Childhood course of renal insufficiency in a family with a uromodulin gene mutation

Mutations in the UMOD gene encoding uromodulin (Tamm-Horsfall glycoprotein) result in the autosomal dominant transmission of progressive renal insufficiency and hypo-uricosuric hyperuricemia leading to gout at an early age. The clinical appearance is characterized by renal insufficiency and gout occurring in the late teenage years, with end-stage kidney disease characteristically developing between 40 and 70 years of age. This report provides a long-term characterization of renal functional decline in three children from one family with a novel UMOD mutation (c.891T>G, p.C297W) who received allopurinol and a low protein diet. While renal functional decline is slow in individuals with UMOD mutations, it may appear early in life and be associated with marked hyperuricemia. Anemia was also noted in this family.     

Renal manifestations of a mutation in the uromodulin (Tamm Horsfall protein) gene

Background:Uromodulin (Tamm Horsfall glycoprotein) is the most abundant protein found in normal human urine. Its function has yet to be determined. Identifying mutations in the uromodulin gene may be helpful in understanding the function of uromodulin. There has been 1 report of 4 families suffering from mutations in the uromodulin gene, resulting in the autosomal dominant transmission of hypouricosuric hyperuricemia and chronic renal failure. This case report describes another family with similar clinical manifestations.Methods:A family was identified with clinical characteristics of hypouricosuric hyperuricemia and renal failure occurring in a mother and daughter. Clinical characteristics were identified, and laboratory studies were obtained in the proband and the proband's daughter. A genetic analysis was performed to evaluate for mutations in the uromodulin gene.Results:The proband suffered from hyperuricemia at an early age and progressive renal failure with end-stage renal disease developing at age 49 years. The proband's daughter suffered from hyperuricemia, a reduced fractional excretion of uric acid, and mild renal insufficiency. A g.2105G > A mutation in exon 4 of the uromodulin gene resulting in a substitution of tyrosine for cysteine was identified in both the proband and the proband's daughter. The clinical characteristics were similar to those of other patients suffering from uromodulin mutations and to those of patients suffering from medullary cystic kidney disease type 2 and familial juvenile hyperuricemic nephropathy.Conclusion:Uromodulin associated kidney disease results in hyperuricemia and renal failure. The specific uromodulin mutation found in this family is consistent with the hypothesis that mutations disrupt highly conserved cysteine residues in the uromodulin protein. Potential mechanisms for these pathologic changes are discussed. The authors would appreciate referral of other families for screening for mutations.     

Mutations in the uromodulin gene decrease urinary excretion of Tamm-Horsfall protein

BACKGROUND: Mutations in the uromodulin (UMOD) gene that encodes Tamm-Horsfall protein (THP) cause an autosomal-dominant form of chronic renal failure. We have now investigated effects of UMOD gene mutations on protein expression by quantitatively measuring THP excretion. METHODS: THP excretion was determined by enzyme-linked immunosorbent assay (ELISA) of urine collections obtained from 16 related individuals with a 27 bp deletion in the UMOD gene and seven individuals with other UMOD mutations. THP excretion of 22 control subjects (18 genetically related individuals and four spouses in the UMOD deletion family) was also determined. RESULTS: The 16 individuals carrying the deletion mutation excreted 5.8 +/- 6.3 mg THP/g creatinine into their urine. The 18 unaffected relatives from the same family excreted 40.8 +/- 9.7 mg THP/g creatinine (P < 0.0001) and the four spouses excreted 43.9 +/- 25.1 mg THP/g creatinine (P < 0.0001 vs. individuals with the deletion mutation). THP excretion of seven individuals with other UMOD gene mutations was also extremely low (range of 0.14 to 5.9 mg THP/g creatinine). All individuals with UMOD mutations had low THP excretion, irrespective of gender, glomerular filtration rate (GFR), or age. CONCLUSION: These studies quantitatively show that the autosomal-dominant gene mutations responsible for UMOD-associated kidney disease cause a profound reduction of THP excretion. We speculate that this suppression of normal THP excretion reflects deleterious effects of mutated THP within the kidney. Such effects may also play an important role in the pathogenesis of the progressive renal failure observed in patients with UMOD gene mutations.     

Functional consequences of a novel uromodulin mutation in a family with familial juvenile hyperuricaemic nephropathy

Background. Familial juvenile hyperuricaemic nephropathy (FJHN)is an autosomal-dominant disorder featuring hyperuricaemia,low fractional urate excretion, interstitial nephritis and chronicrenal failure. The responsible gene UMOD was recently identified.UMOD encodes for uromodulin or Tamm–Horsfall glycoprotein,the most abundant protein in normal urine. We encountered afamily with FJHN and identified a novel UMOD mutation in exon6. Methods. We sequenced the gene in all family members, identifiedthe mutation, and verified its presence in the affected members.We next performed functional studies of the mutant protein byimmunofluorescence and FACS analysis on transfected cells. Results. The mutation p.C347G (c.1039T>G) results in a conservedcysteine to glycine amino acid substitution in the uromodulinzona pellucida (ZP) domain. The cell studies showed that thenovel uromodulin mutation causes a delay in protein export tothe plasma membrane due to its retention in the endoplasmicreticulum. Conclusions. We describe the first reported mutation mappingin the ZP uromodulin domain. Our data provide further evidenceshowing why the excretion of uromodulin is reduced in this syndrome.     

The rediscovery of uromodulin (Tamm-Horsfall protein): from tubulointerstitial nephropathy to chronic kidney disease

Uromodulin (Tamm-Horsfall protein) is the most abundant protein excreted in the urine under physiological conditions. It is exclusively produced in the kidney and secreted into the urine via proteolytic cleavage. Its biological function is still not fully understood. Uromodulin has been linked to water/electrolyte balance and to kidney innate immunity. Also, studies in knockout mice demonstrated that it has a protective role against urinary tract infections and renal stone formation. Mutations in the gene encoding uromodulin lead to rare autosomal dominant diseases, collectively referred to as uromodulin-associated kidney diseases. They are characterized by progressive tubulointerstitial damage, impaired urinary concentrating ability, hyperuricemia, renal cysts, and progressive renal failure. Novel in vivo studies point at intracellular accumulation of mutant uromodulin as a key primary event in the disease pathogenesis. Recently, genome-wide association studies identified uromodulin as a risk factor for chronic kidney disease (CKD) and hypertension, and suggested that the level of uromodulin in the urine could represent a useful biomarker for the development of CKD. In this review, we summarize these recent investigations, ranging from invalidation studies in mouse to Mendelian disorders and genome-wide associations, which led to a rediscovery of uromodulin and boosted the scientific and clinical interest for this long discovered molecule.     

Isoelectric focusing of native urinary uromodulin (Tamm-Horsfall protein) shows no physicochemical differences between stone formers and non-stone formers

Recent studies have suggested the occurrence of an abnormal form of uromodulin in stone formers which may be related to a reduced sialic acid content of the protein in these patients. Previous attempts to demonstrate these differences have required extensive sample processing prior to analysis, which may in itself alter the nature and behaviour of uromodulin. By employing a sensitive detection system of enhanced chemiluminescence on Western blots following isoelectric focusing we have been able to study the physicochemical properties of uromodulin in whole unprocessed urine from 50 idiopathic calcium stone formers and 15 non-stone formers. Uromodulin, desialated in vitro with either acid or neuraminidase was also analysed using the same system. All urine samples analysed from stone formers and non-stone formers showed a single band of pI 3.5 after isoelectric focusing. Desialated uromodulin showed a series of bands ranging from pI 4.0 to 5.1 reflecting different amounts of sialic acid removed. We conclude there are no charge-related differences in native uromodulin between stone formers and non-stone formers, in particular none relating to the sialic acid content of the protein. Received: 5 May 1998 / Accepted: 28 October 1998     

经典型Bartter综合征家系CLCNKB基因突变分析

目的 研究一个经典型Bartter综合征家系CLCNKB基因突变情况。 方法 提取该家系各成员患者外周血淋巴细胞基因组DNA,应用PCR扩增CLCNKB基因全部外显子及侧翼序列,并直接测序检测突变。选取50例无亲缘关系的健康人作为对照。 结果 在患者中检测到1个杂合（错义）突变,其第4号外显子,第482位碱基T→G突变,造成第161位氨基酸由亮氨酸变为精氨酸（482T>G,L161R）;家系中母亲为杂合突变（L161R杂合突变）,父亲未发现突变;查阅国内外文献及人类基因突变数据库,L161R未见报道,属新发现的突变。 结论 发现了一种新的CLCNKB基因突变：L161R。     

Serum Tamm-Horsfall glycoprotein level in children with various renal diseases.

Serum Tamm-Horsfall glycoprotein (THGP) concentrations were measured by a competitive enzyme-linked immunosorbent assay using peroxidase-labeled THGP in 168 patients, aged 10.5 +/- 4.6 years, with various renal diseases. Using this method, THGP was determined in the concentration range of 10-10(3) micrograms/l. Serum THGP levels ranged from 130 to 350 micrograms/l in 32 control subjects, aged 1-16 years with normal renal function. In most patients with renal disease, the serum THGP levels were lower than those in control subjects. In particular, the serum THGP levels were more reduced according to the decrease in the clearance values of endogenous creatinine (CCR). These findings suggested that the measurement of serum THGP levels is helpful in the evaluation of renal function. On the other hand, 3 patients with vesicoureteric reflux showed higher serum THGP levels than control subjects, though the CCR values in 1 of these patients was lower. These high serum THGP levels may be the result of urinary backflow into circulation.     

Possible role of Tamm-Horsfall glycoprotein in calcium oxalate crystallisation

The role of Tamm-Horsfall glycoprotein (THGP) in the crystallisation of calcium oxalate was investigated. The results showed THGP to have a weak inhibitory effect on crystal growth. In contrast, urinary macromolecules showed a strong inhibitory effect. THGP should, therefore, not be considered the main component of urinary macromolecules which have a strong inhibitory effect on crystal growth. However, THGP did enhance crystal production in the early phase of crystallisation. It appears that THGP should be viewed as a promoter rather than an inhibitor of calcium oxalate crystallisation at physiological concentrations.     

Excretion of urinary Tamm-Horsfall glycoprotein in girls with recurrent urinary tract infections

Summary Tamm-Horsfall glycoprotein (THG) might constitute a bacteria-fixing mucus which contributes to the nonimmunological anti-infectious mechanisms of the lower urinary tract. To evaluate the role of THG in girls with idiopathic recurrent lower urinary tract infections, the THG excretion and concentration in 24-h urine were measured by a radial immunodiffusion method in 16 patients with a median age of 9 years and in 14 healthy age-matched girls. The results showed no significant differences in the THG excretion of concentration between the patients and the controls. Transiently decreased THG excretion rates as well as functional changes in the ability and/or capacity to trap bacteria, however, may leave girls periodically prone to colonization of the bladder. Thus, further studies are warranted to evaluate the importance of THG in the bladder defence mechanism.     

Activation of the inflammatory response of neutrophils by Tamm-Horsfall glycoprotein

The activation of human polymorphonuclear leukocytes (PMN) by particulate Tamm-Horsfall glycoprotein (THG) represents an interaction hitherto unrecognized. The potential pathophysiological effect of this phenomenon within the interstitium of the kidney is highlighted by the activation of the respiratory burst, as well as by comprehensive PMN degranulation. Products of the interaction are expressed in terms of phagocytosis, luminol-dependent chemiluminescence, granule marker enzyme release and arachidonic acid metabolism. Significant quantities of the primary, secondary and tertiary granule markers, myeloperoxidase, vitamin B12 binding protein and N-acetyl-beta-D-glucosaminidase, respectively, were secreted in a dose and time-dependent manner. Phagocytosis of the glycoprotein was accompanied by the generation of significant quantities of leukotriene B4. Furthermore, the ability of such a particulate ligand to activate the alternative pathway of complement clearly represents a capacity to augment the inflammatory response. Should the interaction of THG with PMN take place within the interstitium of the kidney, augmented by the deposition of complement proteins on the surface of insoluble aggregates, the resulting inflammatory response may lead to marked tissue damage and eventually result in interstitial fibrosis.     

Clinical and pathologic features of focal segmental glomerulosclerosis with mitochondrial tRNALeu(UUR) gene mutation

BACKGROUND: Several families have been described in which an A to G transition mutation at position 3243 (A3243G) of the mitochondrial DNA (mtDNA) is associated with focal and segmental glomerulosclerosis (FSGS). However, the prevalence, clinical features, and pathophysiology of FSGS carrying mtDNA mutations are largely undefined. METHODS: Among 11 biopsy-proven primary FSGS patients of unknown etiology, we examined seven FSGS patients to determine whether any of the clinical and pathological features of FSGS were associated with an A3243G mtDNA mutation. In four subjects in whom the A3243G mtDNA mutation was discovered in blood leukocytes, as well as in urine sediments, we retrospectively reviewed the medical records and re-evaluated the renal biopsy specimen using light and electron microscopy. We further screened the patient's family members for the presence and degree of heteroplasmy for this mtDNA mutation and obtained medical histories that were consistent with mitochondrial cytopathy. RESULTS: The four individuals identified with the A3243G mtDNA mutation were female. Proteinuria was diagnosed in these individuals during a routine annual health checkup in their teenage years. None of the patients showed any symptoms related to mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode, whereas diabetes mellitus in two of the patients and a hearing disturbance in one patient became manifest within a 3- to 13-year follow-up period. Strict maternal transmitted inheritance was confirmed by pedigree studies in all of these patients. Steroid therapy was ineffective in all four patients. In two of these patients, renal function declined slowly to end-stage renal failure. Histologic examination of biopsy specimens revealed that glomeruli were not hypertrophied, while electron microscopic examination identified severely damaged, multinucleated podocytes containing extremely dysmorphic abnormal mitochondria in all patients. CONCLUSIONS: FSGS may belong to the spectrum of renal involvement in A3243G mtDNA mutation in humans. Severely injured podocytic changes containing abnormal mitochondria may explain the pathogenesis of FSGS in association with the A3243G mtDNA mutation.