G, D1810V, and E1813K mutations were identified in individual nodules. DISCUSSION/CONCLUSION: A thyroid nodule was detected in chemotherapy- or radiotherapy-naïve patient with DICER1 carrier aged 6 years, and MNG developed over 3 years. This pedigree highlights the natural history of nodular disease in DICER1 carriers and identifies a possible association between DICER1 and more aggressive malignancies.

Genetic alteration of ARMC5 in a patient diagnosed with meningioma and primary macronodular adrenal hyperplasia: a case report.

A monoallelic germline alteration of ARMC5 causes primary bilateral macronodular adrenal hyperplasia (PBMAH) with Cushing's syndrome via its subsequent somatic alteration on the other allele as the second hit. PBMAH is sometimes complicated with meningioma. Dependency of such a multi-organ disease on the second hit mechanism was reported before, but this finding has not been confirmed yet. We describe a case of a 65-year-old female with PBMAH, carrying a heterozygous germline alteration of ARMC5, p.R267*, complicated with meningioma associated with somatic loss of heterozygosity (LOH) of the unaffected allele. Pathogenic alterations of ARMC5 may also contribute to the development of meningioma by the two-hit mechanism.

A CASE OF FAMILIAL NONAUTOIMMUNE HYPERTHYROIDISM DURING PREGNANCY.

OBJECTIVE: Familial nonautoimmune hyperthyroidism (FNAH) is a rare disease. To date there are few, if any, reports of pregnancies in women with FNAH. Our objective here is to present such a case. METHODS: Free thyroxine (free T4), free triiodothyronine (free T3), thyroid-stimulating hormone (TSH), and antibodies related to the thyroid were measured. Fetal thyroid function indicators including thyroid volume and ossification were checked using ultrasound. Thyroid-stimulating hormone receptor (TSHR) gene analyses were performed. RESULTS: The patient was a 30-year-old woman with no past medical history. She was introduced to our hospital in the fifth gestational week for pregnancy care because her family history revealed that her mother had nonautoimmune hyperthyroidism with a TSHR-activating germ-line mutation (Asn406Ser). The serum free T4 was 1.88 ng/dL (normal, 0.62 to 1.19 ng/dL), free T3 was 3.27 pg/mL (normal, 2.55 to 3.88 pg/mL), TSH was 0.02 µIU/mL (normal, 0.007 to 3.619 µIU/mL), and TSHR was negative which were considered to be consistent with mild primary hyperthyroidism. Serum free T4, free T3, and TSH concentrations were monitored every 4 to 6 weeks with a peak free T4 of 2.23 ng/dL noted at gestational week 9. The patient had no signs related to hyperthyroidism throughout pregnancy. The patient delivered a 3,518 g girl at 40 weeks of gestation. Genetic analysis of her TSHR gene showed heterozygous Asn406Ser mutation. The offspring did not show any signs of prenatal hyperthyroidism, and thyroid function at day 6 after delivery revealed a free T4 of 2.41 ng/dL (normal, 1.83 to 2.91 ng/dL) and a TSH of 3.55 µIU/mL (normal, 0.51 to 4.57 µIU/mL). CONCLUSION: Women with FNAH and mild thyrotoxicosis prior to pregnancy may have continuous hyperthyroidism with additional change due to the series of human chorionic gonadotropin secretion during pregnancy.

Painless destructive thyroiditis in a patient with resistance to thyroid hormone: a case report.

BACKGROUND: Resistance to thyroid hormone (RTH) usually features a syndrome of inappropriate secretion of thyroid-stimulating hormone (SITSH) without suppression of the typical high thyroid hormone levels. However, some patients with RTH show thyroid-stimulating hormone (TSH) suppression due to thyrotoxicosis. We report a case of painless thyroiditis in a patient with RTH that was misdiagnosed as Graves' disease because of TSH-suppressed thyrotoxicosis. CASE PRESENTATION: A sixteen-year-old boy consulted a local general physician for fatigue. He had a goiter, and biochemical analysis showed TSH < 0.1 µIU/mL, free triiodothyronine (FT3) of 2.70 pg/mL, and free thyroxine (FT4) of 3.6 ng/dL. He was diagnosed with Graves' disease and was treated with 20 mg thiamazole. One year later, he was referred to the department of endocrinology because of SITSH. He was finally diagnosed with RTH due to the finding of a heterozygous missense mutation (methionine 334 threonine) in the thyroid hormone receptor ß gene. Three years after cessation of thiamazole, his hyperthyroxinemia showed marked exacerbation with TSH suppression. We diagnosed him with painless destructive thyroiditis because of low technetium-99 m (Tc-99 m) uptake in the thyroid. Extreme hyperthyroxinemia was ameliorated, with a return to the usual SITSH levels, within 1 month without any treatment. CONCLUSION: The present case demonstrates that diagnosing RTH is difficult when patients show hyperthyroxinemia with complete suppression of TSH to undetectable levels, and the data lead to misdiagnosis of RTH as Graves' disease. The initial diagnosis is important, and Tc-99 m scintigraphy is useful for the differential diagnosis of thyrotoxicosis accompanying RTH.

Congenital Primary Hypothyroidism with the Homozygous Nonsense Mutation P.K1374* in the Thyroglobulin Gene and a Normal-sized Thyroid Gland on Levothyroxine Replacement.

Thyroglobulin (TG) gene mutations cause thyroid dyshormonogenesis, which is typically associated with a congenital goiter. We herein report the case of a 64-year-old man with congenital primary hypothyroidism who had a normal-sized thyroid gland on levothyroxine replacement. He had short stature (-3.1 standard deviations) and mild intellectual impairment. Thyroid autoantibodies were all negative, and the serum TG levels were undetectable. Eventually, he was found to have the novel homozygous nonsense mutation p.K1374* in the TG gene. The possibility of TG mutation should be considered for patients with congenital primary hypothyroidism and a very low serum TG level, regardless of the thyroid size.

Seasonal Changes in Serum Thyrotropin Concentrations Observed from Big Data Obtained During Six Consecutive Years from 2010 to 2015 at a Single Hospital in Japan.

BACKGROUND: This study analyzed big data for serum thyrotropin (TSH), free triiodothyronine (fT3), and free thyroxine (fT4) concentrations in patients who had attended the outpatient clinic of Ito Hospital (Tokyo, Japan) during a recent six-year period (between January 1, 2010, and December 31, 2015) in order to investigate for seasonal changes. METHODS: The serum TSH concentrations were reviewed for all 135,417 patients aged >20 years. Patients with any thyroid diseases were included, irrespective of whether they were receiving drug therapy. In total 1,637,721 serum samples were analyzed for TSH, 1,626,269 for fT3, and 1,669,381 for fT4. RESULTS: It was observed that the TSH concentrations showed annual changes during the six-year period. They decreased during the summer, while they increased during the winter. The TSH concentrations were negatively correlated with the daily temperatures (Spearman rank correlation coefficient -0.4486; p < 0.0001). The same applied for the correlation between fT3 concentrations and daily temperatures. CONCLUSIONS: The fact that the TSH concentrations show annual changes in areas where the temperature ranges during the year are rather wide should be borne in mind for interpretation of results.

Standardization of Free Thyroxine Measurements Allows the Adoption of a More Uniform Reference Interval.

BACKGROUND: The IFCC Committee for Standardization of Thyroid Function Tests intended to standardize free thyroxine (FT4) immunoassays. We developed a Système International d'Unités traceable conventional reference measurement procedure (RMP) based on equilibrium dialysis and mass spectrometry. We describe here the latest studies intended to recalibrate against the RMP and supply a proof of concept, which should allow continued standardization efforts. METHODS: We used the RMP to target the standardization and reference interval (RI) panels, which were also measured by 13 manufacturers. We validated the suitability of the recalibrated results to meet specifications for bias (3.3%) and total error (8.0%) determined from biological variation. However, because these specifications were stringent, we expanded them to 10% and 13%, respectively. The results for the RI panel were reported as if the assays were recalibrated. We estimated all but 1 RI using parametric statistical procedures and hypothesized that the RI determined by the RMP was suitable for use by the recalibrated assays. RESULTS: Twelve of 13 recalibrated assays had a bias, meeting the 10% specification with 95% confidence; for 7 assays, this applied even for the 3.3% specification. Only 1 assay met the 13% total error specification. Recalibration reduced the CV of the assay means for the standardization panel from 13% to 5%. The proof-of-concept study confirmed our hypothesis regarding the RI but within constraints. CONCLUSIONS: Recalibration to the RMP significantly reduced the FT4 immunoassays' bias, so that the RI determined by the RMP was suitable for common use within a margin of 12.5%.

Harmonization of Serum Thyroid-Stimulating Hormone Measurements Paves the Way for the Adoption of a More Uniform Reference Interval.

BACKGROUND: The IFCC Committee for Standardization of Thyroid Function Tests developed a global harmonization approach for thyroid-stimulating hormone measurements. It is based on a multiassay method comparison study with clinical serum samples and target setting with a robust factor analysis method. Here we describe the Phase IV method comparison and reference interval (RI) studies conducted with the objective to recalibrate the participating assays and demonstrate the proof-of-concept. METHODS: Fourteen manufacturers measured the harmonization and RI panel; 4 of them quantified the harmonization and first follow-up panel in parallel. All recalibrated their assays to the statistically inferred targets. For validation, we used desirable specifications from the biological variation for the bias and total error (TE). The RI measurements were done with the assays' current calibrators, but data were also reported after transformation to the new calibration status. We estimated the pre- and postrecalibration RIs with a nonparametric bootstrap procedure. RESULTS: After recalibration, 14 of 15 assays met the bias specification with 95% confidence; 8 assays complied with the TE specification. The CV of the assay means for the harmonization panel was reduced from 9.5% to 4.2%. The RI study showed improved uniformity after recalibration: the ranges (i.e., maximum differences) exhibited by the assay-specific 2.5th, 50th, and 97.5th percentile estimates were reduced from 0.27, 0.89, and 2.13 mIU/L to 0.12, 0.29, and 0.77 mIU/L. CONCLUSIONS: We showed that harmonization increased the agreement of results from the participating immunoassays, and may allow them to adopt a more uniform RI in the future.

A Novel Germline Mutation of KEAP1 (R483H) Associated with a Non-Toxic Multinodular Goiter.

BACKGROUND: A germline mutation of KEAP1 gene was reported as a novel genetic abnormality associated with familial multinodular goiter. That report was limited, and the pathogenic features were not well established. PATIENT FINDINGS: We report a 47-year-old Japanese woman who presented with hyperthyroidism and a large multinodular goiter. The family history was notable for a paternal history of goiter. Graves' disease was diagnosed based on positive TRAb, but scintiscan imaging showed that the patient's radioiodine uptake was restricted in the non-nodular areas, indicating largely cold nodules. A total thyroidectomy was performed. The resected thyroid tissue weighed 209 g, and subsequent pathological findings were benign. The patient had a germline heterozygous KEAP1 mutation, c. 1448 G > A, resulting in an amino acid substitution (p.R483H). A next-generation sequencing analysis covering all known genes associated with multinodular goiter showed no additional germline mutation. The nuclear accumulation of NRF2, a protein associated with KEAP1, was shown at much higher rates in the patient's nodules compared with nodules obtained from four unrelated patients with multinodular goiters. CONCLUSION: A novel germline mutation (R483H) of KEAP1 gene was associated with the development of a non-toxic multinodular goiter.

Iodide Transport Defect and Breast Milk Iodine.

BACKGROUND: Iodide transport defect (ITD) is a dyshormonogenetic congenital hypothyroidism caused by sodium/iodide symporter (NIS) gene mutations. In the lactating mammary gland, iodide is concentrated by NIS, and iodine for thyroid hormone synthesis is thereby supplied to the infant in the breast milk. CASE DESCRIPTION: A 34-year-old Japanese woman was diagnosed with ITD caused by a homozygous NIS gene mutation T354P. She had begun treatment of primary hypothyroidism with levothyroxine at the age of 5. She delivered a baby at the age of 36. The iodine concentration in her breast milk was 54 µg/l. She took a 50-mg potassium iodide tablet daily to supply iodine in the breast milk, starting on the 5th day postpartum. Her breast milk iodine concentration increased to 90 µg/l (slightly above the minimum requirement level). The patient weaned her baby and stopped taking the daily potassium iodide tablet 6 weeks postpartum, and the baby began to be fed with relatively iodine-rich formula milk. The baby's thyroid function remained normal from birth until 6 months of age. CONCLUSION: Possible iodine deficiency in the infant breast-fed by an ITD patient should be kept in mind. Prophylactic iodine supplementation is essential for such infants in order to prevent severe iodine deficiency.

Breakthrough viridans streptococcal bacteremia in allogeneic hematopoietic stem cell transplant recipients receiving levofloxacin prophylaxis in a Japanese hospital.

BACKGROUND: Breakthrough viridans streptococcal bacteremia (VSB) in patients with hematological malignancy receiving levofloxacin prophylaxis is a major blood stream infection (BSI) occurring during febrile neutropenia. However, clinical data focused on VSB in allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients are lacking. METHODS: The medical records of allo-HSCT recipients who received oral levofloxacin prophylaxis between January 2011 and August 2013 at Toranomon Hospital were reviewed to evaluate breakthrough VSB. Stored viridans streptococcal (VGS) species were identified by using sodA gene sequencing, and were assessed for drug susceptibility. RESULTS: Among the 184 allo-HSCT recipients on levofloxacin prophylaxis, 28 (15.2 %) experienced breakthrough VSB. All of the 28 recipients with VSB were treated with a cefepime-based or piperacillin/tazobactam-based regimen. The susceptibility rates of the VGS strains for levofloxacin, cefepime, piperacillin/tazobactam, meropenem, and vancomycin were 0 %, 95 %, 100 %, 100 %, and 100 %, respectively. Both the MIC50 (minimum inhibitory concentration) and the MIC90 of ceftazidim (0.5 µg/mL and 2 µg/mL, respectively) were higher than the MIC90 of all the other anti-pseudomonal beta-lactams (APBLs). Only 1 VGS strain had a penicillin MIC ≥ 2 µg/mL by the Etest (3.6 %). There were no cases with acute respiratory distress syndrome (ARDS) that was associated with VSB, although the rate of viridans group streptococcal shock syndrome was high (26 %). The crude 30-day mortality rate in the VSB group (10.7 %) did not differ significantly from that in the BSI without VSB group (9.3 %) or non-BSI group (7.0 %) (P = 0.77). Also, VSB was not a risk factor for all-cause mortality up to 60 days following allo-HSCT (P = 0.43). CONCLUSIONS: APBL with increased anti-VGS activity (APBL-VA) monotherapy would typically be optimal for treating the VGS strains in this setting. Indication of adding an empiric anti-gram-positive agent to APBL-VA for treating VSB should depend on local factors, such as the susceptibility results. In addition, breakthrough VSB is probably not a major cause of death in allo-HSCT settings, where beta-lactam non-susceptible VGS and the ARDS are rare.

[Harmonization of TSH Measurements.]

The measured concentration of thyroid stimulating hormone (TSH) differs depending on the reagents used. Harmonization of TSH is crucial because the decision limits are described in current clinical practice guide- lines as absolute values, e.g. 2.5 mIU/L in early pregnancy. In this study, we tried to harmonize the report- ed concentrations of TSH using the all-procedure trimmed mean. TSH was measured in 146 serum samples, with values ranging from 0.01 to 18.8 mIU/L, using 4 immunoassays. The concentration of TSH was highest with E test TOSOH and lowest with LUMIPULSE. The concentrations with each reagent were recalculated with the following formulas: E test TOSOH 0.855x-0.014; ECLusys 0.993x+0.079; ARCHITECT 1.041x- 0.010; and LUMIPULSE 1.096x-0.015. Recalculation eliminated the between-assay discrepancy. These formulas may be used until harmonization of TSH is achieved by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC).

A novel cluster of Mycobacterium abscessus complex revealed by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS).

Mycobacterium abscessus complex is a rapidly growing mycobacterium consisting of 3 subspecies, M. abscessus, Mycobacterium massiliense, and Mycobacterium bolletii. However, rapid and accurate species identification is difficult. We first evaluated a suitable protocol of matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) for distinguishing these subspecies. Then, we studied spectral signals by MALDI-TOF MS in 59 M. abscessus, 42 M. massiliense, and 2 M. bolletii. Among several specific spectral signals, 4 signals clearly differentiate M. massiliense from the other 2 subspecies, M. abscessus and M. bolletii. Moreover, 6 of the 42 M. massiliense isolates showed a spectral pattern similar to M. abscessus. These isolates correspond to the distinctive class of M. massiliense (cluster D) which is closer to M. abscessus by the previous variable number tandem repeat analysis. These results indicate that MALDI-TOF MS is not only useful for the identification of 3 subspecies of M. abscessus complex but also capable of distinguishing clusters of M. massiliense.

Familial hypocalciuric hypercalcemia with a de novo heterozygous mutation of calcium-sensing receptor.

UNLABELLED: A de novo heterozygous inactivating mutation of calcium-sensing receptor (CASR) gene typically causes neonatal hyperparathyroidism (NHPT) with moderate hypercalcemia and hyperparathyroid bone disease. We present a case of asymptomatic hypocalciuric hypercalcemia with a de novo heterozygous mutation in CASR, S591C, which is primarily reported to be responsible for NHPT. A 54-year-old female was referred for investigation of asymptomatic hypercalcemia that was initially found in the 1980s but without a history of bone disease during the perinatal period. She had moderate hypercalcemia (12.4 mg/dl) and relative hypocalciuria (fractional extraction of calcium 1.07%) but normal intact parathyroid hormone and serum 1,25-dihydroxyvitamin D3. Pedigree analysis revealed that she carried a de novo heterozygous mutation of S591C, which she transmitted to an affected child with moderate hypercalcemia but not to other children, who had normal serum calcium levels. A de novo heterozygous CASR mutation that is responsible for NHPT may also present in individuals with asymptomatic hypocalciuric hypercalcemia. Caution is required when predicting course and outcome in a pedigree with CASR mutation, as well as incidental hypercalcemia, because of its variable phenotypes. LEARNING POINTS: The phenotype and severity of CASR mutations are thought to be dependent on genotypes.We report an asymptomatic case of the de novo heterozygous S591C mutation in CASR, which has previously been reported as a responsible mutation of NHPT with bone diseases.Variable phenotypes of CASR raise a cautionary note about predicting outcome by genotyping in a pedigree with CASR mutation.