Spectrum of Perforin Gene Mutations in Familial Hemophagocytic Lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHL) is an autosomal recessive disease of early childhood characterized by nonmalignant accumulation and multivisceral infiltration of activated T lymphocytes and histiocytes (macrophages). Cytotoxic T and natural killer (NK) cell activity is markedly reduced or absent in these patients, and mutations in a lytic granule constituent, perforin, were recently identified in a number of FHL individuals. Here, we report a comprehensive survey of 34 additional patients with FHL for mutations in the coding region of the perforin gene and the relative frequency of perforin mutations in FHL. Perforin mutations were identified in 7 of the 34 families investigated. Six children were homozygous for the mutations, and one patient was a compound heterozygote. Four novel mutations were detected: one nonsense, two missense, and one deletion of one amino acid. In four families, a previously reported mutation at codon 374, causing a premature stop codon, was identified, and, therefore, this is the most common perforin mutation identified so far in FHL patients. We found perforin mutations in 20% of all FHL patients investigated (7/34), with a somewhat higher prevalence, ∼30% (6/20), in children whose parents originated from Turkey. No other correlation between the type of mutation and the phenotype of the patients was evident from the present study. Our combined results from mutational analysis of 34 families and linkage analysis of a subset of consanguineous families indicate that perforin mutations account for 20%–40% of the FHL cases and the FHL 1 locus on chromosome 9 for ∼10%, whereas the major part of the FHL cases are caused by mutations in not-yet-identified genes

Genetic studies of stroke in Northern Sweden

Stroke is a common disorder of later life with a complex etiology, including both environmental and genetic risk factors. The inherited predisposition is challenging to study due to the complexity of the stroke phenotype. Genetic studies in an isolated population have successfully identified a positional candidate gene for stroke, phosphodiesterase 4D (PDE4D). The aim of this thesis was to identify stroke susceptibility loci and positional candidate genes, taking advantage of low genetic variation in the northern Sweden population. All stroke cases were identified in a population-based stroke registry at the northern Sweden MONICA Centre. 56 families containing multiple cases of stroke and a follow up set of an additional 53 families were used for linkage studies. For association studies, 275 cases of first ever stroke together with 550 matched community controls were included. In paper I, we used a candidate region approach to investigate the PDE4D region on chromosome 5q. Linkage was obtained with a maximum allele-sharing LOD score of 2.06; P = 0.001. However, no significant association of ischemic stroke to the previously defined at-risk allele in PDE4D was observed. We next performed a genome wide linkage scan to explore new susceptibility loci for common forms of stroke (paper II). Non-parametric multipoint linkage analysis yielded allele-sharing LOD scores > 1.2 at nine locations; 1p34, 5q13, 7q35, 9q22, 9q34, 13q32, 14q32, 18p11, 20q13. The highest allele-sharing LOD score was obtained on chromosome 18p (LOD = 2.14). Fine mapping resulted in increased allele-sharing LOD scores for chromosome 5q13 and 9q22. In the follow up analysis of the nine regions, including all 109 families, the highest allele-sharing LOD scores were obtained on chromosomes 5q, 13q and 18p although none reached the initial genome wide values. In paper III, we focused on the chromosome 5q region, and further mapping and haplotype analysis in the families was performed. A common 1 cM haplotype was found to be shared among affected members of five families. In this region only the regulatory subunit 1 of phosphatidylinositol 3-kinase (PIK3R1) gene was located. Association of three single nucleotide polymorphisms in the PIK3R1 gene to common stroke was obtained in the case-control material. Finally, in paper IV, an extended pedigree containing seven families connected to common founders eight generations back was identified by genealogical analysis, and submitted to a separate genome wide scan analysis. A significant allele-sharing LOD score of 4.66 (genome wide P < 0.001) at chromosome 9q31-33 was obtained. Haplotype analysis identified a minimal common region of 3.2 cM, which was shared by four of the seven families. These four families contained all of the primary intracerebral hemorrhagic cases present in the extended pedigree. In conclusion we have replicated linkage of stroke susceptibility to the PDE4D region on chromosome 5q, but no significant association of ischemic stroke to PDE4D was observed. Linkage analysis of stroke did not identify any new major stroke loci, indicating that multiple minor susceptibility loci in addition to the previously known locus on chromosome 5q could contribute to the disease. In the chromosome 5q region a novel positional candidate gene for stroke was identified, the PIK3R1 gene. The PIK3R1 protein has several biological actions with potential roles in stroke susceptibility. Also a novel susceptibility locus for common forms of stroke at chromosome 9q was identified in a large pedigree, which may be of special importance for susceptibility to hemorrhagic stroke