Structures of the HIN domain:DNA complexes reveal ligand binding and activation mechanisms of the AIM2 inflammasome and IFI16 receptor.

Recognition of DNA by the innate immune system is central to antiviral and antibacterial defenses, as well as an important contributor to autoimmune diseases involving self DNA. AIM2 (absent in melanoma 2) and IFI16 (interferon-inducible protein 16) have been identified as DNA receptors that induce inflammasome formation and interferon production, respectively. Here we present the crystal structures of their HIN domains in complex with double-stranded (ds) DNA. Non-sequence-specific DNA recognition is accomplished through electrostatic attraction between the positively charged HIN domain residues and the dsDNA sugar-phosphate backbone. An intramolecular complex of the AIM2 Pyrin and HIN domains in an autoinhibited state is liberated by DNA binding, which may facilitate the assembly of inflammasomes along the DNA staircase. These findings provide mechanistic insights into dsDNA as the activation trigger and oligomerization platform for the assembly of large innate signaling complexes such as the inflammasomes.

A BLOC-1 mutation screen reveals that PLDN is mutated in Hermansky-Pudlak Syndrome type 9.

Hermansky-Pudlak Syndrome (HPS) is an autosomal-recessive condition characterized by oculocutaneous albinism and a bleeding diathesis due to absent platelet delta granules. HPS is a genetically heterogeneous disorder of intracellular vesicle biogenesis. We first screened all our patients with HPS-like symptoms for mutations in the genes responsible for HPS-1 through HPS-6 and found no functional mutations in 38 individuals. We then examined all eight genes encoding the biogenesis of lysosome-related organelles complex-1, or BLOC-1, proteins in these individuals. This identified a homozygous nonsense mutation in PLDN in a boy with characteristic features of HPS. PLDN is mutated in the HPS mouse model pallid and encodes the protein pallidin, which interacts with the early endosomal t-SNARE syntaxin-13. We could not detect any full-length pallidin in our patient's cells despite normal mRNA expression of the mutant transcript. We could detect an alternative transcript that would skip the exon that harbored the mutation, but we demonstrate that if this transcript is translated into protein, although it correctly localizes to early endosomes, it does not interact with syntaxin-13. In our patient's melanocytes, the melanogenic protein TYRP1 showed aberrant localization, an increase in plasma-membrane trafficking, and a failure to reach melanosomes, explaining the boy's severe albinism and establishing his diagnosis as HPS-9.

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.

Homozygosity mapping and whole-exome sequencing to detect SLC45A2 and G6PC3 mutations in a single patient with oculocutaneous albinism and neutropenia.

We evaluated a 32-year-old woman whose oculocutaneous albinism (OCA), bleeding diathesis, neutropenia, and history of recurrent infections prompted consideration of the diagnosis of Hermansky-Pudlak syndrome type 2. This was ruled out because of the presence of platelet δ-granules and absence of AP3B1 mutations. As parental consanguinity suggested an autosomal recessive mode of inheritance, we employed homozygosity mapping, followed by whole-exome sequencing, to identify two candidate disease-causing genes, SLC45A2 and G6PC3. Conventional dideoxy sequencing confirmed pathogenic mutations in SLC45A2, associated with OCA type 4 (OCA-4), and G6PC3, associated with neutropenia. The substantial reduction of SLC45A2 protein in the patient's melanocytes caused the mislocalization of tyrosinase from melanosomes to the plasma membrane and also led to the incorporation of tyrosinase into exosomes and secretion into the culture medium, explaining the hypopigmentation in OCA-4. Our patient's G6PC3 mRNA expression level was also reduced, leading to increased apoptosis of her fibroblasts under endoplasmic reticulum stress. To our knowledge, this report describes the first North American patient with OCA-4, the first culture of human OCA-4 melanocytes, and the use of homozygosity mapping, followed by whole-exome sequencing, to identify disease-causing mutations in multiple genes in a single affected individual.

Dermatology and the Americans With Disabilities Act: a review of the case law.

The Americans With Disabilities Act (ADA) defines disability as a physical or mental impairment that substantially limits one or more major life activities. Although dermatology has received relatively little attention in the context of disability law, dermatologic diseases are properly covered by the ADA and are subject to the same criteria as other medical conditions. A Lexis-Nexis search of federal court decisions covering the ADA produced 23 cases dealing with dermatologic impairments as disabilities. In Cehrs v Northeast Ohio Alzheimer Research Center, a federal appeals court held that psoriasis constituted a disability under the Act. Skin diseases not only cause physical and mental impairments, but they are also visible to others. Persons with skin diseases may be "regarded as" disabled, and this can constitute discrimination under the law.