Management of a Preterm Infant with Renal Tubular Dysgenesis: A Case Report and Review of the Literature.

Renal tubular dysgenesis (RTD) is the absence or poor development of the renal proximal tubules caused by gene mutations in the renin-angiotensin system. Although RTD has been considered fatal, improving neonatal intensive care management has enhanced survival outcomes. However, little has been reported on the survival of extremely preterm infants. This study reports the survival of an extremely preterm infant with RTD and discusses the appropriate management of RTD by reviewing the literature. A female infant weighing 953 g was delivered at 27 weeks' gestation by Cesarean section because of oligohydramnios. She exhibited severe persistent pulmonary hypertension, severe systemic hypotension, and renal dysfunction shortly after birth. Respiratory management was successfully undertaken using nitric oxide inhalation and high-frequency oscillatory ventilation. Desmopressin was effective in maintaining her blood pressure and urinary output. She was diagnosed with RTD based on genetic testing, which revealed a compound heterozygous mutation in the angiotensin-converting enzyme gene in exon 18 (c.2689delC; p.Pro897fs) and exon 20 (c.3095dupT; p.Leu1032fs). At 2 years, she started receiving oral fludrocortisone for treating persistently high serum creatinine levels, which was attributed to nephrogenic diabetes insipidus caused by RTD. Subsequently, her urine output decreased, and renal function was successfully maintained. Currently, there is no established treatment for RTD. Considering cases reported to date, treatment with vasopressin and fludrocortisone appears to be most effective for survival and maintenance of renal function in patients with RTD. This study presents the successful management of RTD using this strategy in an extremely preterm infant.

Salt supplementation ameliorates developmental kidney defects in COX-2-/- mice.

Deficiency of cyclooxygenase-2 (COX-2) activity in the early postnatal period causes impairment of kidney development leading to kidney insufficiency. We hypothesize that impaired NaCl reabsorption during the first days of life is a substantial cause for nephrogenic defects observed in COX-2-/- mice and that salt supplementation corrects these defects. Daily injections of NaCl (0.8 mg·g-1·day-1) for the first 10 days after birth ameliorated impaired kidney development in COX-2-/- pups resulting in an increase in glomerular size and fewer immature superficial glomeruli. However, impaired renal subcortical growth was not corrected. Increasing renal tubular flow by volume load or injections of KCl did not relieve the renal histomorphological damage. Administration of torsemide and spironolactone also affected nephrogenesis resulting in diminished glomeruli and cortical thinning. Treatment of COX-2-/- pups with NaCl/DOCA caused a stronger mitigation of glomerular size and induced a slight but significant growth of cortical tissue mass. After birth, renal mRNA expression of NHE3, NKCC2, ROMK, NCCT, ENaC, and Na+/K+-ATPase increased relative to postnatal day 2 in wild-type mice. However, in COX-2-/- mice, a significantly lower expression was observed for NCCT, whereas NaCl/DOCA treatment significantly increased NHE3 and ROMK expression. Long-term effects of postnatal NaCl/DOCA injections indicate improved kidney function with normalization of pathologically enhanced creatinine and urea plasma levels; also, albumin excretion was observed. In summary, we present evidence that salt supplementation during the COX-2-dependent time frame of nephrogenesis partly reverses renal morphological defects in COX-2-/- mice and improves kidney function.

ACE serum level and I/D gene polymorphism in children with obstructive uropathies and other congenital anomalies of the kidney and urinary tract.

AIM: The aim of this study was to investigate the association of an insertion/deletion (I/D) polymorphism in angiotensin-converting enzyme (ACE) gene with serum ACE level in relation to the type and severity of malformations from congenital anomalies of the kidney and urinary tract (CAKUT) spectrum. METHODS: A group of 134 Bulgarian children with CAKUT divided into four subgroups according to the leading malformation and 109 controls were genotyped by classical polymerase chain reaction. The quantitative determination of serum ACE was performed by ELISA method. RESULTS: A significant elevation of DD-genotype was observed in high-grade hydronephrosis compared to low-grade (43% vs. 9%). The carrying of DD-genotype was associated with higher risk for severe hydronephrosis with OR = 7.5 (95% CI: 1.242÷45.278; P = 0.028). Also, elevated serum ACE concentrations in patients with high-grade compared to low-grade hydronephrosis (237.4 ± 45 ng/mL vs 180.5 ± 64 ng/mL; P = 0.0065) were found. ACE level was significantly lower in patients with unilateral renal agenesis; hypo/dysplasia and multicystic dysplastic kidney (156.6 ± 54 ng/mL) than controls (200.6 ± 56.7 ng/mL; P = 0.005) and the remaining CAKUT subgroups. CONCLUSION: The DD genotype of I/D ACE polymorphism encodes the highest serum ACE level may be an additional genetic risk factor contributing to the severe hydronephrosis in Bulgarian patients with obstructive uropathies in contrast to other investigated categories of CAKUT malformations.

STAR syndrome-associated CDK10/Cyclin M regulates actin network architecture and ciliogenesis.

CDK10/CycM is a protein kinase deficient in STAR (toe Syndactyly, Telecanthus and Anogenital and Renal malformations) syndrome, which results from mutations in the X-linked FAM58A gene encoding Cyclin M. The biological functions of CDK10/CycM and etiology of STAR syndrome are poorly understood. Here, we report that deficiency of CDK10/Cyclin M promotes assembly and elongation of primary cilia. We establish that this reflects a key role for CDK10/Cyclin M in regulation of actin network organization, which is known to govern ciliogenesis. In an unbiased screen, we identified the RhoA-associated kinase PKN2 as a CDK10/CycM phosphorylation substrate. We establish that PKN2 is a bone fide regulator of ciliogenesis, acting in a similar manner to CDK10/CycM. We discovered that CDK10/Cyclin M binds and phosphorylates PKN2 on threonines 121 and 124, within PKN2's core RhoA-binding domain. Furthermore, we demonstrate that deficiencies in CDK10/CycM or PKN2, or expression of a non-phosphorylatable version of PKN2, destabilize both the RhoA protein and the actin network architecture. Importantly, we established that ectopic expression of RhoA is sufficient to override the induction of ciliogenesis resulting from CDK10/CycM knockdown, indicating that RhoA regulation is critical for CDK10/CycM's negative effect on ciliogenesis. Finally, we show that kidney sections from a STAR patient display dilated renal tubules and abnormal, elongated cilia. Altogether, these results reveal CDK10/CycM as a key regulator of actin dynamics and a suppressor of ciliogenesis through phosphorylation of PKN2 and promotion of RhoA signaling. Moreover, they suggest that STAR syndrome is a ciliopathy.

The KAT6B-related disorders genitopatellar syndrome and Ohdo/SBBYS syndrome have distinct clinical features reflecting distinct molecular mechanisms.

Genitopatellar syndrome (GPS) and Say-Barber-Biesecker-Young-Simpson syndrome (SBBYSS or Ohdo syndrome) have both recently been shown to be caused by distinct mutations in the histone acetyltransferase KAT6B (a.k.a. MYST4/MORF). All variants are de novo dominant mutations that lead to protein truncation. Mutations leading to GPS occur in the proximal portion of the last exon and lead to the expression of a protein without a C-terminal domain. Mutations leading to SBBYSS occur either throughout the gene, leading to nonsense-mediated decay, or more distally in the last exon. Features present only in GPS are contractures, anomalies of the spine, ribs and pelvis, renal cysts, hydronephrosis, and agenesis of the corpus callosum. Features present only in SBBYSS include long thumbs and long great toes and lacrimal duct abnormalities. Several features occur in both, such as intellectual disability, congenital heart defects, and genital and patellar anomalies. We propose that haploinsufficiency or loss of a function mediated by the C-terminal domain causes the common features, whereas gain-of-function activities would explain the features unique to GPS. Further molecular studies and the compilation of mutations in a database for genotype-phenotype correlations (www.LOVD.nl/KAT6B) might help tease out answers to these questions and understand the developmental programs dysregulated by the different truncations.

Mutations in KAT6B, encoding a histone acetyltransferase, cause Genitopatellar syndrome.

Genitopatellar syndrome (GPS) is a skeletal dysplasia with cerebral and genital anomalies for which the molecular basis has not yet been determined. By exome sequencing, we found de novo heterozygous truncating mutations in KAT6B (lysine acetyltransferase 6B, formerly known as MYST4 and MORF) in three subjects; then by Sanger sequencing of KAT6B, we found similar mutations in three additional subjects. The mutant transcripts do not undergo nonsense-mediated decay in cells from subjects with GPS. In addition, human pathological analyses and mouse expression studies point to systemic roles of KAT6B in controlling organismal growth and development. Myst4 (the mouse orthologous gene) is expressed in mouse tissues corresponding to those affected by GPS. Phenotypic differences and similarities between GPS, the Say-Barber-Biesecker variant of Ohdo syndrome (caused by different mutations of KAT6B), and Rubinstein-Taybi syndrome (caused by mutations in other histone acetyltransferases) are discussed. Together, the data support an epigenetic dysregulation of the limb, brain, and genital developmental programs.

De novo mutations of the gene encoding the histone acetyltransferase KAT6B cause Genitopatellar syndrome.

Genitopatellar syndrome (GPS) is a rare disorder in which patellar aplasia or hypoplasia is associated with external genital anomalies and severe intellectual disability. Using an exome-sequencing approach, we identified de novo mutations of KAT6B in five individuals with GPS; a single nonsense variant and three frameshift indels, including a 4 bp deletion observed in two cases. All identified mutations are located within the terminal exon of the gene and are predicted to generate a truncated protein product lacking evolutionarily conserved domains. KAT6B encodes a member of the MYST family of histone acetyltranferases. We demonstrate a reduced level of both histone H3 and H4 acetylation in patient-derived cells suggesting that dysregulation of histone acetylation is a direct functional consequence of GPS alleles. These findings define the genetic basis of GPS and illustrate the complex role of the regulation of histone acetylation during development.

Impaired proteostasis contributes to renal tubular dysgenesis.

Protein conformational disorders are associated with the appearance, persistence, accumulation, and misprocessing of aberrant proteins in the cell. The etiology of renal tubular dysgenesis (RTD) is linked to mutations in the angiotensin-converting enzyme (ACE). Here, we report the identification of a novel ACE mutation (Q1069R) in an RTD patient. ACE Q1069R is found sequestered in the endoplasmic reticulum and is also subject to increased proteasomal degradation, preventing its transport to the cell surface and extracellular fluids. Modulation of cellular proteostasis by temperature shift causes an extension in the processing time and trafficking of ACE Q1069R resulting in partial rescue of the protein processing defect and an increase in plasma membrane levels. In addition, we found that temperature shifting causes the ACE Q1069R protein to be secreted in an active state, suggesting that the mutation does not affect the enzyme's catalytic properties.

Inherited renal tubular dysgenesis may not be universally fatal.

Inherited renal tubular dysgenesis (RTD) is caused by mutations in the genes encoding components of the renin-angiotensin cascade: angiotensinogen, renin, angiotensin-converting enzyme (ACE), and angiotensin ΙΙ receptor type 1. It is characterized by oligohydramnios, prematurity, hypotension, hypocalvaria, and neonatal renal failure. The histological hallmark is the absence or poor development of renal proximal tubules. Except for a few cases, the prognosis has been thought to be universally poor, with patients dying either in utero or shortly after birth. We report a 3-year-old infant diagnosed clinically with RTD. The infant survived the neonatal period after 2 weeks of anuria subsequently subsiding. Hypotension and hyperkalemia normalized eventually with administration of fludrocortisone. A revision of renal tissue obtained from a sibling that died shortly after birth revealed normal glomeruli and distal tubules but no identifiable proximal tubules. A novel mutation in the ACE gene was found in the surviving child, who remains with stage 4 chronic kidney disease and normal neurodevelopment. As the number of surviving cases of RTD increases, it should be emphasized to the parents and the neonatal care team that it may not be universally fatal as previously reported. A trial of fludrocortisone may correct hyperkalemia and hypotension.

Anorectal and urinary anomalies and aberrant retinoic acid metabolism in cytochrome P450 oxidoreductase deficiency.

CONTEXT: Cytochrome P450 oxidoreductase (POR) is an electron donor for all microsomal P450 enzymes including CYP26 involved in inactivation of all-trans retinoic acid (atRA). Although previous studies in Por knockout mice suggest that atRA accumulation is relevant to various posterior organ abnormalities, a systematic analysis has not been performed for anorectal and urinary anomalies in patients with POR deficiency (PORD). OBJECTIVE: To report the frequencies of anorectal and urinary anomalies and plasma atRA values in PORD patients. PATIENTS: We studied 37 Japanese patients with PORD, consisting of 15 homozygotes for R457H (group A), 15 compound heterozygotes for R457H and one apparently null mutation (group B), and seven patients with other combinations of mutations (group C). Since R457H is a severe hypomorphic mutation, the residual POR function is predicted to be higher in group A than in group B. RESULTS: Imperforate anus was observed in four patients (10.8%) and vesicoureteral reflux was found in three patients (8.1%), with no significant difference in the frequencies of such anomalies between groups A and B. In addition, a complex urogenital malformation including penile agenesis was identified in one patient. Plasma atRA values were above the reference range in nine of 12 patients examined, and were similar between groups A and B and between patients with and without anomalies. CONCLUSIONS: The results imply that aberrant atRA metabolism due to CYP26 deficiency underlies various anorectal and urinary anomalies in patients with PORD. Clinical phenotypes may be primarily determined by maternal oral retinol intake during pregnancy, and plasma atRA values may be largely influenced by the amount of postnatal oral retinol intake in such patients.

Beta-ureidopropionase deficiency presenting with congenital anomalies of the urogenital and colorectal systems.

Beta-ureidopropionase deficiency (McKusick 606673) is an autosomal recessive condition caused by mutations in the UPB1 gene. To date, five patients have been reported, including one putative case detected through newborn screening. Clinical presentation includes neurological and developmental problems. Here, we report another case of beta-ureidopropionase deficiency who presented with congenital anomalies of the urogenital and colorectal systems and with normal neurodevelopmental milestones. Analysis of a urine sample, because of the suspicion of renal stones on ultrasound, showed strongly elevated levels of the characteristic metabolites, N-carbamyl-beta-amino acids. Subsequent analysis of UPB1 identified a novel mutation 209 G>C (R70P) in exon 2 and a previously reported splice receptor mutation IVS1-2A>G. Expression studies of the R70P mutant enzyme showed that the mutant enzyme did not possess any residual activity. Long-term follow-up is required to determine the clinical significance of the beta-ureidopropionase deficiency in our patient.

Mutations in PHD-like domain of the ATRX gene correlate with severe psychomotor impairment and severe urogenital abnormalities in patients with ATRX syndrome.

Mutations in ATRX are associated with a wide and clinically heterogeneous spectrum of X-linked mental retardation syndromes. The ATRX protein, involved in chromatin remodelling, belongs to the family of SWI/SNF DNA helicases and contains a plant homeodomain (PHD)-like domain. To date, more than 60 different mutations have been reported in ATRX. One of them is recurrent and accounts for 20% of all the reported mutations, whereas all others are private. Most mutations are clustered in the two major functional domains, the helicase and the PHD-like domain. So far, no clear genotype-phenotype correlation has been established, with exception to the rare truncating mutations located at the C-terminal part of the protein, which are consistently associated with severe urogenital defects. In this study, we report the molecular analysis performed in 16 families positive for ATRX. Our findings indicate that, in addition to the previously described mutation 'hotspot' in the PHD-like domain, two other protein sections emerge as minor 'hotspots' in the helicase region encoded by exons 18-20 and 26-29, respectively, gathering 33% of all described mutations. Additionally, based on the clinical data collected for 22 patients from the 16 families, we observe that mutations in the PHD-like domain produce severe and permanent psychomotor deficiency, usually preventing patients from walking, as well as constant urogenital abnormalities, while mutations in the helicase domain lead to delayed but correct psychomotor acquisitions together with mild or absent urogenital abnormalities. In summary, mutations in the helicase domain are associated with milder phenotypes than mutations in the PHD-like domain.