Biomedical subjects

A P Hsu

Publications and source records attributed to A P Hsu.

3 recordsLinked to original sources

PubMed2001

Primary immunodeficiency mutation databases.

Primary immunodeficiencies are intrinsic defects of immune systems. Mutations in a large number of cellular functions can lead to impaired immune responses. More than 80 primary immunodeficiencies are known to date. During the last years genes for several of these disorders have been identified. Here, mutation information for 23 genes affected in 14 immunodefects is presented. The proteins produced are employed in widely diverse functions, such as signal transduction, cell surface receptors, nucleotide metabolism, gene diversification, transcription factors, and phagocytosis. Altogether, the genetic defect of 2,140 families has been determined. Diseases with X-chromosomal origin constitute about 70% of all the cases, presumably due to full penetrance and because the single affected allele causes the phenotype. All types of mutations have been identified; missense mutations are the most common mutation type, and truncation is the most common effect on the protein level. Mutational hotspots in many disorders appear in CPG dinucleotides. The mutation data for the majority of diseases are distributed on the Internet with a special database management system, MUTbase. Despite large numbers of mutations, it has not been possible to make genotype-phenotype correlations for many of the diseases.

Alleles↗

PubMed2000

Efficient detection of thirty-seven new IL2RG mutations in human X-linked severe combined immunodeficiency.

X-linked severe combined immunodeficiency (XSCID) is a rare and potentially fatal disease caused by mutations of IL2RG, the gene encoding the interleukin-2 receptor gamma chain, a component of multiple cytokine receptors that are essential for lymphocyte development and function. To date, over 100 different mutations of IL2RG resulting in XSCID have been published. Using nonradioactive, direct DNA sequencing of a single PCR amplicon containing the whole IL2RG gene, we found IL2RG mutations in 78 previously unpublished unrelated cases of XSCID. We report 37 newly identified mutations of IL2RG, including 23 point mutations, 10 small deletions, 3 instances of the same single nucleotide insertion, 1 large deletion, and 2 complex mutations. More than half of the mutations (22 of 37) were predicted to result in unstable IL2RG mRNA. The remaining 14 mutations disrupted conserved functional motifs common to all cytokine receptor family members; changed protein conformation, charge, or hydrophobicity; or altered the intracellular portion of the protein, which is critical for proper interaction with signal-transducing molecules including Janus family tyrosine kinase 3.

Base Sequence↗

PubMed1999

Autoimmune lymphoproliferative syndrome with defective Fas: genotype influences penetrance.

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of lymphocyte homeostasis and immunological tolerance. Most patients have a heterozygous mutation in the APT1 gene, which encodes Fas (CD95, APO-1), mediator of an apoptotic pathway crucial to lymphocyte homeostasis. Of 17 unique APT1 mutations in unrelated ALPS probands, 12 (71%) occurred in exons 7-9, which encode the intracellular portion of Fas. In vitro, activated lymphocytes from all 17 patients showed apoptotic defects when exposed to an anti-Fas agonist monoclonal antibody. Similar defects were found in a Fas-negative cell line transfected with cDNAs bearing each of the mutations. In cotransfection experiments, Fas constructs with either intra- or extracellular mutations caused dominant inhibition of apoptosis mediated by wild-type Fas. Two missense Fas variants, not restricted to patients with ALPS, were identified. Variant A(-1)T at the Fas signal-sequence cleavage site, which mediates apoptosis less well than wild-type Fas and is partially inhibitory, was present in 13% of African American alleles. Among the ALPS-associated Fas mutants, dominant inhibition of apoptosis was much more pronounced in mutants affecting the intracellular, versus extracellular, portion of the Fas receptor. Mutations causing disruption of the intracellular Fas death domain also showed a higher penetrance of ALPS phenotype features in mutation-bearing relatives. Significant ALPS-related morbidity occurred in 44% of relatives with intracellular mutations, versus 0% of relatives with extracellular mutations. Thus, the location of mutations within APT1 strongly influences the development and the severity of ALPS.

Alleles↗