Recent advances in autosomal-dominant polycystic kidney disease.

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease in adults, affecting one in every 1000 Australians. It is caused by loss-of-function heterozygous mutations in either PKD1 or PKD2 , which encode the proteins, polycystin-1 and polycystin-2 respectively. The disease hallmark is the development of hundreds of microscopic fluid-filled cysts in the kidney during early childhood, which grow exponentially and continuously through life at varying rates (between 2% and 10% per year), causing loss of normal renal tissue and up to a 50% lifetime risk of dialysis-dependent kidney failure. Other systemic complications include hypertensive cardiac disease, hepatic cysts, intracranial aneurysms, diverticular disease and hernias. Over the last two decades, advances in the genetics and pathogenesis of this disease have led to novel treatments that reduce the rate of renal cyst growth and may potentially delay the onset of kidney failure. New evidence indicates that conventional therapies (such as angiotensin inhibitors and statins) have mild attenuating effects on renal cyst growth and that systemic levels of vasopressin are critical for promoting renal cyst growth in the postnatal period. Identifying and integrating patient-centred perspectives in clinical trials is also being advocated. This review will provide an update on recent advances in the clinical management of ADPKD.

Update on transcobalamin deficiency: clinical presentation, treatment and outcome.

Transcobalamin (TC) transports cobalamin from blood into cells. TC deficiency is a rare autosomal recessive disorder usually presenting in early infancy with failure to thrive, weakness, diarrhoea, pallor, anemia, and pancytopenia or agammaglobulinemia. It can sometimes resemble neonatal leukemia or severe combined immunodeficiency disease. Diagnosis of TC deficiency is suspected based on megaloblastic anemia, elevation of total plasma homocysteine, and blood or urine methylmalonic acid. It is confirmed by studying the synthesis of TC in cultured fibroblasts, or by molecular analysis of the TCN2 gene. TC deficiency is treatable with supplemental cobalamin, but the optimal type, route and frequency of cobalamin administration and long term patient outcomes are unknown. Here we present a series of 30 patients with TC deficiency, including an update on multiple previously published patients, in order to evaluate the different treatment strategies and provide information about long term outcome. Based on the data presented, current practice appears to favour treatment of individuals with TC deficiency by intramuscular injections of hydroxy- or cyanocobalamin. In most cases presented, at least weekly injections (1 mg IM) were necessary to ensure optimal treatment. Most centres adjusted the treatment regimen based on monitoring CBC, total plasma homocysteine, plasma and urine methylmalonic acid, as well as, clinical status. Finally, continuing IM treatment into adulthood appears to be beneficial.

The Frequencies of Different Inborn Errors of Metabolism in Adult Metabolic Centres: Report from the SSIEM Adult Metabolic Physicians Group.

BACKGROUND: There are few centres which specialise in the care of adults with inborn errors of metabolism (IEM). To anticipate facilities and staffing needed at these centres, it is of interest to know the distribution of the different disorders. METHODS: A survey was distributed through the list-serve of the SSIEM Adult Metabolic Physicians group asking clinicians for number of patients with confirmed diagnoses, types of diagnoses and age at diagnosis. RESULTS: Twenty-four adult centres responded to our survey with information on 6,692 patients. Of those 6,692 patients, 510 were excluded for diagnoses not within the IEM spectrum (e.g. bone dysplasias, hemochromatosis) or for age less than 16 years, leaving 6,182 patients for final analysis. The most common diseases followed by the adult centres were phenylketonuria (20.6%), mitochondrial disorders (14%) and lysosomal storage disorders (Fabry disease (8.8%), Gaucher disease (4.2%)). Amongst the disorders that can present with acute metabolic decompensation, the urea cycle disorders, specifically ornithine transcarbamylase deficiency, were most common (2.2%), followed by glycogen storage disease type I (1.5%) and maple syrup urine disease (1.1%). Patients were frequently diagnosed as adults, particularly those with mitochondrial disease and lysosomal storage disorders. CONCLUSIONS: A wide spectrum of IEM are followed at adult centres. Specific knowledge of these disorders is needed to provide optimal care including up-to-date knowledge of treatments and ability to manage acute decompensation.

Asn(78) and His(81) form a destabilizing locus within the Max HLH-LZ homodimer.

The human Max protein lies at the center of the Myc/Max/Mad family of transcription factors. Its role at the center of this regulatory network is dependent on the helix-loop-helix leucine zipper (HLH-LZ) dimerization domain. The Max LZ contains three residues that deviate from the pattern of hydrophobic amino acids normally present at the interface of LZ dimers: Asn(78), His(81) and Asn(92). In contrast to interfacial Asn residues in other LZ proteins, we have shown that Asn(92) does not act to destabilize the homodimer. Here we describe thermal denaturation experiments performed on Asn(78) and His(81) mutants demonstrating that these residues are involved in actively destabilizing the Max homodimer.

The mild form of menkes disease: a 34 year progress report on the original case.

Classical Menkes disease is a neurodegenerative disorder caused by mutations in the copper-transporting ATPase ATP7A gene which, when untreated, is usually fatal in early childhood. A mild form of Menkes disease was originally reported in 1981 and clinical progress of the patient at 10 years described subsequently. The causative mutation is c.4085C>T in exon 21, causing an alanine to valine substitution in the highly conserved TM7 domain at the C-terminal end of the Menkes protein. Here we report his status at 34 years of age. Intellectual impairment is mild. Ataxia has nearly resolved but motor retardation, dysarthria and an extreme slow speech rate remain. In contrast to patients with the occipital horn syndrome, there have been no connective tissue complications of his mild Menkes disease. He has been under long-term copper therapy for more than 30 years and he continues to enjoy a good quality of life.

Homocysteine and erythrocyte sedimentation rate correlate with cerebrovascular disease in fabry disease.

BACKGROUND: Cerebrovascular disease (CVD) is a common clinical problem in Fabry disease; however, expression of this disease manifestation is not uniform and risk factors for its development are not well studied. A number of common CVD risk factors are known in the general population, and these may also play a role in the development of CVD in Fabry disease. AIM: To evaluate the potential associations between various risk factors and CVD in patients with Fabry disease. METHODS AND RESULTS: Thirty-two Fabry disease patients were studied, with 15 having evidence of CVD. T-tests were used to compare the positive and negative CVD groups and logistic regression was used to look for correlations with CVD history. CVD-positive patients were older (49.73 vs. 37.59 years, p<0.001) and had worse renal function (GFR 61.53 vs. 96.61 mL/min/1.73 m(2), p < 0.005), higher homocysteine (17.79 vs. 10.53 µmol/L, p < 0.05) and erythrocyte sedimentation rate (ESR) levels (23.8 vs. 7.64 mm/h, p < 0.001), and elevated Mainz Severity Score Index (MSSI) scores (23.8 vs. 11.8, p < 0.001). Correlations were found between age (odds ratio (OR) 1.11), DTPA glomerular filtration rate (OR 0.95), homocysteine concentration (OR 1.22), ESR (OR 1.16) and the MSSI (OR 1.19) scores with a positive CVD history (all p < 0.05). CONCLUSION: Elevated homocysteine and ESR are independent risk factors for CVD in Fabry disease. This finding adds to our ability to predict those patients with Fabry disease who are at a higher risk of developing CVD, and may be an aid in deciding which patients should have primary CVD prevention therapies.

Interfacial asparagine residues within an amide tetrad contribute to Max helix-loop-helix leucine zipper homodimer stability.

The transcription factor Max is the obligate dimerization partner of the Myc oncoprotein. The pivotal role of Max within the Myc regulatory network is dependent upon its ability to dimerize via the helix-loop-helix leucine zipper domain. The Max homodimer contains a tetrad of polar residues at the interface of the leucine zipper domain. A conserved interfacial Asn residue at an equivalent position in two other leucine zipper proteins has been shown to decrease homodimer stability. The unusual arrangement of this Gln-Asn/Gln'-Asn' tetrad prompted us to investigate whether Asn(92) plays a similar role in destabilizing the Max homodimer. This residue was sequentially replaced with aliphatic and charged residues. Thermal denaturation, redox time course and analytical ultracentrifugation studies show that the N92V mutation does not increase homodimer stability. Replacing this residue with negatively charged side chains in N92D and N92E destabilizes the mutant homodimer. Further replacement of Gln(91) indicated that H bonding between Gln(91) and Asn(92) residues is not significant to the stability of the native protein. These data collectively demonstrate the central role of Asn(92) in homodimer interactions. Molecular modelling studies illustrate the favorable packing of the native Asn residue at the dimer interface compared with that of the mutant Max peptides.