Nephrocalcinosis (enamel renal syndrome) caused by autosomal recessive FAM20A mutations

Background/Aims

Calcium homeostasis requires regulated cellular and interstitial systems interacting to modulate the activity and movement of this ion. Disruption of these systems in the kidney results in nephrocalcinosis and nephrolithiasis, important medical problems whose pathogenesis is incompletely understood.

Methods

We investigated 25 patients from 16 families with unexplained nephrocalcinosis and characteristic dental defects (amelogenesis imperfecta, gingival hyperplasia, impaired tooth eruption). To identify the causative gene, we performed genome-wide linkage analysis, exome capture, next-generation sequencing, and Sanger sequencing.

Results

All patients had bi-allelic FAM20A mutations segregating with the disease; 20 different mutations were identified.

Conclusions

This au-tosomal recessive disorder, also known as enamel renal syndrome, of FAM20A causes nephrocalcinosis and amelogenesis imperfecta. We speculate that all individuals with biallelic FAM20A mutations will eventually show nephrocalcinosis.

Kearns-Sayre syndrome presenting as isolated growth failure

Failure to thrive arises from a heterogeneous group of paediatric disorders including defects in energy metabolism such as mitochondrial diseases. Illustrating this, we describe a girl with poor growth who eluded diagnosis until she developed characteristics of Kearns-Sayre syndrome. Her history emphasises that defects of energy metabolism can present as isolated growth failure.

1,25-(OH)2D-24 Hydroxylase (CYP24A1) Deficiency as a Cause of Nephrolithiasis

BACKGROUND AND OBJECTIVES

Elevated serum vitamin D with hypercalciuria can result in nephrocalcinosis and nephrolithiasis. This study evaluated the cause of excess 1,25-dihydroxycholecalciferol (1α,25(OH)2D3) in the development of those disorders in two individuals.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Two patients with elevated vitamin D levels and nephrocalcinosis or nephrolithiasis were investigated at the National Institutes of Health (NIH) Clinical Center and the NIH Undiagnosed Diseases Program, by measuring calcium, phosphate, and vitamin D metabolites, and by performing CYP24A1 mutation analysis.

RESULTS

Both patients exhibited hypercalciuria, hypercalcemia, low parathyroid hormone, elevated vitamin D (1α,25(OH)2D3), normal 25-OHD3, decreased 24,25(OH)2D, and undetectable activity of 1,25(OH)2D-24-hydroxylase (CYP24A1), the enzyme that inactivates 1α,25(OH)2D3. Both patients had bi-allelic mutations in CYP24A1 leading to loss of function of this enzyme. On the basis of dbSNP data, the frequency of predicted deleterious bi-allelic CYP24A1 variants in the general population is estimated to be as high as 4%-20%.

CONCLUSIONS

The results of this study show that 1,25(OH)2D-24-hydroxylase deficiency due to bi-allelic mutations in CYP24A1 causes elevated serum vitamin D, hypercalciuria, nephrocalcinosis, and renal stones.

Cystinosis: the evolution of a treatable disease

Cystinosis is a rare autosomal recessive disorder involving lysosomal storage of the amino acid cystine due to a defect in the membrane transport protein, cystinosin. Since the introduction of kidney transplants and the availability of cystine-depleting medical therapy, this previously fatal disease was transformed into a treatable disorder. Renal allografts and medical therapy targeting the basic metabolic defect have altered the natural hisotry of cystinosis so drastically that patients have a life expectancy extending past 50 years. Consequently, early diagnosis and appropriate therapy are critically important. In this article, we offer a review of the manifestations of cystinosis, including the proximal tubular dysfunction of renal Fanconi syndrome, and discuss the prevention and treatment of the disorder's systemic complications. We focus on the nephropathic forms of cystinosis, aiming to assist nephrologists and other physicians to develop early recognition and appropriate management of cystinosis patients.

Characteristics of congenital hepatic fibrosis in a large cohort of patients with autosomal recessive polycystic kidney disease

BACKGROUND & AIMS

Autosomal recessive polycystic kidney disease (ARPKD), the most common ciliopathy of childhood, is characterized by congenital hepatic fibrosis and progressive cystic degeneration of kidneys. We aimed to describe congenital hepatic fibrosis in patients with ARPKD, confirmed by detection of mutations in PKHD1.

METHODS

Patients with ARPKD and congenital hepatic fibrosis were evaluated at the National Institutes of Health from 2003 to 2009. We analyzed clinical, molecular, and imaging data from 73 patients (age, 1-56 years; average, 12.7 ± 13.1 years) with kidney and liver involvement (based on clinical, imaging, or biopsy analyses) and mutations in PKHD1.

RESULTS

Initial symptoms were liver related in 26% of patients, and others presented with kidney disease. One patient underwent liver and kidney transplantation, and 10 others received kidney transplants. Four presented with cholangitis and one with variceal bleeding. Sixty-nine percent of patients had enlarged left lobes on magnetic resonance imaging, 92% had increased liver echogenicity on ultrasonography, and 65% had splenomegaly. Splenomegaly started early in life; 60% of children younger than 5 years had enlarged spleens. Spleen volume had an inverse correlation with platelet count and prothrombin time but not with serum albumin level. Platelet count was the best predictor of spleen volume (area under the curve of 0.88905), and spleen length corrected for patient's height correlated inversely with platelet count (R(2) = 0.42, P < .0001). Spleen volume did not correlate with renal function or type of PKHD1 mutation. Twenty-two of 31 patients who underwent endoscopy were found to have varices. Five had variceal bleeding, and 2 had portosystemic shunts. Forty-percent had Caroli syndrome, and 30% had an isolated dilated common bile duct.

CONCLUSIONS

Platelet count is the best predictor of the severity of portal hypertension, which has early onset but is underdiagnosed in patients with ARPKD. Seventy percent of patients with ARPKD have biliary abnormalities. Kidney and liver disease are independent, and variability in severity is not explainable by type of PKHD1 mutation; ClinicalTrials.gov number, NCT00068224.

Oral monosaccharide therapies to reverse renal and muscle hyposialylation in a mouse model of GNE myopathy

GNE myopathy, previously termed hereditary inclusion body myopathy (HIBM), is an adult-onset neuromuscular disorder characterized by progressive muscle weakness. The disorder results from biallelic mutations in GNE, encoding UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase, the key enzyme of sialic acid synthesis. GNE myopathy, associated with impaired glycan sialylation, has no approved therapy. Here we test potential sialylation-increasing monosaccharides for their effectiveness in prophylaxis (at the embryonic and neonatal stages) and therapy (after the onset of symptoms) by evaluating renal and muscle hyposialylation in a knock-in mouse model (Gne p.M712T) of GNE myopathy. We demonstrate that oral mannosamine (ManN), but not sialic acid (Neu5Ac), mannose (Man), galactose (Gal), or glucosamine (GlcN), administered to pregnant female mice has a similar prophylactic effect on renal hyposialylation, pathology and neonatal survival of mutant offspring, as previously shown for N-acetylmannosamine (ManNAc) therapy. ManN may be converted to ManNAc by a direct, yet unknown, pathway, or may act through another mode of action. The other sugars (Man, Gal, GlcN) may either not cross the placental barrier (Neu5Ac) and/or may not be able to directly increase sialylation. Because GNE myopathy patients will likely require treatment in adulthood after onset of symptoms, we also administered ManNAc (1 or 2g/kg/day for 12 weeks), Neu5Ac (2 g/kg/day for 12 weeks), or ManN (2 g/kg/day for 6 weeks) in drinking water to 6 month old mutant Gne p.M712T mice. All three therapies markedly improved the muscle and renal hyposialylation, as evidenced by lectin histochemistry for overall sialylation status and immunoblotting of specific sialoproteins. These preclinical data strongly support further evaluation of oral ManNAc, Neu5Ac and ManN as therapy for GNE myopathy and conceivably for certain glomerular diseases with hyposialylation.

An apparent homozygous deletion in maltase-glucoamylase, a lesson in the evolution of SNP arrays

Single nucleotide polymorphism (SNP) arrays possess clinical potential due to their high throughput capacity, sensitivity and versatility. We used such an array to perform a genome-wide SNP analysis of a patient with a multi-system undiagnosed disease involving peripheral neuropathies and food intolerances. The patient had a homozygous deletion within the gene encoding maltase-glucoamylase (MGAM), an intestinal starch digestion enzyme, predicting absence of enzyme activity and potential starch indigestion. We then performed validation testing using a functional MGAM analysis that involved starch ingestion followed by measuring blood glucose and insulin levels as well as hydrogen breath levels. Gastrointestinal tissue was also obtained via endoscopy and immunohistochemical staining for intestinal MGAM was performed. Our results strongly suggest the presence and functioning of MGAM which disproved deficiency predictions based on SNP array analysis findings, classifying the deletion as a functional polymorphism. This study highlights a current clinical limitation of SNP arrays, i.e., distinguishing deleterious genomic alterations from misleading functional polymorphisms. We conclude that novel findings from SNP arrays should be clinically validated and published.

Platelet-derived CD154: ultrastructural localization and clinical correlation in organ transplantation

CD154 is an immunostimulatory ligand for CD40 that markedly influences alloimmunity. Its presence in platelets suggests that its release and subsequent immune effects are driven by trauma and thus could be relevant following organ transplantation. However, the release of platelet derived CD154 and its consequences have not been investigated in a clinical transplant setting. To better characterize the relationship between platelet activation and CD154 release, we investigated CD154 release by platelets obtained from normal individuals, and patients with two genetic defects that influence platelet granule development. Using these unique patient populations and immune-electron microscopy, we confirmed that CD154 was an alpha granule and not a cell surface protein, and thereafter optimized the methods for its in vivo measurement in humans. We then investigated plasma CD154 levels in kidney and liver transplant recipients and found no evidence that CD154 levels fluctuated systemically as a result of kidney or liver transplant procedures. Paradoxically, we found that kidney transplant patients had significantly lower systemic CD154 levels during episodes of rejection. These data suggest that the immune effects of CD154 are likely mediated through local and not systemic mechanisms, and discourage the use of CD154 as a peripheral biomarker in organ transplantation.

The battlefield of rare diseases: where uncommon insights are common

The study of rare diseases reveals important insights about normal physiology and the pathogenesis of common disorders, pointing the way to new therapeutic options.

A BLOC-1 mutation screen reveals a novel BLOC1S3 mutation in Hermansky-Pudlak Syndrome type 8

Hermansky-Pudlak Syndrome (HPS) is a genetically heterogeneous disorder of lysosome-related organelle biogenesis and is characterized by oculocutaneous albinism and a bleeding diathesis. Over the past decade, we screened 250 patients with HPS-like symptoms for mutations in the genes responsible for HPS subtypes 1-6. We identified 38 individuals with no functional mutations, and therefore, we analyzed all eight genes encoding the biogenesis of lysosome-related organelles complex-1 (BLOC-1) proteins in these individuals. Here, we describe the identification of a novel nonsense mutation in BLOC1S3 (HPS-8) in a 6-yr-old Iranian boy. This mutation caused nonsense-mediated decay of BLOC1S3 mRNA and destabilized the BLOC-1 complex. Our patient's melanocytes showed aberrant localization of TYRP1, with increased plasma membrane trafficking. These findings confirm a common cellular defect for HPS patients with defects in BLOC-1 subunits. We identified only two patients with BLOC-1 defects in our cohort, suggesting that other HPS genes remain to be identified.

Rapid ultrastructural detection of success or failure after bone marrow transplantation in the Chediak-Higashi syndrome

The present study has used electron microscopic techniques to rapidly detect the success or failure of bone marrow transplantation in three patients with the Chediak-Higashi Syndrome (CHS). The most rapid procedure was the whole mount technique to determine the presence or absence of dense bodies, which are inherently electron-opaque, serotonin-containing storage organelles in platelets. Dense bodies were present in normal numbers in platelets from two patients with successful transplantation and absent in thrombocytes from another patient in whom the transplant had failed.

Exome sequencing as a diagnostic tool in a case of undiagnosed juvenile-onset GM1-gangliosidosis

OBJECTIVE

To utilize high-throughput sequencing to determine the etiology of juvenile-onset neurodegeneration in a 19-year-old woman with progressive motor and cognitive decline.

METHODS

Exome sequencing identified an initial list of 133,555 variants in the proband's family, which were filtered using segregation analysis, presence in dbSNP, and an empirically derived gene exclusion list. The filtered list comprised 52 genes: 21 homozygous variants and 31 compound heterozygous variants. These variants were subsequently scrutinized with predicted pathogenicity programs and for association with appropriate clinical syndromes.

RESULTS

Exome sequencing data identified 2 GLB1 variants (c.602G>A, p.R201H; c.785G>T, p.G262V). β-Galactosidase enzyme analysis prior to our evaluation was reported as normal; however, subsequent testing was consistent with juvenile-onset GM1-gangliosidosis. Urine oligosaccharide analysis was positive for multiple oligosaccharides with terminal galactose residues.

CONCLUSIONS

We describe a patient with juvenile-onset neurodegeneration that had eluded diagnosis for over a decade. GM1-gangliosidosis had previously been excluded from consideration, but was subsequently identified as the correct diagnosis using exome sequencing. Exome sequencing can evaluate genes not previously associated with neurodegeneration, as well as most known neurodegeneration-associated genes. Our results demonstrate the utility of "agnostic" exome sequencing to evaluate patients with undiagnosed disorders, without prejudice from prior testing results.

The BLOS1-interacting protein KXD1 is involved in the biogenesis of lysosome-related organelles

Biogenesis of lysosome-related organelles (LROs) complex-1 (BLOC-1) is an eight-subunit complex involved in lysosomal trafficking. Interacting proteins of these subunits expand the understanding of its biological functions. With the implementation of the naïve Bayesian analysis, we found that a human uncharacterized 20 kDa coiled-coil KxDL protein, KXD1, is a BLOS1-interacting protein. In vitro binding assays confirmed the interaction between BLOS1 and KXD1. The mouse KXD1 homolog was widely expressed and absent in Kxd1 knockout (KO) mice. BLOS1 was apparently reduced in Kxd1-KO mice. Mild defects in the melanosomes of the retinal pigment epithelia and in the platelet dense granules of the Kxd1-KO mouse were observed, mimicking a mouse model of mild Hermansky-Pudlak syndrome that affects the biogenesis of LROs.

Two novel CTNS mutations in cystinosis patients in Thailand

Cystinosis is an autosomal recessive disorder characterized by defective transport of cystine across the lysosomal membrane and resulting in renal, ophthalmic, and other organ abnormalities. Mutations in the CTNS gene cause a deficiency of the transport protein, cystinosin. We performed mutation analysis of CTNS in six cystinosis patients from four families in Thailand. Using PCR sequencing of the entire coding regions, we identified all eight mutant alleles, including two mutations, p.G309D and p.Q284X, that have not been previously reported. This study expands the mutational and population spectrum of nephropathic cystinosis.

Cysteamine suppresses invasion, metastasis and prolongs survival by inhibiting matrix metalloproteinases in a mouse model of human pancreatic cancer

Background

Cysteamine, an anti-oxidant aminothiol, is the treatment of choice for nephropathic cystinosis, a rare lysosomal storage disease. Cysteamine is a chemo-sensitization and radioprotection agent and its antitumor effects have been investigated in various tumor cell lines and chemical induced carcinogenesis. Here, we investigated whether cysteamine has anti-tumor and anti-metastatic effects in transplantable human pancreatic cancer, an aggressive metastatic disease.

Methodology/Principal Findings

Cysteamine's anti-invasion effects were studied by matrigel invasion and cell migration assays in 10 pancreatic cancer cell lines. To study mechanism of action, we examined cell viability and matrix metalloproteinases (MMPs) activity in the cysteamine-treated cells. We also examined cysteamine's anti-metastasis effect in two orthotopic murine models of human pancreatic cancer by measuring peritoneal metastasis and survival of animals. Cysteamine inhibited both migration and invasion of all ten pancreatic cancer cell lines at concentrations (<25 mM) that caused no toxicity to cells. It significantly decreased MMPs activity (IC₅₀ 38–460 µM) and zymographic gelatinase activity in a dose dependent manner in vitro and in vivo; while mRNA and protein levels of MMP-9, MMP-12 and MMP-14 were slightly increased using the highest cysteamine concentration. In vivo, cysteamine significantly decreased metastasis in two established pancreatic tumor models, although it did not affect the size of primary tumors. Additionally, cysteamine prolonged survival of mice in a dose-dependent manner without causing any toxicity. Similar to the in vitro results, MMP activity was significantly decreased in animal tumors treated with cysteamine. Cysteamine had no clinical or preclinical adverse effects in the host even at the highest dose.

Conclusions/Significance

Our results suggest that cysteamine, an agent with a proven safety profile, may be useful for inhibition of metastasis and prolonging the survival of a host with pancreatic cancer.

Sensitive quantification of mosaicism using high density SNP arrays and the cumulative distribution function

Medicine is rapidly applying exome and genome sequencing to the diagnosis and management of human disease. Somatic mosaicism, however, is not readily detectable by these means, and yet it accounts for a significant portion of undiagnosed disease. We present a rapid and sensitive method, the Continuous Distribution Function as applied to single nucleotide polymorphism (SNP) array data, to quantify somatic mosaicism throughout the genome. We also demonstrate application of the method to novel diseases and mechanisms.

Recombination mapping using Boolean logic and high-density SNP genotyping for exome sequence filtering

Whole genome sequence data for small pedigrees has been shown to provide sufficient information to resolve detailed haplotypes in small pedigrees. Using such information, recombinations can be mapped onto chromosomes, compared with the segregation of a disease of interest and used to filter genome sequence variants. We now show that relatively inexpensive SNP array data from small pedigrees can be used in a similar manner to provide a means of identifying regions of interest in exome sequencing projects. We demonstrate that in those situations where one can assume complete penetrance and parental DNA is available, SNP recombination mapping using Boolean logic identifies chromosomal regions identical to those detected by multipoint linkage using microsatellites but with much less computation. We further show that this approach is successful because the probability of a double crossover between informative SNP loci is negligible. Our observations provide a rationale for using SNP arrays and recombination mapping as a rapid and cost-effective means of incorporating chromosome segregation information into exome sequencing projects intended for disease-gene identification.

Analysis of DNA sequence variants detected by high-throughput sequencing

The Undiagnosed Diseases Program at the National Institutes of Health uses high-throughput sequencing (HTS) to diagnose rare and novel diseases. HTS techniques generate large numbers of DNA sequence variants, which must be analyzed and filtered to find candidates for disease causation. Despite the publication of an increasing number of successful exome-based projects, there has been little formal discussion of the analytic steps applied to HTS variant lists. We present the results of our experience with over 30 families for whom HTS sequencing was used in an attempt to find clinical diagnoses. For each family, exome sequence was augmented with high-density SNP-array data. We present a discussion of the theory and practical application of each analytic step and provide example data to illustrate our approach. The article is designed to provide an analytic roadmap for variant analysis, thereby enabling a wide range of researchers and clinical genetics practitioners to perform direct analysis of HTS data for their patients and projects.

An analysis of exome sequencing for diagnostic testing of the genes associated with muscle disease and spastic paraplegia

In this study, we assess exome sequencing (ES) as a diagnostic alternative for genetically heterogeneous disorders. Because ES readily identified a previously reported homozygous mutation in the CAPN3 gene for an individual with an undiagnosed limb girdle muscular dystrophy, we evaluated ES as a generalizable clinical diagnostic tool by assessing the targeting efficiency and sequencing coverage of 88 genes associated with muscle disease (MD) and spastic paraplegia (SPG). We used three exome-capture kits on 125 individuals. Exons constituting each gene were defined using the UCSC and CCDS databases. The three exome-capture kits targeted 47-92% of bases within the UCSC-defined exons and 97-99% of bases within the CCDS-defined exons. An average of 61.2-99.5% and 19.1-99.5% of targeted bases per gene were sequenced to 20X coverage within the CCDS-defined MD and SPG coding exons, respectively. Greater than 95-99% of targeted known mutation positions were sequenced to ≥1X coverage and 55-87% to ≥20X coverage in every exome. We conclude, therefore, that ES is a rapid and efficient first-tier method to screen for mutations, particularly within the CCDS annotated exons, although its application requires disclosure of the extent of coverage for each targeted gene and supplementation with second-tier Sanger sequencing for full coverage.

VAR-MD: a tool to analyze whole exome-genome variants in small human pedigrees with mendelian inheritance

The analysis of variants generated by exome sequencing (ES) of families with rare Mendelian diseases is a time-consuming, manual process that represents one barrier to applying the technology routinely. To address this issue, we have developed a software tool, VAR-MD (http://research.nhgri.nih.gov/software/var-md/), for analyzing the DNA sequence variants produced by human ES. VAR-MD generates a ranked list of variants using predicted pathogenicity, Mendelian inheritance models, genotype quality, and population variant frequency data. VAR-MD was tested using two previously solved data sets and one unsolved data set. In the solved cases, the correct variant was listed at the top of VAR-MD's variant ranking. In the unsolved case, the correct variant was highly ranked, allowing for subsequent identification and validation. We conclude that VAR-MD has the potential to enhance mutation identification using family based, annotated next generation sequencing data. Moreover, we predict an incremental advancement in software performance as the reference databases, such as Single Nucleotide Polymorphism Database and Human Gene Mutation Database, continue to improve.

Interstitial lung disease and pulmonary fibrosis in Hermansky-Pudlak syndrome type 2, an adaptor protein-3 complex disease

Pulmonary fibrosis develops in Hermansky-Pudlak syndrome (HPS) types 1 and 4. Limited information is available about lung disease in HPS type 2 (HPS-2), which is characterized by abnormal function of the adaptor protein-3 (AP-3) complex. To define lung disease in HPS-2, one child and two adults with HPS-2 were evaluated at the National Institutes of Health on at least two visits, and another child was evaluated at the University of Texas Health Science Center San Antonio. All four subjects with HPS-2 had findings of interstitial lung disease (ILD) on a high-resolution computed tomography scan of the chest. The predominant feature was ground glass opacification. Subject 1, a 14-year-old male, and subject 4, a 4-year-old male, had severe ILD, pulmonary fibrosis, secondary pulmonary hypertension and recurrent lung infections. Lung biopsy performed at 20 months of age in subject 1 revealed interstitial fibrosis and prominent type II pneumocyte hyperplasia without lamellar body enlargement. Subject 2, a 27-year-old male smoker, had mild ILD. Subject 3, a 22-year-old male nonsmoker and brother of subject 2, had minimal ILD. Severe impairment of gas exchange was found in subjects 1 and 4 and not in subjects 2 or 3. Plasma concentrations of transforming growth factor-β1 and interleukin-17A correlated with severity of HPS-2 ILD. These data show that children and young adults with HPS-2 and functional defects of the AP-3 complex are at risk for ILD and pulmonary fibrosis.

The Gne M712T mouse as a model for human glomerulopathy

Pathological glomerular hyposialylation has been implicated in certain unexplained glomerulopathies, including minimal change nephrosis, membranous glomerulonephritis, and IgA nephropathy. We studied our previously established mouse model carrying a homozygous mutation in the key enzyme of sialic acid biosynthesis, N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase. Mutant mice died before postnatal day 3 (P3) from severe glomerulopathy with podocyte effacement and segmental glomerular basement membrane splitting due to hyposialylation. Administration of the sialic acid precursor N-acetylmannosamine (ManNAc) led to improved sialylation and survival of mutant pups beyond P3. We determined the onset of the glomerulopathy in the embryonic stage. A lectin panel, distinguishing normally sialylated from hyposialylated glycans, used WGA, SNA, PNA, Jacalin, HPA, and VVA, indicating glomerular hyposialylation of predominantly O-linked glycoproteins in mutant mice. The glomerular glycoproteins nephrin and podocalyxin were hyposialylated in this unique murine model. ManNAc treatment appeared to ameliorate the hyposialylation status of mutant mice, indicated by a lectin histochemistry pattern similar to that of wild-type mice, with improved sialylation of both nephrin and podocalyxin, as well as reduced albuminuria compared with untreated mutant mice. These findings suggest application of our lectin panel for categorizing human kidney specimens based on glomerular sialylation status. Moreover, the partial restoration of glomerular architecture in ManNAc-treated mice highlights ManNAc as a potential treatment for humans affected with disorders of glomerular hyposialylation.

Aortic stenosis and vascular calcifications in alkaptonuria

Alkaptonuria is a rare metabolic disorder of tyrosine catabolism in which homogentisic acid (HGA) accumulates and is deposited throughout the spine, large joints, cardiovascular system, and various tissues throughout the body. In the cardiovascular system, pigment deposition has been described in the heart valves, endocardium, pericardium, aortic intima and coronary arteries. The prevalence of cardiovascular disease in patients with alkaptonuria varies in previous reports. We present a series of 76 consecutive adult patients with alkaptonuria who underwent transthoracic echocardiography between 2000 and 2009. A subgroup of 40 patients enrolled in a treatment study underwent non-contrast CT scans and these were assessed for vascular calcifications. Six of the 76 patients had aortic valve replacement. In the remaining 70 patients, 12 patients had aortic sclerosis and 7 patients had aortic stenosis. Unlike degenerative aortic valve disease, we found no correlation with standard cardiac risk factors. There was a modest association between the severity of aortic valve disease and joint involvement, however, we saw no correlation with urine HGA levels. Vascular calcifications were seen in the coronaries, cardiac valves, aortic root, descending aorta and iliac arteries. These findings suggest an important role for echocardiographic screening of alkaptonuria patients to detect valvular heart disease and cardiac CT to detect coronary artery calcifications.

The NIH Undiagnosed Diseases Program: bonding scientists and clinicians

The majority of the biomedical research workforce and funds are focused on studying common diseases and the development of drugs to treat them. However, some of the most remarkable discoveries in physiology and medicine are uncovered by studying rare conditions, because the importance of certain molecular mechanisms is revealed only when their dysfunction results in disease. In 2008, the National Institutes of Health (NIH) launched the NIH Undiagnosed Diseases Program (UDP), which recruits and selects patients who suffer from diseases of unknown etiology, and studies their causes at the clinical, genetic and cellular levels. In this Editorial, we discuss how the UDP has enabled the discovery of several new diseases and disease mechanisms through collaborations between clinical and basic science teams, using the power of both clinical medicine and biological models. Establishing programs with similar infrastructure at other centers around the world could help to benefit patients, their families and the entire medical community, by enhancing research productivity for rare and novel diseases.