Asymmetry indicates more severe and active disease in Graves' orbitopathy: results from a prospective cross-sectional multicentre study.

PURPOSE: Patients with Graves' orbitopathy can present with asymmetric disease. The aim of this study was to identify clinical characteristics that distinguish asymmetric from unilateral and symmetric Graves' orbitopathy. METHODS: This was a multi-centre study of new referrals to 13 European Group on Graves' Orbitopathy (EUGOGO) tertiary centres. New patients presenting over a 4 month period with a diagnosis of Graves' orbitopathy were included. Patient demographics were collected and a clinical examination was performed based on a previously published protocol. Patients were categorized as having asymmetric, symmetric, and unilateral Graves' orbitopathy. The distribution of clinical characteristics among the three groups was documented. RESULTS: The asymmetric group (n = 83), was older than the symmetric (n = 157) group [mean age 50.9 years (SD 13.9) vs 45.8 (SD 13.5), p = 0.019], had a lower female to male ratio than the symmetric and unilateral (n = 29) groups (1.6 vs 5.0 vs 8.7, p < 0.001), had more active disease than the symmetric and unilateral groups [mean linical Activity Score 3.0 (SD 1.6) vs 1.7 (SD 1.7), p < 0.001 vs 1.3 (SD 1.4), p < 0.001] and significantly more severe disease than the symmetric and unilateral groups, as measured by the Total Eye Score [mean 8.8 (SD 6.6) vs 5.3 (SD 4.4), p < 0.001, vs 2.7 (SD 2.1), p < 0.001]. CONCLUSION: Older age, lower female to male ratio, more severe, and more active disease cluster around asymmetric Graves' orbitopathy. Asymmetry appears to be a marker of more severe and more active disease than other presentations. This simple clinical parameter present at first presentation to tertiary centres may be valuable to clinicians who manage such patients.

Expanding the genotypic spectrum of Perrault syndrome.

Perrault syndrome is a rare autosomal recessive disorder characterized by sensorineural hearing loss (SNHL) in both sexes and primary ovarian insufficiency in 46, XX karyotype females. Biallelic variants in five genes are reported to be causative: HSD17B4, HARS2, LARS2, CLPP and C10orf2. Here we present eight families affected by Perrault syndrome. In five families we identified novel or previously reported variants in HSD17B4, LARS2, CLPP and C10orf2. The proband from each family was whole exome sequenced and variants confirmed by Sanger sequencing. A female was compound heterozygous for a known, p.(Gly16Ser) and novel, p.(Val82Phe) variant in D-bifunctional protein (HSD17B4). A family was homozygous for mitochondrial leucyl aminocyl tRNA synthetase (mtLeuRS) (LARS2) p.(Thr522Asn), previously associated with Perrault syndrome. A further family was compound heterozygous for mtLeuRS, p.(Thr522Asn) and a novel variant, p.(Met117Ile). Affected individuals with LARS2 variants had low frequency SNHL, a feature previously described in Perrault syndrome. A female with significant neurological disability was compound heterozygous for p.(Arg323Gln) and p.(Asn399Ser) variants in Twinkle (C10orf2). A male was homozygous for a novel variant in CLPP, p.(Cys144Arg). In three families there were no putative pathogenic variants in these genes confirming additional disease-causing genes remain unidentified. We have expanded the spectrum of disease-causing variants associated with Perrault syndrome.

Serum 25-hydroxyvitamin D concentration and its determinants in the very old: the Newcastle 85+ Study.

SUMMARY: Data on vitamin D status in very old adults are lacking. The aim of this study was to assess 25-hydroxyvitamin D [25(OH)D] concentrations and its predictors in 775 adults aged 85 years old living in North-East England. Low 25(OH)D was alarmingly high during winter/spring months, but its biological significance is unknown. INTRODUCTION: Despite recent concerns about the high prevalence of vitamin D deficiency in much of the British adult and paediatric population, there is a dearth of data on vitamin D status and its predictors in very old adults. The objective of the present study was to describe vitamin D status and its associated factors in a broadly representative sample of very old men and women aged 85 years living in the North East of England (55° N). METHODS: Serum concentrations of 25-hydroxyvitamin D [25(OH)D] were analysed in 775 participants in the baseline phase of the Newcastle 85+ cohort study. Season of blood sampling, dietary, health, lifestyle and anthropometric data were collected and included as potential predictors of vitamin D status in ordinal regression models. RESULTS: Median serum 25(OH)D concentrations were 27, 45, 43 and 33 nmol/L during spring, summer, autumn and winter, respectively. The prevalence of vitamin D deficiency according to North American Institute of Medicine guidelines [serum 25(OH)D <30 nmol/L] varied significantly with season with the highest prevalence observed in spring (51%) and the lowest prevalence observed in autumn (23%; P < 0.001). Reported median (inter-quartile range) dietary intakes of vitamin D were very low at 2.9 (1.2-3.3) µg/day. In multivariate ordinal regression models, non-users of either prescribed or non-prescribed vitamin D preparations and winter and spring blood sampling were associated with lower 25(OH)D concentrations. Dietary vitamin D intake, disability score and disease count were not independently associated with vitamin D status in the cohort. CONCLUSION: There is an alarming high prevalence of vitamin D deficiency (<30 nmol/L) in 85-year-olds living in North East England at all times of the year but particularly during winter and spring. Use of vitamin D containing preparations (both supplements and medications) appeared to be the strongest predictor of 25(OH)D concentrations in these very old adults.

CTLA-4 as a genetic determinant in autoimmune Addison's disease.

In common with several other autoimmune diseases, autoimmune Addison's disease (AAD) is thought to be caused by a combination of deleterious susceptibility polymorphisms in several genes, together with undefined environmental factors and stochastic events. To date, the strongest genomic association with AAD has been with alleles at the HLA locus, DR3-DQ2 and DR4. The contribution of other genetic variants has been inconsistent. We have studied the association of 16 single-nucleotide polymorphisms (SNPs) within the CD28-CTLA-4-ICOS genomic locus, in a cohort comprising 691 AAD patients of Norwegian and UK origin with matched controls. We have also performed a meta-analysis including 1002 patients from European countries. The G-allele of SNP rs231775 in CTLA-4 is associated with AAD in Norwegian patients (odds ratio (OR)=1.35 (confidence interval (CI) 1.10-1.66), P=0.004), but not in UK patients. The same allele is associated with AAD in the total European population (OR=1.37 (CI 1.13-1.66), P=0.002). A three-marker haplotype, comprising PROMOTER_1661, rs231726 and rs1896286 was found to be associated with AAD in the Norwegian cohort only (OR 2.43 (CI 1.68-3.51), P=0.00013). This study points to the CTLA-4 gene as a susceptibility locus for the development of AAD, and refines its mapping within the wider genomic locus.

Rethinking antithyroid drugs in pregnancy.

Uncontrolled hyperthyroidism in pregnancy poses a risk to both mother and foetus, and the optimal treatment strategy in this setting remains elusive. Instigation of pharmacological therapy or an alternative intervention during pregnancy requires careful consideration, and the evidence that has underpinned our choice of antithyroid drug has not been robust. Recent research developments have prompted us to question our practice, and reconsider our approach to managing this patient group.

Role of the X-linked gene GPR174 in autoimmune Addison's disease.

CONTEXT: Autoimmune endocrinopathies demonstrate a profound gender bias, but the reasons for this remain obscure. The 1000 genes on the X chromosome are likely to be implicated in this inherent susceptibility; various theories, including skewed X chromosome inactivation and fetal microchimerism, have been proposed. GPR174 is an Xq21 putative purinergic receptor that is widely expressed in lymphoid tissues. A single-nucleotide polymorphism, rs3827440, encoding Ser162Pro, has recently been associated with Graves' disease in Chinese and Polish populations, suggesting a role of this X chromosome gene in autoimmune disease. OBJECTIVE: We investigated the role of rs3827440 in a UK cohort of patients with autoimmune Addison's disease (AAD). Samples from 286 AAD cases and 288 healthy controls were genotyped using TaqMan single-nucleotide polymorphism genotyping assays (C_25954273_10) on the Applied Biosystems 7900HT Fast real-time PCR system. DESIGN: Using a dominant (present/absent) model, the serine-encoding T allele of rs3827440 was present in 189 of 286 AAD patients (66%) compared with 132 of 288 unaffected controls (46%) [P = .010, odds ratio 1.80 (5%-95% confidence interval 1.22-2.67)]. An allele dosage model found a significant excess of the T allele in AAD patients compared with controls [P = .03, odds ratio 1.34 (5%-95% confidence interval 1.07-1.67)]. CONCLUSION: We have demonstrated a significant association of this X chromosome-encoded immunoreceptor with AAD for the first time. This X-linked gene could have a more generalized role in autoimmunity pathogenesis: G protein-coupled receptors are promising drugable targets, and further work to elucidate the functional role of GPR174 is now warranted.

Consensus statement on the diagnosis, treatment and follow-up of patients with primary adrenal insufficiency.

Primary adrenal insufficiency (PAI), or Addison's disease, is a rare, potentially deadly, but treatable disease. Most cases of PAI are caused by autoimmune destruction of the adrenal cortex. Consequently, patients with PAI are at higher risk of developing other autoimmune diseases. The diagnosis of PAI is often delayed by many months, and most patients present with symptoms of acute adrenal insufficiency. Because PAI is rare, even medical specialists in this therapeutic area rarely manage more than a few patients. Currently, the procedures for diagnosis, treatment and follow-up of this rare disease vary greatly within Europe. The common autoimmune form of PAI is characterized by the presence of 21-hydroxylase autoantibodies; other causes should be sought if no autoantibodies are detected. Acute adrenal crisis is a life-threatening condition that requires immediate treatment. Standard replacement therapy consists of multiple daily doses of hydrocortisone or cortisone acetate combined with fludrocortisone. Annual follow-up by an endocrinologist is recommended with the focus on optimization of replacement therapy and detection of new autoimmune diseases. Patient education to enable self-adjustment of dosages of replacement therapy and crisis prevention is particularly important in this disease. The authors of this document have collaborated within an EU project (Euadrenal) to study the pathogenesis, describe the natural course and improve the treatment for Addison's disease. Based on a synthesis of this research, the available literature, and the views and experiences of the consortium's investigators and key experts, we now attempt to provide a European Expert Consensus Statement for diagnosis, treatment and follow-up.

Isolated Addison's disease is unlikely to be caused by mutations in MC2R, MRAP or STAR, three genes responsible for familial glucocorticoid deficiency.

BACKGROUND: Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease caused by ACTH resistance and leads to isolated glucocorticoid deficiency. Although FGD patients typically have normal mineralocorticoid secretion, subtle alterations in the renin-angiotensin-aldosterone axis have been reported in a subset of patients at presentation. Anecdotally, some patients with FGD have been initially diagnosed as having Addison's disease (AD), with implications for treatment and genetic counselling. Currently, mutations in three genes: the ACTH receptor (MC2R); the melanocortin 2 receptor accessory protein (MRAP); and the steroidogenic acute regulatory protein (STAR) are known to give rise to FGD types 1-3. We investigated a cohort of autoantibody-negative AD patients for mutations in these genes. METHODS: Forty patients with known AD without evidence of autoimmune disease were screened for mutations in MC2R, MRAP and STAR. In addition, patients were genotyped for the MC2R promoter polymorphism previously associated with reduced responsiveness to ACTH. RESULTS: No mutations in MC2R, MRAP or STAR were identified in any patient. The frequencies of the MC2R promoter polymorphism were similar to those reported in healthy controls. CONCLUSIONS: FGD does not appear to be underdiagnosed in the AD population. However, in approximately 50% of patients with FGD, no genetic cause has yet been identified and it is possible that the other, as yet unidentified, genes giving rise to FGD may be implicated in AD.

Impact of standardised reporting in adrenocortical carcinoma: a single centre clinicopathological review.

AIMS: Structured multicentre efforts are needed if the prognosis of adrenocortical carcinoma (ACC) is to be improved. Data collection may be enhanced through standardised histopathological reporting using criteria such as the recently published Royal College of Pathologists' (UK) minimum dataset (MDS). This study aimed to perform a clinicopathological review of the adult patients treated at the Royal Victoria Infirmary, Newcastle upon Tyne, in the 10 years preceding the MDS. METHODS: Case records were examined for all patients diagnosed with ACC between 1996 and 2006. Pathology was reviewed and compared with the Royal College of Pathologists' MDS along with the original reports. A systematic evaluation of Ki-67 immunolabelling was also performed. RESULTS: Eleven patients with ACC were diagnosed and treated. Histopathological reporting according to the MDS identified more features of malignancy than in the original reports (8.5+/-1.2 versus 5.1+/-0.8, p<0.02). The median number of microscopic criteria of malignancy was 7 (range 5-10), with > or =5 features occurring in all cases. The most commonly observed features of malignancy were diffuse architecture, <25% clear cells, confluent necrosis, abnormal mitoses and mitotic count > or =6 per 50 high-power fields. Capsular invasion and > or =8 MDS criteria of malignancy were associated with a worse outcome (each p<0.01). Median Ki-67 index was 19.0% (range 3.7-44.1%) and was not apparently related to survival. CONCLUSIONS: Standardised criteria for histopathological reporting of ACC will improve the accuracy of data for cancer registration and may also assist in individual patient stratification. An elevated Ki-67 index is a feature of ACC, although it does not appear to predict individual patient survival.

The role of the IDDM2 locus in the susceptibility of UK APS1 subjects to type 1 diabetes mellitus.

Autoimmune polyendocrinopathy syndrome type 1 (APS1) is characterized by autoimmune destruction of endocrine tissues and chronic mucocutaneous candidiasis. Type 1 diabetes (T1D) affects 12-25% of patients with APS1, and the prediction of whether this complication will affect an individual is not currently possible. However, alleles of a variable number tandem repeat (VNTR) 5' of the insulin gene are known to influence the development of T1D in the general, non-APS1 population. Therefore, we investigated the prevalence of these IDDM2 alleles in British Caucasian patients with APS1. The study employed genotyping of 33 patients with APS1 for the HphI polymorphism that is in tight linkage disequilibrium with the insulin gene VNTR alleles. Thirty-three patients with APS1 were studied, the mean age was 23.5 years and 24% have T1D. Six of eight (75%) APS1 patients with T1D were homozygous for the class I INS VNTR (susceptibility) allele, compared with eight of 25 (32%) of APS1 patients without T1D (P = 0.042). Our data suggest an association between the development of T1D and homozygosity for the T1D susceptibility class IINS VNTR allele in patients with APS1.

Influences of age, gender, smoking, and family history on autoimmune thyroid disease phenotype.

CONTEXT: Both genetic and environmental factors contribute to susceptibility to Graves' disease (GD) and Hashimoto's thyroiditis (HT), as well as disease manifestations. OBJECTIVE: The objective of the study was to define how endogenous/environmental factors contribute to variation in phenotype. DESIGN/SETTING: This was a multicenter cohort study. PATIENTS/OUTCOME MEASURES: We prospectively collected clinical/biochemical data as part of the protocol for a United Kingdom DNA collection for GD and HT. We investigated, in 2805 Caucasian subjects, whether age at diagnosis, gender, family history (FH), smoking history, and presence of goiter influenced disease manifestations. RESULTS: For 2405 subjects with GD, the presence of goiter was independently associated with disease severity (serum free T4 at diagnosis) (P < 0.001). Free T4 (P < 0.05) and current smoking (P < 0.001) were both independent predictors of the presence of ophthalmopathy. Approximately half of those with GD (47.4% of females, 40.0% of males) and HT (n = 400) (56.4% of females, 51.7% of males) reported a FH of thyroid dysfunction. In GD, a FH of hyperthyroidism in any relative was more frequent than hypothyroidism (30.1 vs. 24.4% in affected females, P < 0.001). In HT, a FH of hypothyroidism was more common than hyperthyroidism (42.1 vs. 22.8% in affected females, P < 0.001). For GD (P < 0.001) and HT (P < 0.05), a FH was more common in maternal than paternal relatives. The reporting of a parent with thyroid dysfunction (hyper or hypo) was associated with lower median age at diagnosis of both GD (mother with hyperthyroidism, P < 0.001) and HT (father with hypothyroidism, P < 0.05). In GD and HT, there was an inverse relationship between the number of relatives with thyroid dysfunction and age at diagnosis (P < 0.01). CONCLUSIONS: Marked associations among age at diagnosis, disease severity, goiter, ophthalmopathy, smoking, and FH provide evidence for interactions between genetic and environmental/endogenous factors; understanding these may allow preventive measures or better tailoring of therapies.

A haplotype of the CYP27B1 promoter is associated with autoimmune Addison's disease but not with Graves' disease in a UK population.

Previous studies have suggested an association between alleles of the CYP27B1 (1-alpha hydroxylase) gene and autoimmune conditions. We have examined three single nucleotide polymorphisms (SNPs) that are located in the 5' region and promoter of the CYP27B1 gene for association in a cohort of Graves' disease and autoimmune Addison's disease subjects from the UK. Genomic DNA samples from white patients with autoimmune Addison's disease (n = 104) and healthy controls (n = 464) were genotyped by PCR-RFLP analysis for the SNPs at positions -1260 and -1077 5' of the coding CYP27B1 sequences. The -1260 SNP was also examined in a cohort of patients with Graves' disease (n = 446). Chi 2 testing of contingency tables was used to determine the significance of genotypes and alleles. Haplotype frequencies and linkage disequilibrium measures were estimated using the UNPHASED and HAPLOVIEW packages. Alleles at the three CYP27B1 markers were in tight linkage disequilibrium with each other and all showed association with autoimmune Addison's disease. The maximum evidence for association was with the -1260 C allele (76.0% in Addison's subjects versus 64.9% in controls; P = 0.003; odds ratio 1.71 (5-95% confidence intervals, 1.20-2.44). A global test of significance for the common -1918 T, -1260 C and -1077 G haplotype was significant in Addison's subjects compared with controls (P = 0.01). In contrast, there was no association of alleles at the -1260 SNP with Graves' disease. We are able to confirm that a CYP27B1 promoter allele is associated with autoimmune Addison's disease, and extend this finding to include an associated promoter haplotype.

The codon 620 tryptophan allele of the lymphoid tyrosine phosphatase (LYP) gene is a major determinant of Graves' disease.

The lymphoid tyrosine phosphatase (LYP), encoded by the protein tyrosine phosphatase-22 (PTPN22) gene, is a powerful inhibitor of T cell activation. Recently, a single nucleotide polymorphism (SNP), encoding a functional arginine to tryptophan residue change at LYP codon 620 has been shown to be associated with type 1 diabetes and other autoimmune disorders. We have used a PCR-restriction fragment (XcmI) assay to examine genotypes at the codon 620 polymorphism in 549 unrelated probands with Graves' disease, 104 unrelated subjects with autoimmune Addison's disease and 429 controls. The T nucleotide at the SNP, encoding the tryptophan 620 residue, was present in 151 of 1098 (13.8%) Graves' disease alleles compared to 67 of 858 (7.8%) control alleles (chi(2) = 17.2, p = 3.4 x 10(-5)' odds ratio = 1.88, 5-95% confidence intervals [CI] 1.39 to 2.55). Similarly, the T nucleotide at the codon 620 SNP was present in 26 of 208 (12.5%) Addison's disease alleles vs 7.8% of controls (chi(2) = 4.63, p = 0.031; odds ratio = 1.69, 5-95% CI 1.04 to 2.73). These data suggest that this LYP polymorphism is a susceptibility allele for Graves' disease with a major effect, and which is likely to have a role in many other autoimmune conditions.

A comparative study of mRNA and protein expression of the autoimmune regulator gene (Aire) in embryonic and adult murine tissues.

Autoimmune polyendocrine syndrome type 1 (APS1) is a rare autosomal recessive human disorder caused by mutations in the autoimmune regulator gene (AIRE) and characterized by multiple autoimmune diseases. As reports of the tissue expression pattern of the murine Aire gene are discordant, a comprehensive survey of Aire expression was undertaken in adult and embryonic tissues at the mRNA and protein levels using real-time RT-PCR, in situ hybridization, and immunohistochemistry. In the adult, the highest Aire mRNA expression was in the thymus. All the other tissues investigated expressed Aire mRNA at low levels, but it was barely detectable in the adrenal gland. Aire protein expression was observed in the thymus, spleen, and lymph nodes. A common pattern was observed in other tissues, with staining in epithelial cells. An exception to this was the gut, where staining was seen in the mucin spaces. In embryonic tissue, Aire mRNA and protein expression was detected from E14.5 in the thymus. In the fetal liver, unlike the adult, staining was observed at E14.5 and decreased towards term. Thus, Aire is expressed in immunologically relevant tissues and in a restricted number of extra-immunological tissues in the adult. Furthermore, the presence of Aire protein is reported in extra-thymic tissues of the embryo.

CTLA4 gene and Graves' disease: association of Graves' disease with the CTLA4 exon 1 and intron 1 polymorphisms, but not with the promoter polymorphism.

OBJECTIVE: Recent studies have shown that Graves' disease (GD) is linked to and associated with alleles of the cytotoxic T lymphocyte antigen-4 (CTLA4) locus. However, the true pathogenic polymorphism(s) at this locus remains uncertain. Moreover, the association studies of the promoter CTLA4(-318)C/T polymorphism in white GD populations have produced conflicting results. Therefore, we have analysed three CTLA4 single nucleotide polymorphisms, including promoter CTLA4(-318)C/T, exon 1 CTLA4(49)A/G and intron 1 CTLA4(1822)C/T in our GD cohort from the UK. PATIENTS AND METHODS: We studied 301 white patients with GD and 349 healthy ethnically matched local controls. Amongst GD probands, 129 had significant thyroid-associated orbitopathy (TAO; NOSPECS class III or worse). The CTLA4(-318)C/T, CTLA4(49)A/G and CTLA4(1822)C/T polymorphisms were genotyped by using the restriction enzymes MseI, Bst71I and HaeIII, respectively. RESULTS: We found no association between GD and alleles of CTLA4(-318)C/T. GD was found to be associated with the G allele of CTLA4(49)A/G[P = 5.9 x 10(-6), odds ratio (OR) 1.65] and the T allele of CTLA4(1822)C/T (P = 7.7 x 10(-6), OR 1.64). The frequencies of these alleles were significantly higher in GD probands with significant TAO than in those without TAO (G allele: P = 0.001, OR 1.68; T allele: P = 0.001, OR 1.70). CONCLUSIONS: The promoter CTLA4(-318)C/T polymorphism is not in linkage disequilibrium with the pathogenic polymorphism(s) at the CTLA4 locus. The alleles of both the exon 1 CTLA4(49)A/G and the intron 1 CTLA4(1822)C/T polymorphisms are associated with GD, which is stronger in patients with TAO.

The investigation of hypocalcaemia and rickets.

Our understanding of disorders that present with hypocalcaemia has advanced rapidly in the past decade. The molecular basis of many of these disorders and conditions associated with phosphate wasting has now been established. While many children will need specialist involvement, they often will present to general paediatricians, and appropriate investigations prior to intervention will enable early diagnosis. Not all children with hypocalcaemia and low or low normal parathyroid hormone levels have isolated hypoparathyroidism, and clinicians need to be aware of the potential for misdiagnosis. Outpatient departments and paediatric wards should have a readily accessible and comprehensive list of bloods that need to be taken when a child presents with hypocalcaemia or rickets.

An association between the CTLA4 exon 1 polymorphism and early rheumatoid arthritis with autoimmune endocrinopathies.

OBJECTIVE: To examine the allelic association of the single nucleotide polymorphism (CTLA4A/G) in exon 1 of the cytotoxic T lymphocyte antigen-4 (CTLA4) gene with early rheumatoid arthritis (RA). METHODS: One hundred and twenty-three unrelated white probands with early RA from the north-east of England and 349 local ethnically matched controls were studied. The CTLA4A/G polymorphism was genotyped with a polymerase chain reaction (PCR) method and digestion with the restriction enzyme Bst71I. Probands were also screened by allele-specific PCR for alleles HLA DRB1*01 and DRB1*04. RESULTS: The frequency of the G allele at CTLA4A/G was significantly increased in probands with early RA compared with controls [43 vs 36%; P=0.028, odds ratio (OR) 1.35, 95% confidence interval (CI) 1.01-1.82]. Most of this increased frequency was attributable to RA individuals with coexisting autoimmune thyroid disease or type 1 diabetes (58 vs 36% in controls; P=0.005, OR 2.50, CI 1.29-4.84). The frequency of the G allele in RA patients without autoimmune endocrinopathy was 40%, which was not significantly different from that in controls (P=0.140). CONCLUSION: The association between the CTLA4 G allele and early RA is largely explained by individuals with RA who have coexisting autoimmune endocrinopathies.

The voltage-dependent Cl(-) channel ClC-5 and plasma membrane Cl(-) conductances of mouse renal collecting duct cells (mIMCD-3).

1. We have tested the hypothesis that the voltage-dependent Cl(-) channel, ClC-5 functions as a plasma membrane Cl(-) conductance in renal inner medullary collecting duct cells. 2. Full-length mouse kidney ClC-5 (mClC-5) was cloned and transiently expressed in CHO-K1 cells. Fast whole-cell patch-clamp recordings confirmed that mClC-5 expression produces a voltage-dependent, strongly outwardly rectifying Cl(-) conductance that was unaffected by external DIDS. 3. Slow whole-cell recordings, using nystatin-perforated patches from transfected CHO-K1 cells, also produced voltage-dependent Cl(-) currents consistent with ClC-5 expression. However, under this recording configuration an endogenous DIDS-sensitive Ca(2+)-activated Cl(-) conductance was also evident, which appeared to be activated by green fluorescent protein (GFP) transfection. 4. A mClC-5-GFP fusion protein was transiently expressed in CHO-K1 cells; confocal laser scanning microscopy (CLSM) showed localization at the plasma membrane, consistent with patch-clamp experiments. 5. Endogenous expression of mClC-5 was demonstrated in mouse renal collecting duct cells (mIMCD-3) by RT-PCR and by immunocytochemistry. 6. Using slow whole-cell current recordings, mIMCD-3 cells displayed three biophysically distinct Cl(-)-selective currents, which were all inhibited by DIDS. However, no cells exhibited whole-cell currents that had mClC-5 characteristics. 7. Transient transfection of mIMCD-3 cells with antisense mClC-5 had no effect on the endogenous Cl(-) conductances. Transient transfection with sense mClC-5 failed to induce the Cl(-) conductance seen in CHO-K1 cells but stimulated levels of the endogenous Ca(2+)-activated Cl(-) conductance 24 h post-transfection. 8. Confocal laser scanning microscopy of mIMCD-3 cells transfected with mClC-5-GFP showed that the protein was absent from the plasma membrane and was instead localized to acidic endosomal compartments. 9. These data discount a major role for ClC-5 as a plasma membrane Cl(-) conductance in mIMCD-3 cells but suggest a role in endosomal function.