Article

Clinical and cellular characterisation of Hermansky-Pudlak syndrome type 6

Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892-1851, USA.
Journal of Medical Genetics (Impact Factor: 6.34). 10/2009; 46(12):803-10. DOI: 10.1136/jmg.2008.065961
Source: PubMed

ABSTRACT

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.
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).
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.
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.
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.

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Available from: Amanda Helip-Wooley, Dec 22, 2015
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    • "The least understood HPS-associated complex is BLOC-2, comprised of subunits mutated in HPS types 3, 5, and 6 and their mouse models (Di Pietro et al., 2004; Gautam et al., 2004 ). BLOC-2 likely plays a regulatory role in LRO biogenesis , as BLOC-2–deficient HPS patients lack the lung pathology observed in BLOC-3– and AP-3–deficient patients (Huizing et al., 2009 ), and BLOC-2–deficient mice have less severe pigmentary and platelet aggregation defects than other HPS models (Novak et al., 1984Novak et al., , 1988 Zhang et al., 2003; Gautam et al., 2004). BLOC-2 subunits are conserved throughout vertebrate evolution (Daly et al., 2013) and in Drosophila melanogaster (Cheli and Dell'Angelica, 2010) but lack obvious structural features except for WD40 domains in HPS5 (Zhang et al., 2003) and a potential clathrin binding domain in HPS3 ( ). "
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    ABSTRACT: Hermansky-Pudlak syndrome (HPS) is a group of disorders characterized by the malformation of lysosome-related organelles, such as pigment cell melanosomes. Three of nine characterized HPS subtypes result from mutations in subunits of BLOC-2, a protein complex with no known molecular function. In this paper, we exploit melanocytes from mouse HPS models to place BLOC-2 within a cargo transport pathway from recycling endosomal domains to maturing melanosomes. In BLOC-2-deficient melanocytes, the melanosomal protein TYRP1 was largely depleted from pigment granules and underwent accelerated recycling from endosomes to the plasma membrane and to the Golgi. By live-cell imaging, recycling endosomal tubules of wild-type melanocytes made frequent and prolonged contacts with maturing melanosomes; in contrast, tubules from BLOC-2-deficient cells were shorter in length and made fewer, more transient contacts with melanosomes. These results support a model in which BLOC-2 functions to direct recycling endosomal tubular transport intermediates to maturing melanosomes and thereby promote cargo delivery and optimal pigmentation. © 2015 Dennis et al.
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    ABSTRACT: Hermansky-Pudlak syndrome (HPS) was first described in 1959 by Hermansky and Pudlak. Clinically, HPS is characterized by oculocutaneous albinism, platelet storage pool deficiency, and ceroid tissue accumulation. It is a rare disorder that has been described globally but has the highest frequency in a cluster population in Puerto Rico. HPS patients also have major organ involvement that typically includes pulmonary fibrosis and granulomatous colitis. Rarely have cardiomyopathy and renal dysfunction been described. We report a case of the oldest historical patient with HPS type 6 and the associated gastrointestinal management.
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