Relation of synovitis to knee pain using contrast-enhanced MRIs.

BACKGROUND: It has been suggested that synovitis causes joint pain. On non-contrast-enhanced MRIs synovial thickening cannot be assessed and on these images synovitis has been inconsistently associated with pain. OBJECTIVE: To assess synovial thickening in relation to knee pain severity among subjects in the Multicenter Osteoarthritis Study (MOST) using contrast-enhanced (CE) MRI. METHODS: MOST is a cohort study of people who have, or are at high risk of, knee osteoarthritis (OA). An unselected subset of 535 participants who volunteered underwent CE 1.5 T MRI of one knee. Synovitis was scored in six compartments and a summary score was created. Knee pain severity was assessed using the maximum item score on the Western Ontario and McMaster Osteoarthritis Index (WOMAC) pain scale. The association between synovitis and pain severity was examined using a logistic regression model adjusting for age, sex, body mass index (BMI), MRI bone marrow lesions and effusions in the whole sample and in a subgroup without radiographic OA. RESULTS: 454 of the 535 subjects undergoing CE MRI had complete data on synovitis and WOMAC pain. Mean age was 59 years, mean BMI 30 and 48% were women. In knees with moderate pain, 80% had synovitis. For knee pain, synovitis conferred a 9.2-fold increased odds compared with those without synovitis. In knees without radiographic OA (n=329), there was also an association of synovitis with an increased prevalence of pain. CONCLUSION: Synovitis has a strong relation with knee pain severity, an association detected more clearly with CE MRI than suggested by previous studies using non-CE MRI measures of synovitis.

Clinical and cellular characterisation of Hermansky-Pudlak syndrome type 6.

BACKGROUND: In the last decade, Hermansky-Pudlak syndrome (HPS) has arisen as an instructive disorder for cell biologists to study the biogenesis of lysosome related organelles (LROs). Of the eight human HPS subtypes, only subtypes 1 through 5 are well described. AIM: To characterise extensively the HPS-6 subtype, caused by defects in HPS6, a subunit of the biogenesis of lysosome related organelles complex-2 (BLOC-2). METHODS: Mutation analysis for the HPS6 gene was performed on DNA from our group of unclassified HPS patients. The clinical phenotype of patients with HPS6 mutations was then carefully ascertained, and their cultured dermal melanocytes were employed for cellular immunofluorescence studies. RESULTS: Molecular studies showed a variety of mutations in the single exon HPS6 gene, including frame shift, missense, and nonsense mutations as well as a approximately 20 kb deletion spanning the entire HPS6 genomic region. Cellular studies revealed that the melanogenic proteins tyrosinase and tyrosinase related protein 1 failed to be efficiently delivered to the melanosomes of HPS-6 patients, explaining their hypopigmentation. Clinical studies indicated that HPS-6 patients exhibit oculocutaneous albinism and a bleeding diathesis. Importantly, granulomatous colitis and pulmonary fibrosis, debilitating features present in HPS subtypes 1 and 4, were not detected in our HPS-6 patients. CONCLUSION: The HPS-6 subtype resembles other BLOC-2 defective subtypes (that is, HPS-3 and HPS-5) in its molecular, cellular and clinical findings. These findings are not only important for providing a prognosis to newly diagnosed HPS-6 patients, but also for further elucidation of HPS function in the biogenesis of LROs.

Detection of hemizygosity in Hermansky-Pudlak syndrome by quantitative real-time PCR.

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder characterized by oculocutaneous albinism, a bleeding diathesis and, in some patients, pulmonary fibrosis or granulomatous colitis. HPS is associated with biosynthesis defects of melanosomes, platelet-dense bodies, and lysosomes. There are seven genetic HPS subtypes; HPS-1 is the most common. We used a real-time quantitative PCR (qPCR) approach to investigate six HPS-1 patients, previously assigned as having homozygous mutations in the HPS1 gene. HPS1 gene copy numbers, calculated by use of a comparative Ct method, revealed that one patient was in fact hemizygous for her c.1189delC (S396delC) HPS1 mutation. The causative deletion/insertion was 13,966 bp in size, with defined breakpoints, and involved an adjacent gene (C10orf33). A mechanism of formation is proposed for the deletion/insertion, and both multiplex and qPCR indicated that the deletion/insertion was present in the patient, her brother, and her father. qPCR amplification is valuable for detecting deletions too small to be identified by fluorescence in situ hybridization. This demonstration of hemizygosity, performed using genomic DNA, can eliminate concerns about non-paternity and can verify the diagnosis of an autosomal recessive disorder when a DNA alteration appears to be homozygous by standard PCR and sequencing methods, and its pathogenicity is in doubt.

Expression of CTNS alleles: subcellular localization and aminoglycoside correction in vitro.

Mutations in CTNS result in one of three forms of cystinosis: benign, intermediate, or nephropathic. Homozygosity for a nonsense mutation in CTNS (753G -->A), encoding a premature termination codon (PTC) at amino acid 138 (W138X), results in nephropathic cystinosis. Gentamicin is known to induce PTC readthrough and hence full-length protein production. We demonstrate that addition of gentamicin (300 microg/ml) to cystinotic fibroblasts leads to depletion of intracellular cystine in cell lines with a premature termination codon, but not in those with a large deletion or a deletion leading to a frameshift mutation. Plasmids were constructed with GFP as a C-terminal or N-terminal fusion to CTNS. The normal CTNS protein fused with either N- or C-terminal GFP colocalized with Lysotracker red, a fluorescent stain which selectively accumulates in lysosomes. PTC-GFP, a construct with GFP fused to the C-terminus of CTNS containing a PTC, allowed GFP to serve as a reporter of PTC readthrough. No significant fluorescence was observed in PTC-GFP-transfected cells in the absence of gentamicin but was seen and localized to lysosomes in its presence. A patient with a splice site mutation (IVS11 + 2T -->C) that eliminates the GYDQL lysosomal targeting sequence of cystinosin on one allele, and a PTC mutation (753G -->A) on the other, displays the intermediate phenotype. Transfection of the splice site mutant allele into CTNS null fibroblasts produced cystine depletion. Plasmids with GFP fused to the N-terminus of CTNS containing the splice site mutation (GFP-SS) were constructed. While the normal CTNS-GFP fusion protein was found to colocalize with Lysotracker red almost exclusively, the GFP-SS fusion product was found in the plasma membrane and cytoplasm, as well as lysosomes. A second lysosomal targeting motif in CTNS is present in this sequence, just proximal to the mutation, accounting for the partial lysosomal localization.