Mutations in DSTYK and dominant urinary tract malformations.

BACKGROUND: Congenital abnormalities of the kidney and the urinary tract are the most common cause of pediatric kidney failure. These disorders are highly heterogeneous, and the etiologic factors are poorly understood. METHODS: We performed genomewide linkage analysis and whole-exome sequencing in a family with an autosomal dominant form of congenital abnormalities of the kidney or urinary tract (seven affected family members). We also performed a sequence analysis in 311 unrelated patients, as well as histologic and functional studies. RESULTS: Linkage analysis identified five regions of the genome that were shared among all affected family members. Exome sequencing identified a single, rare, deleterious variant within these linkage intervals, a heterozygous splice-site mutation in the dual serine-threonine and tyrosine protein kinase gene (DSTYK). This variant, which resulted in aberrant splicing of messenger RNA, was present in all affected family members. Additional, independent DSTYK mutations, including nonsense and splice-site mutations, were detected in 7 of 311 unrelated patients. DSTYK is highly expressed in the maturing epithelia of all major organs, localizing to cell membranes. Knockdown in zebrafish resulted in developmental defects in multiple organs, which suggested loss of fibroblast growth factor (FGF) signaling. Consistent with this finding is the observation that DSTYK colocalizes with FGF receptors in the ureteric bud and metanephric mesenchyme. DSTYK knockdown in human embryonic kidney cells inhibited FGF-stimulated phosphorylation of extracellular-signal-regulated kinase (ERK), the principal signal downstream of receptor tyrosine kinases. CONCLUSIONS: We detected independent DSTYK mutations in 2.3% of patients with congenital abnormalities of the kidney or urinary tract, a finding that suggests that DSTYK is a major determinant of human urinary tract development, downstream of FGF signaling. (Funded by the National Institutes of Health and others.).

Copy-number disorders are a common cause of congenital kidney malformations.

We examined the burden of large, rare, copy-number variants (CNVs) in 192 individuals with renal hypodysplasia (RHD) and replicated findings in 330 RHD cases from two independent cohorts. CNV distribution was significantly skewed toward larger gene-disrupting events in RHD cases compared to 4,733 ethnicity-matched controls (p = 4.8 × 10(-11)). This excess was attributable to known and novel (i.e., not present in any database or in the literature) genomic disorders. All together, 55/522 (10.5%) RHD cases harbored 34 distinct known genomic disorders, which were detected in only 0.2% of 13,839 population controls (p = 1.2 × 10(-58)). Another 32 (6.1%) RHD cases harbored large gene-disrupting CNVs that were absent from or extremely rare in the 13,839 population controls, identifying 38 potential novel or rare genomic disorders for this trait. Deletions at the HNF1B locus and the DiGeorge/velocardiofacial locus were most frequent. However, the majority of disorders were detected in a single individual. Genomic disorders were detected in 22.5% of individuals with multiple malformations and 14.5% of individuals with isolated urinary-tract defects; 14 individuals harbored two or more diagnostic or rare CNVs. Strikingly, the majority of the known CNV disorders detected in the RHD cohort have previous associations with developmental delay or neuropsychiatric diseases. Up to 16.6% of individuals with kidney malformations had a molecular diagnosis attributable to a copy-number disorder, suggesting kidney malformations as a sentinel manifestation of pathogenic genomic imbalances. A search for pathogenic CNVs should be considered in this population for the diagnosis of their specific genomic disorders and for the evaluation of the potential for developmental delay.

Poststreptococcal glomerulonephritis in children with congenital anomalies of the kidney and urinary tract.

BACKGROUND: The objective of this study was to assess clinical course and outcome of children with congenital anomalies of the kidney and urinary tract (CAKUT) who had an attack of acute poststreptococcal glomerulonephritis (PSGN). METHOD: Renal status including blood pressure, proteinuria and glomerular filtration rate was retrospectively analyzed in five children with CAKUT and PSGN at the presentation and during the follow up. RESULTS: In the period 2004-2013, 678 patients were diagnosed and recruited in our CAKUT cohort. During this period, 188 patients were hospitalized with the diagnosis of PSGN. A total of five patients had CAKUT and an episode of PSGN (2.6%). Analysis of the follow-up data revealed that three children fully recovered (bilateral vesicoureteral reflux n = 1, ectopic/hypodysplastic kidney n = 1, ureteropelvic junction obstruction n = 1). One child with bilateral hypodysplasia had progressive worsening of the renal function and has been prepared for renal replacement therapy. Another child with single kidney has stable renal function but has significant rising proteinuria, which was not evident on the routine analysis 2 months before the attack of PSGN. CONCLUSION: Poststreptococcal glomerulonephritis in children is generally benign disease with low mortality in acute stage and excellent medium and long-term prognosis. We analyzed our series of PSGN patients and found that 2.6% had anomaly of the urinary tract. The unfavorable outcome was noted in children with single kidney and bilateral renal impairment.

Tricho-rhino-phalangeal syndrome in a 13-year-old girl with chronic renal failure and severe growth retardation.

INTRODUCTION: The tricho-rhino-phalangeal syndrome type III (TRPS III) is a rare autosomal dominantly inherited condition. The main clinical features are sparse and slow-growing hair and nails, a pear-shaped nose with a bulbous tip, elongated and flat philtrum, thin upper lip, cone-shaped epiphyses of the phalanges, and short stature. All patients have a point mutation in the TRPS1 gene. CASE REPORT: In this paper, we present a 13-year-old female with the typical clinical features of TRPS III, extreme growth retardation, severe deformities of both proximal radii resulting in limited extension of the elbows, and chronic renal failure (CRF) in addition. Molecular diagnostics revealed a missense mutation in exon 6 of TRPS1 that she inherited from her father who is also affected with TRPS III, but does not have CRF. In the index patient, the CRF was found to be due to bilateral renal hypodysplasia (RHD). CONCLUSION: Beside the renal dysplasia, the girl had severe deformities of the proximal radii - findings which have not been reported so far in TRPS III.

Clinical and laboratory features of Macedonian children with OCRL mutations.

OCRL mutations, which are a hallmark of Lowe syndrome, have recently been found in patients with isolated renal phenotype (Dent-2 disease). In this report, we describe clinical and laboratory features in five Macedonian children with mutations in the OCRL gene. Children with a clinical diagnosis of Lowe syndrome or Dent disease underwent complete neurological and ophthalmological examination, imaging of the kidney and urinary tract, assessment of renal tubular function, and mutation analysis of the OCRL gene. Two children (18 months and 11 years, respectively) were diagnosed with Lowe syndrome on the basis of congenital cataracts, severe psychomotor retardation, and renal dysfunction. Both children had low molecular weight proteinuria (LMWP) and hypercalciuria, but not Fanconi syndrome. The older one had bilateral nephrolithiasis due to associated hypocitraturia and mild hyperoxaluria. Three children with asymptomatic proteinuria were diagnosed with Dent-2 disease; none had cataracts or neurological deficit. One child showed mild mental retardation. All had LMWP, hypercalciuria, and elevated enzymes (creatine phosphokinase, lactic dehydrogenase). All three children had an abnormal Tc-99m DMSA scan revealing poor visualization of the kidneys with a high radionuclide content in the bladder; none had nephrolithiasis or nephrocalcinosis. In conclusion, children with OCRL mutations may present with very mild phenotype (asymptomatic proteinuria with/without mild mental retardation) or severe classic oculocerebrorenal syndrome of Lowe. Elevated enzymes and abnormal results on the Tc-99m DMSA scan may be useful indicators for Dent-2 disease.

Nephrotic syndrome occurring during tiopronin treatment for cystinuria.

Cystinuria is an autosomal recessive disorder characterized with abnormal tubular reabsorption of cystine and dibasic amino acids leading to cystine urolithiasis. The classical form is caused by mutations in the SLC3A1 gene (OMIM 220100). The cornerstone of the treatment is high hydration and alkalization of the urine to achieve urine pH between 7.0 and 7.5, at which point, cystine solubility in the urine is optimal. These measures very often fail, and thus addition of sulfhydryl agents like penicillamine and tiopronin (mercaptopropionyl glycine) is recommended. Herein, we report a 3-year-old boy with cystinuria resulting in recurrent nephrolithiasis requiring surgery and extracorporeal shock wave lithotripsy. Nine months after introduction of tiopronin, the boy manifested generalized edema, oliguria, and biochemical indices of nephrotic syndrome. Tiopronin was withdrawn, and the boy was given only supportive treatment. Within 10 days, he entered into clinical and biochemical remission. Pediatricians should be aware of this adverse effect of tiopronin, and therefore, testing of the urine with strips or sulfosalicylic acid at least once weekly at home may be very helpful for early detection of proteinuria.

Autoimmune thyroiditis in a child with steroid-dependent nephrotic syndrome.

Autoimmune thyroiditis is rarely described in association with nephrotic syndrome. Herein we report a girl who developed autoimmune thyroiditis insidiously during the course of minimal change nephrotic syndrome. She was steroid-sensitive, but developed severe steroid dependency and did not respond to cyclophosphamide therapy. She went into stable remission with levamisole. Five months after introduction of levamisole a mild goiter was found on systematic examination at school. The diagnosis of autoimmune thyroiditis was established with typical ultrasound appearance of the thyroid gland along with significant titers of antithyroid antibodies. It is very unlikely that levamisole was responsible for thyroiditis because experimental animal administration of high doses of levamisole inhibited lymphocyte infiltration of the thyroid. Since levamisole has had a beneficial effect on the nephrotic syndrome in our patient we decided to continue the treatment. She has been receiving levamisole for 3 years, and no adverse effects have been observed during the treatment period.

Congenital Anomalies of the Kidney and Urinary Tract (CAKUT).

Congenital anomalies of the kidneys and urinary tract (CAKUT) are found in 3-6 out of 1.000 of the newborns, or according to some statistics they are represented in 0.5% of all pregnancies. Congenital abnormalities of the kidneys and urinary tract present a family of diseases of various anatomic spectrum, including renal anomalies, and anomalies of the bladder and urethra. The study was retrospective-prospective which means that it included newly diagnosed patients suffering from CAKUT, as well as those patients with already diagnosed and well defined CAKUT on the basis of imaging studies which have been processed according to the protocol for this study.

Idiopathic hypercalciuria preceding IgA nephritis in a child with recurrent hematuria.

A 5-year-old boy was investigated after an episode of gross hematuria of non-glomerular origin and was found to have idiopathic hypercalciuria. Despite normalization of calciuria he had recurrent attacks of gross hematuria. Since SDS-PAGE analysis of urinary proteins indicated a glomerular origin of hematuria, a renal biopsy was performed and revealed IgA nephropathy. We believe that association of hypercalciuria and IgA nephropathy is by chance, since both are frequently found in children with hematuria. Also, we recommend all children with well-controlled hypercalciuria who experience further attacks of gross hematuria be evaluated for glomerular disease.