Linkage analysis of SLE susceptibility: confirmation of SLER1 at 5p15.3

We detected a novel susceptibility gene, SLER1, for systemic lupus erythematosus (SLE) at 5p15.3.(1) This finding was based on a selected subgroup of SLE families, where two or more family members have had alleged rheumatoid arthritis (SLE-RA). The main objective of this study was to replicate the linkage at 5p15.3 based on an independent data set of 88 SLE-RA families. Heterogeneity in the genetic model led us to use a nonparametric allele-sharing method. Since our a priori hypothesis of linkage at 5p15.3 was fixed, we genotyped six markers at the linked region. Our new results replicate the initial linkage at 5p15.3 (Zlr=2.58, P<0.005, LOD=1.45). Moreover, evidence of linkage was sustained when analysis was restricted to the subset of SLE families who had 3 or more individuals with alleged RA (Zlr=3.32, P=0.008, LOD=2.40) The results of our previous findings, together with these new results, confirm the SLER1 linkage at 5p15.3. Our results also demonstrate the utility of clinically defined subgroup analysis for detecting susceptibility loci for complex genetic diseases, such as SLE.     

Apoptotic cell death in mouse models of GM2 gangliosidosis and observations on human Tay-Sachs and Sandhoff diseases

Tay-Sachs and Sandhoff diseases are autosomal recessive neurodegenerative diseases resulting from the inability to catabolize GM2 ganglioside by beta-hexosaminidase A (Hex A) due to mutations of the alpha subunit (Tay-Sachs disease) or beta subunit (Sandhoff disease) of Hex A. Hex B (beta beta homodimer) is also defective in Sandhoff disease. We previously developed mouse models of both diseases and showed that Hexa-/- (Tay-Sachs) mice remain asymptomatic to at least 1 year of age while Hexb-/- (Sandhoff) mice succumb to a profound neurodegenerative disease by 4-6 months of age. Here we find that neuron death in Hexb-/- mice is associated with apoptosis occurring throughout the CNS, while Hexa-/- mice were minimally involved at the same age. Studies of autopsy samples of brain and spinal cord from human Tay-Sachs and Sandhoff diseases revealed apoptosis in both instances, in keeping with the severe expression of both diseases. We suggest that neuron death is caused by unscheduled apoptosis, implicating accumulated GM2 ganglioside or a derivative in triggering of the apoptotic cascade.      

Functional consequences of ROMK mutants linked to antenatal Bartter's syndrome and implications for treatment

The antenatal variant of Bartter's syndrome is an autosomal recessive kidney disease characterized by polyhydramnios, premature delivery, hypokalemic alkalosis and hypercalciuria. It is genetically heterogeneous, having been linked recently to mutations in an ATP- sensitive, renal outer medullary K+channel, ROMK, and earlier to mutations in the Na-K-2Cl co-transporter, NKCC2. We characterized four of the mutations reported in three heterozygous ROMK variants of antenatal Bartter's and found that each expressed a distinct phenotype in Sf9 cells. One mutation expressed normal function and appears to be an allelic polymorphism. The other three mutations produced channels with significantly reduced K+fluxes. However, the mechanisms in each case were different and reflected abnormalities in phosphorylation, proteolytic processing or protein trafficking. The different mechanisms may be important in the design of appropriate therapy for patients with this disease.      

Mutation of the gene encoding the enamel-specific protein, enamelin, causes autosomal-dominant amelogenesis imperfecta

Amelogenesis imperfecta (AI) is a group of inherited defects of dental enamel formation that shows both clinical and genetic heterogeneity. To date, mutations in the gene encoding amelogenin have been shown to underlie a subset of the X-linked recessive forms of AI. Although none of the genes underlying autosomal-dominant or autosomal-recessive AI have been identified, a locus for a local hypoplastic form has been mapped to human chromosome 4q11-q21. In the current investigation, we have analysed a family with an autosomal-dominant, smooth hypoplastic form of AI. Our results have shown that a splicing mutation in the splice donor site of intron 7 of the gene encoding the enamel-specific protein enamelin underlies the phenotype observed in this family. This is the first autosomal-dominant form of AI for which the genetic mutation has been identified. As this type of AI is clinically distinct from that localized previously to chromosome 4q11-q21, these findings highlight the need for a molecular classification of this group of disorders.     

Optimal degradation rate for collagen chambers used for regeneration of peripheral nerves over long gaps

The experimental study of peripheral nerve regeneration has depended heavily on the use of a nerve chamber in which the stumps of the transected nerve are inserted. A large variety of chamber fillings and chamber types have been used in an effort to induce a higher quality of regeneration across the gap initially separating the two stumps. In this study we studied the morphology of nerves regenerated across a 15 mm gap following implantation of a series of five chambers. The chambers were fabricated from type I collagen and possessed identical pore volume fractions as well as average pore diameters, but differed in cross-link density continuously along the series. The residual mass of the implanted chambers at 9 weeks was observed to increase continuously with increasing cross-link density along the series, indicating a continuous decrease in degradation rate. The quality of regenerated nerves, determined by the number of large diameter fibers (A-fibers) per nerve, the average diameter of all axons and the ratio of area occupied by axons (N-Ratio), was superior at an intermediate level of chamber degradation rate. The maximal quality of peripheral nerve regeneration corresponded to an optimal degradation rate with an estimated chamber half-life of approximately 2-3 weeks following implantation. A speculative mechanistic explanation of the observed optimum focuses on the hypothetical role of cell and cytokine traffic that may take place through holes in the chamber generated by the degradation process. The data show the presence of a hitherto unreported optimal chamber degradation rate that leads to regenerated nerves of maximum quality.     

Reproducible alteration of cytoplasmic polyhedrosis virus double-stranded RNA genome patterns on laboratory passage.

A change in the polyacrylamide gel electrophoretic pattern of the double-stranded RNA genome segments of a cytoplasmic polyhedrosis virus was observed following only one or two passages through laboratory-reared larvae of Heliothis armigera. This change consisted of the loss of a high molecular weight segment concomitant with the appearance of a low molecular weight segment and was a reproducible feature observed with several separate isolates from the field.