Positional cloning of a gene for Hermansky-Pudlak syndrome, a disorder of cytoplasmic organelles

Application of Forced Oscillation Technique in Assessing Pulmonary Fibrosis in Hermansky-Pudlak Syndrome

Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder characterized by defects in lysosome-related organelles. Given the high mortality rate associated with HPS pulmonary fibrosis (PF) and the significant risks tied to lung transplantation, it is essential to explore new tools for the early surveillance of PF to monitor its progression before clinical symptoms become apparent. This study evaluates the forced oscillation technique (FOT) for assessing PF in five adult patients with HPS, all homozygous for the HPS-1 (c.1472_1487dup p.His497Glnfs*90) founder mutation. Using the Resmon™ Pro V3 device, the FOT measured resistance (Rrs) and reactance (Xrs) at 5, 11, and 19 Hertz (Hz). High-resolution computed tomography (HRCT) scans of the chest were reviewed for radiographic findings. The cohort (n = 5) had a median age of 43 years. All patients exhibited HPS clinical features, including oculocutaneous albinism and respiratory symptoms such as dry cough and dyspnea. Radiographic analysis revealed PF in four patients (80%), with traction bronchiectasis, reticular patterns, honeycombing, and ground-glass opacities. The FOT detected progressive changes in pulmonary resistance and reactance correlating with fibrosis severity. These findings suggest that the FOT is a valuable non-invasive tool for monitoring PF in patients with HPS-1, potentially improving early diagnosis and management.

Enhanced MC1R-signalling and pH modulation facilitate melanogenesis within late endosomes of BLOC-1-deficient melanocytes

Photoprotective melanins in the skin are synthesised by epidermal melanocytes within specialised lysosome-related organelles called melanosomes. Melanosomes coexist with lysosomes; thus, melanocytes employ specific trafficking machineries to ensure correct cargo delivery to either the endolysosomal system or maturing melanosomes. Mutations in some of the protein complexes required for melanogenic cargo delivery, such as biogenesis of lysosome-related organelles complex 1 (BLOC-1), result in hypopigmentation due to mistrafficking of cargo to endolysosomes. We show that hypopigmented BLOC-1-deficient melanocytes retain melanogenic capacity that can be enhanced by treatment with cAMP elevating agents despite the mislocalisation of melanogenic proteins. The melanin formed in BLOC-1-deficient melanocytes is not generated in melanosomes but rather within late endosomes/lysosomes to which some cargoes mislocalise. Although these organelles generally are acidic, a cohort of late endosomes/lysosomes have a sufficiently neutral pH to facilitate melanogenesis, perhaps due to mislocalised melanosomal transporters and melanogenic enzymes. Modulation of the pH of late endosomes/lysosomes by genetic manipulation or via treatment with lysosomotropic agents significantly enhances the melanin content of BLOC-1-deficient melanocytes. Our data suggest that upregulation of mistargeted cargoes can facilitate reprogramming of a subset of endolysosomes to generate some functions of lysosome-related organelles.

Psychosocial implications of rare genetic skin diseases affecting appearance on daily life experiences, emotional state, self-perception and quality of life in adults: a systematic review

BACKGROUND

Since the beginning of human genetic research, there are very few publications sharing insights of the negative impact of rare genetic skin diseases (RGSD) on patients' experiences. This systematic review assessed the psychosocial implications of these conditions in terms of daily life experiences, emotional state, self-perception, and Quality of Life (QoL).

METHODOLOGY

A systematic review was carried out on albinism, neurofibromatosis type 1 (NF1), birthmarks and inherited ichthyosis. The PubMed, Scopus, PsycArticle, PsychInfo, Psychology and Behavioral Sciences Collection, and SOCindex databases were queried. Inclusion criteria were adult patients with one of these RGSDs. Simple descriptive statistics and qualitative content analysis were conducted to summarize the main results reported by the authors.

RESULTS

Of the 9987 articles retrieved, 48 articles were included: albinism (16), NF1 (16), inherited ichthyosis (10), birthmarks (6). The majority of the studies on albinism were conducted in Africa. Twenty-seven studies quantitatively assessed diverse psychological parameters: 13 showed a significant impact of the disease on QoL, five on emotional state, two on self-representation and two others on psychiatric comorbidities. Disease severity and visibility were good predictors of QoL (except for albinism). Body image and appearance concerns were also associated with QoL and emotional state. The 19 qualitative studies highlighted recurring themes across each of these diseases: discrimination and stigma during childhood and adolescence, discomfort in social interactions, guilt of transmission, the importance of social support from family and friends, altered daily life functioning, altered romantic and sex life, limited academic and professional aspirations, lack of interest and support from the medical field, and the unpredictability of the evolution of the disease. The only two mixed-method studies in this review were unable to contribute to any inferential analyses but could corroborate some of the qualitative findings.

CONCLUSION

These results showed that RGSDs have a significant impact on different aspects of patients' lives. This review has demonstrated that there is a real need for support systems for patients with these diseases. Such systems should be developed to provide them with necessary information and to guide them through an appropriate care pathway.

Genetics in Idiopathic Pulmonary Fibrosis: A Clinical Perspective

BACKGROUND

Unraveling the genetic background in a significant proportion of patients with both sporadic and familial IPF provided new insights into the pathogenic pathways of pulmonary fibrosis.

AIM

The aim of the present study is to overview the clinical significance of genetics in IPF.

PERSPECTIVE

It is fascinating to realize the so-far underestimated but dynamically increasing impact that genetics has on aspects related to the pathophysiology, accurate and early diagnosis, and treatment and prevention of this devastating disease. Genetics in IPF have contributed as no other in unchaining the disease from the dogma of a "a sporadic entity of the elderly, limited to the lungs" and allowed all scientists, but mostly clinicians, all over the world to consider its many aspects and "faces" in all age groups, including its co-existence with several extra pulmonary conditions from cutaneous albinism to bone-marrow and liver failure.

CONCLUSION

By providing additional evidence for unsuspected characteristics such as immunodeficiency, impaired mucus, and surfactant and telomere maintenance that very often co-exist through the interaction of common and rare genetic variants in the same patient, genetics have created a generous and pluralistic yet unifying platform that could lead to the understanding of the injurious and pro-fibrotic effects of many seemingly unrelated extrinsic and intrinsic offending factors. The same platform constantly instructs us about our limitations as well as about the heritability, the knowledge and the wisdom that is still missing.

Evolutionarily conserved role of hps1 in melanin production and blood coagulation in medaka fish

Hermansky–Pudlak syndrome is an autosomal recessive disease characterized by albinism, visual impairment, and blood platelet dysfunction. One of the genes responsible for Hermansky–Pudlak syndrome, hps1, regulates organelle biogenesis and thus plays important roles in melanin production, blood clotting, and the other organelle-related functions in humans and mice. However, the function of hps1 in other species remains poorly understood. In this study, we discovered albino medaka fish during the maintenance of a wild-derived population and identified hps1 as the responsible gene using positional cloning. In addition to the specific absence of melanophore pigmentation, the hps1 mutant showed reduced blood coagulation, suggesting that hps1 is involved in clotting caused by both mammalian platelets and fish thrombocytes. Together, the findings of our study demonstrate that hps1 has an evolutionarily conserved role in melanin production and blood coagulation. In addition, our study presents a useful vertebrate model for understanding the molecular mechanisms of Hermansky–Pudlak syndrome.

Oculocutaneous albinism and bleeding diathesis due to a novel deletion in the HPS3 gene

Hermansky–Pudlak syndrome (HPS) is a group of rare autosomal recessive disorders characterized by oculocutaneous albinism (OCA) and bleeding diathesis. To date, 11 HPS types have been reported (HPS-1 to HPS-11), each defined by disease-causing variants in specific genes. Variants in the HPS1 gene were found in approximately 15% of HPS patients, most of whom harbor the Puerto Rican founder mutation. In this study, we report six affected individuals from three nonconsanguineous families of Ashkenazi Jewish descent, who presented with OCA and multiple ecchymoses and had normal platelet number and size. Linkage analysis indicated complete segregation to HPS3. Sequencing of the whole coding region and the intron boundaries of HPS3 revealed a heterozygous c.1163+1G>A variant in all six patients. Long-range PCR amplification revealed that all affected individuals also carry a 14,761bp deletion that includes the 5′UTR and exon 1 of HPS3, encompassing regions with long interspersed nuclear elements. The frequency of the c.1163+1G>A splice site variant was found to be 1:200 in the Ashkenazi Jewish population, whereas the large deletion was not detected in 300 Ashkenazi Jewish controls. These results present a novel HPS3 deletion mutation and suggest that the prevalence of HPS-3 in Ashkenazi Jews is more common than previously thought.

Clinical Features and Novel Genetic Variants Associated with Hermansky-Pudlak Syndrome

Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive syndromic form of albinism, characterized by oculocutaneous albinism (OCA) and other systemic complications. The purpose of this study was to investigate patients with HPS-associated gene mutations and describe associated ocular and extraocular phenotypes. Fifty-four probands clinically diagnosed as albinism were enrolled. Ophthalmic examinations and genetic testing were performed in all subjects. The phenotypic and genetic features were evaluated. HPS-associated gene mutation was identified in four of the patients with albinism phenotype. Clinically, photophobia, and nystagmus was detected in all (4/4) patients, and strabismus was found in one (1/4) patient. Fundus examination revealed fundus hypopigmentation and foveal hypoplasia in all (8/8) eyes. Eight novel causative mutations were detected in these four HPS probands. Five (62.5%, 5/8) of the mutations were nonsense, two of the mutations were missense (25%, 2/8), and one of the mutations was frameshift (12.5%, 1/8). All patients in our study carried compound heterozygous variants, and all these pathogenic variants were identified to be novel, with most (62.5%, 5/8) of the mutations being nonsense. Our results improved the understanding of clinical ocular features, and expanded the spectrum of known variants and the genetic background of HPS.

New insights into the pathogenesis of Hermansky-Pudlak syndrome

Hermansky-Pudlak syndrome (HPS) is characterized by defects of multiple tissue-specific lysosome-related organelles (LROs), typically manifesting with oculocutaneous albinism or ocular albinism, bleeding tendency, and in some cases with pulmonary fibrosis, inflammatory bowel disease or immunodeficiency, neuropsychological disorders. Eleven HPS subtypes in humans and at least 15 subtypes in mice have been molecularly identified. Current understanding of the underlying mechanisms of HPS is focusing on the defective biogenesis of LROs. Compelling evidences have shown that HPS protein-associated complexes (HPACs) function in cargo transport, cargo recycling, and cargo removal to maintain LRO homeostasis. Further investigation on the molecular and cellular mechanism of LRO biogenesis and secretion will be helpful for better understanding of its pathogenesis and for the precise intervention of HPS.

Modeling of lung phenotype of Hermansky-Pudlak syndrome type I using patient-specific iPSCs

Background

Somatic cells differentiated from patient-specific human induced pluripotent stem cells (iPSCs) could be a useful tool in human cell-based disease research. Hermansky–Pudlak syndrome (HPS) is an autosomal recessive genetic disorder characterized by oculocutaneous albinism and a platelet dysfunction. HPS patients often suffer from lethal HPS associated interstitial pneumonia (HPSIP). Lung transplantation has been the only treatment for HPSIP. Lysosome-related organelles are impaired in HPS, thereby disrupting alveolar type 2 (AT2) cells with lamellar bodies. HPSIP lungs are characterized by enlarged lamellar bodies. Despite species differences between human and mouse in HPSIP, most studies have been conducted in mice since culturing human AT2 cells is difficult.

Methods

We generated patient-specific iPSCs from patient-derived fibroblasts with the most common bi-allelic variant, c.1472_1487dup16, in HPS1 for modeling severe phenotypes of HPSIP. We then corrected the variant of patient-specific iPSCs using CRISPR-based microhomology-mediated end joining to obtain isogenic controls. The iPSCs were then differentiated into lung epithelial cells using two different lung organoid models, lung bud organoids (LBOs) and alveolar organoids (AOs), and explored the phenotypes contributing to the pathogenesis of HPSIP using transcriptomic and proteomic analyses.

Results

The LBOs derived from patient-specific iPSCs successfully recapitulated the abnormalities in morphology and size. Proteomic analysis of AOs involving iPSC-derived AT2 cells and primary lung fibroblasts revealed mitochondrial dysfunction in HPS1 patient-specific alveolar epithelial cells. Further, giant lamellar bodies were recapitulated in patient-specific AT2 cells.

Conclusions

The HPS1 patient-specific iPSCs and their gene-corrected counterparts generated in this study could be a new research tool for understanding the pathogenesis of HPSIP caused by HPS1 deficiency in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01877-8.

A novel likely pathogenic variant in a patient with Hermansky-Pudlak syndrome

Hermansky-Pudlak syndrome (HPS) is a genetic disorder characterized by oculocutaneous albinism and variable pulmonary fibrosis, granulomatous colitis, or immunodeficiency. The diagnosis relies on clinical findings, platelet transmission electron microscopy studies showing absent dense granules, or the identification of a pathogenic genotype in one of 11 associated genes, including HPS1 We report a 2-wk-old male with significant iris transillumination defects, a pale fundus, and mild corectopia found by clinical exome sequencing to have a previously reported pathogenic variant, c.972dupC p.(Met325HisfsTer128), and a variant of uncertain significance, c.1846G>A p.(Glu616Lys), in HPS1 To determine whether his phenotype was consistent with HPS, follow-up studies of whole blood lumiaggregometry and platelet transmission electron microscopy were performed that revealed absent or markedly reduced platelet ATP secretion and virtually absent platelet dense granules, thus confirming the diagnosis. To the best of our knowledge, our case is the first in which the c.1846G>A p.(Glu616Lys) variant is identified in a patient with HPS. In addition, the case also highlights the importance of leveraging appropriate confirmatory clinical testing and reverse phenotyping, which allowed the care team to establish the clinical diagnosis of HPS and reclassify the previously reported variant of uncertain significance in HPS1 to likely pathogenic.

Inflammatory bowel disease in Hermansky-Pudlak syndrome: a retrospective single-centre cohort study

BACKGROUND

Knowledge about inflammatory bowel disease (IBD) in patients with Hermansky-Pudlak syndrome (HPS), a rare autosomal recessive disorder characterized by defective biogenesis of lysosome-related organelles, could provide insights into IBD in general.

OBJECTIVE

To expand the understanding of IBD in patients with HPS.

METHODS

Retrospective review of records from patients with HPS evaluated at the National Institutes of Health Clinical Center from 1995 to 2019 was conducted. Clinical features of IBD, genotyping results and histologic findings of colectomy specimens were analysed.

RESULTS

IBD affected 37 (14.2%; 12 male, 25 female) of 261 patients with HPS. Median age of onset was 17 years; range was 1 to 52 years. The most common symptoms of HPS IBD were hematochezia, abdominal pain and loose stools. Fistulae or extra-intestinal manifestations developed in 30% or 22%, respectively. Genotyping showed that patients with biallelic variants in HPS1, HPS3, HPS4 or HPS6 were diagnosed with IBD. Six children had very early-onset IBD. Patients with HPS-3 had mild manifestations of IBD. Medical therapy and bowel resection were utilized to treat 73% and 35% of patients with HPS IBD, respectively; 7 of 13 patients receiving anti-tumor necrosis factor alpha therapy had prolonged clinical responses. Active cryptitis, chronic inflammatory changes, granulomas and ceroid lipofuscinosis were histopathologic findings in three colectomy specimens.

CONCLUSIONS

IBD resembling Crohn's disease affects some patients with HPS; genetic heterogeneity is a feature of HPS IBD. HPS3 is a new gene associated with human IBD. Very early-onset IBD can develop in HPS.

Genetics of non-syndromic and syndromic oculocutaneous albinism in human and mouse

Oculocutaneous albinism (OCA) is the most frequent presentation of albinism, a heterogeneous rare genetic condition generally associated with variable alterations in pigmentation and with a profound visual impairment. There are non-syndromic and syndromic types of OCA, depending on whether the gene product affected impairs essentially the function of melanosomes or, in addition, that of other lysosome-related organelles (LROs), respectively. Syndromic OCA can be more severe and associated with additional systemic consequences, beyond pigmentation and vision alterations. In addition to OCA, albinism can also be presented without obvious skin and hair pigmentation alterations, in ocular albinism (OA), and a related genetic condition known as foveal hypoplasia, optic nerve decussation defects, and anterior segment dysgenesis (FHONDA). In this review, we will focus only in the genetics of skin pigmentation in OCA, both in human and mouse, updating our current knowledge on this subject.

Hermansky-Pudlak syndrome: Five Chinese patients with novel variants in HPS1 and HPS6

Hermansky-Pudlak syndrome is a rare, autosomal, recessive syndromic form of albinism characterized by oculocutaneous albinism, bleeding diathesis, and a series of clinical complications. It is rarely reported in China, even with its large population base. In this study, we describe the clinical phenotypes and genotypes of five unrelated Chinese Hermansky-Pudlak syndrome pedigrees following clinical observation and next-generation sequencing. We identified three HPS-1 and two HPS-6 cases among 548 Chinese patients with oculocutaneous albinism. Five novel variants [c.1279_1280insGGAG p.(Asp427Glyfs*27) and c.875_878delACAG p.(Asp292Alafs*38) in HPS1 and c.1999C>T p.(Arg667*), c.335G>A p.(W112*), and c.1732C>T p.(R578*) in HPS6] were identified by next-generation sequencing. Our findings expand the spectrum of known variants and the genetic background of Hermansky-Pudlak syndrome, which may help in investigating phenotype-genotype relationships and aid in genetic counselling of patients with Hermansky-Pudlak syndrome.

Hermansky-Pudlak syndrome pulmonary fibrosis: a rare inherited interstitial lung disease

Pulmonary fibrosis is a progressive interstitial lung disease of unknown aetiology with a poor prognosis. Studying genetic diseases associated with pulmonary fibrosis provides insights into the pathogenesis of the disease. Hermansky-Pudlak syndrome (HPS), a rare autosomal recessive disorder characterised by abnormal biogenesis of lysosome-related organelles, manifests with oculocutaneous albinism and excessive bleeding of variable severity. Pulmonary fibrosis is highly prevalent in three out of 10 genetic types of HPS (HPS-1, HPS-2 and HPS-4). Thus, genotyping of individuals with HPS is clinically relevant. HPS-1 tends to affect Puerto Rican individuals due to a genetic founder effect. HPS pulmonary fibrosis shares some clinical features with idiopathic pulmonary fibrosis (IPF), including dyspnoea, cough, restrictive lung physiology and computed tomography (CT) findings of fibrosis. In contrast to IPF, HPS pulmonary fibrosis generally affects children (HPS-2) or middle-aged adults (HPS-1 or HPS-4) and may be associated with ground-glass opacification in CT scans. Histopathology of HPS pulmonary fibrosis, and not IPF, shows vacuolated hyperplastic type II cells with enlarged lamellar bodies and alveolar macrophages with lipofuscin-like deposits. Antifibrotic drugs approved as treatment for IPF are not approved for HPS pulmonary fibrosis. However, lung transplantation has been performed in patients with severe HPS pulmonary fibrosis. HPS pulmonary fibrosis serves as a model for studying fibrotic lung disease and fibrosis in general.

Genetic analysis and prenatal diagnosis of 20 Chinese families with oculocutaneous albinism

Background

Oculocutaneous albinism (OCA) is a group of heterogeneous genetic disorders characterized by abnormal melanin synthesis in the hair, skin, and eyes. OCA exhibits obvious genetic and phenotypic heterogeneity. Molecular diagnosis of causal genes can be of help in the classification of OCA subtypes and the study of OCA pathogenesis．

Methods

In this study, Sanger sequencing and whole exome sequencing were used to genetically diagnose 20 nonconsanguineous Chinese OCA patients. In addition, prenatal diagnosis was provided to six OCA families.

Results

Variants of TYR, OCA2, and HPS1 were detected in 85%, 10%, and 5% of affected patients, respectively. A total of 21 distinct variants of these three genes were identified. Exons 1 and 2 were the hotspot regions of the TYR variants, and c.895C > A and c.896G > A were the hotspot variants. We also found seven novel variants: c.731G > A, c.741C > A, c.867C > A, and c.1037‐2A > T in TYR, c.695dupT and c.1054A > G in OCA2, and c.9C > A in HPS1. Genetic tests on six fetuses revealed three carrier fetuses, two normal fetuses, and one affected fetus. The follow‐up results after birth were consistent with the results of prenatal diagnosis (one fetus terminated during pregnancy was not followed up).

Conclusions

This study expands our understanding of the genotypic spectrum of the Chinese OCA population. The findings indicate that prenatal diagnosis can provide important information for genetic counseling.

Rab GTPases: Key players in melanosome biogenesis, transport, and transfer

Melanosomes are specialized intracellular organelles that produce and store melanin pigments in melanocytes, which are present in several mammalian tissues and organs, including the skin, hair, and eyes. Melanosomes form and mature stepwise (stages I-IV) in melanocytes and then are transported toward the plasma membrane along the cytoskeleton. They are subsequently transferred to neighboring keratinocytes by a largely unknown mechanism, and incorporated melanosomes are transported to the perinuclear region of the keratinocytes where they form melanin caps. Melanocytes also extend several dendrites that facilitate the efficient transfer of the melanosomes to the keratinocytes. Since the melanosome biogenesis, transport, and transfer steps require multiple membrane trafficking processes, Rab GTPases that are conserved key regulators of membrane traffic in all eukaryotes are crucial for skin and hair pigmentation. Dysfunctions of two Rab isoforms, Rab27A and Rab38, are known to cause a hypopigmentation phenotype in human type 2 Griscelli syndrome patients and in chocolate mice (related to Hermansky-Pudlak syndrome), respectively. In this review article, I review the literature on the functions of each Rab isoform and its upstream and downstream regulators in mammalian melanocytes and keratinocytes.

Current landscape of Oculocutaneous Albinism in Japan

Oculocutaneous albinism (OCA), which is roughly divided into non-syndromic and syndromic OCA, is a group of autosomal recessive disorders caused by mutations in genes associated with pigmentation. Patients with OCA have hypopigmentation and ocular manifestations such as photophobia, amblyopia, and nystagmus. Hermansky-Pudlak syndrome (HPS), the most common syndromic OCA, is characterized by the additional features of a bleeding tendency and other critical systemic comorbidities such as pulmonary fibrosis and immunodeficiency. NGS-based gene analyses have identified several new causative genes for OCA and have detected rare subtypes of OCA with high accuracy including Japanese patients. In our survey of 190 Japanese OCA patients/families, OCA4 is the most common subtype (25.3%) followed by OCA1 (20.0%), HPS1 (14.7%), and OCA2 (8.4%). Similar to the A481T variant in OCA2, which is associated with a mild form of OCA2 and skin color variation, the c.-492_489delAATG variant located in the promoter region of SLC45A2 has been uniquely identified in Japanese patients with a mild form of OCA4. Further, rare OCA subtypes, including OCA3, HPS2, HPS3, HPS4, HPS5, HPS6, and HPS9, have also been identified in Japanese patients. The clinical characteristics and underlying molecular mechanisms of each subtype of OCA are concisely summarized in this review.

Membrane trafficking in health and disease

Membrane trafficking pathways are essential for the viability and growth of cells, and play a major role in the interaction of cells with their environment. In this At a Glance article and accompanying poster, we outline the major cellular trafficking pathways and discuss how defects in the function of the molecular machinery that mediates this transport lead to various diseases in humans. We also briefly discuss possible therapeutic approaches that may be used in the future treatment of trafficking-based disorders.

Summary: This At a Glance article and poster summarise the major intracellular membrane trafficking pathways and associated molecular machineries, and describe how defects in these give rise to disease in humans.

Hermansky-Pudlak syndrome: Mutation update

Hermansky-Pudlak syndrome (HPS) is a group of 10 autosomal recessive multisystem disorders, each defined by the deficiency of a specific gene. HPS-associated genes encode components of four ubiquitously expressed protein complexes: Adaptor protein-3 (AP-3) and biogenesis of lysosome-related organelles complex-1 (BLOC-1) through -3. All individuals with HPS exhibit albinism and a bleeding diathesis; additional features occur depending on the defective protein complex. Pulmonary fibrosis is associated with AP-3 and BLOC-3 deficiency, immunodeficiency with AP-3 defects, and gastrointestinal symptoms are more prevalent and severe in BLOC-3 deficiency. Therefore, identification of the HPS subtype is valuable for prognosis, clinical management, and treatment options. The prevalence of HPS is estimated at 1-9 per 1,000,000. Here we summarize 264 reported and novel variants in 10 HPS genes and estimate that ~333 Puerto Rican HPS subjects and ~385 with other ethnicities are reported to date. We provide pathogenicity predictions for missense and splice site variants and list variants with high minor allele frequencies. Current cellular and clinical aspects of HPS are also summarized. This review can serve as a manifest for molecular diagnostics and genetic counseling aspects of HPS.

Clinical and genetic variability in children with partial albinism

Individuals who have ocular features of albinism and skin pigmentation in keeping with their familial background present a considerable diagnostic challenge. Timely diagnosis through genomic testing can help avert diagnostic odysseys and facilitates accurate genetic counselling and tailored specialist management. Here, we report the clinical and gene panel testing findings in 12 children with presumed ocular albinism. A definitive molecular diagnosis was made in 8/12 probands (67%) and a possible molecular diagnosis was identified in a further 3/12 probands (25%). TYR was the most commonly mutated gene in this cohort (75% of patients, 9/12). A disease-causing TYR haplotype comprised of two common, functional polymorphisms, TYR c.[575 C > A;1205 G > A] p.[(Ser192Tyr);(Arg402Gln)], was found to be particularly prevalent. One participant had GPR143-associated X-linked ocular albinism and another proband had biallelic variants in SLC38A8, a glutamine transporter gene associated with foveal hypoplasia and optic nerve misrouting without pigmentation defects. Intriguingly, 2/12 individuals had a single, rare, likely pathogenic variant in each of TYR and OCA2 - a significant enrichment compared to a control cohort of 4046 individuals from the 100,000 genomes project pilot dataset. Overall, our findings highlight that panel-based genetic testing is a clinically useful test with a high diagnostic yield in children with partial/ocular albinism.

Gene-edited MLE-15 Cells as a Model for the Hermansky-Pudlak Syndromes

Defining the mechanisms of cellular pathogenesis in rare lung diseases such as Hermansky-Pudlak syndrome (HPS) is often complicated by loss of the differentiated phenotype of cultured primary alveolar type 2 (AT2) cells, as well as by a lack of durable cell lines that are faithful to both AT2-cell and rare disease phenotypes. We used CRISPR/Cas9 gene editing to generate a series of HPS-specific mutations in the MLE-15 cell line. The resulting MLE-15/HPS cell lines exhibit preservation of AT2 cellular functions, including formation of lamellar body-like organelles, complete processing of surfactant protein B, and known features of HPS specific to each trafficking complex, including loss of protein targeting to lamellar bodies. MLE-15/HPS1 and MLE-15/HPS2 (with a mutation in Ap3β1) express increased macrophage chemotactic protein-1, a well-described mediator of alveolitis in patients with HPS and in mouse models. We show that MLE-15/HPS9 and pallid AT2 cells (with a mutation in Bloc1s6) also express increased macrophage chemotactic protein-1, suggesting that mice and humans with BLOC-1 mutations may also be susceptible to alveolitis. In addition to providing a flexible platform to examine the role of HPS-specific mutations in trafficking AT2 cells, MLE-15/HPS cell lines provide a durable resource for high-throughput screening and studies of cellular pathophysiology that are likely to accelerate progress toward developing novel therapies for this rare lung disease.

Stem Cell-Derived Models of Neural Crest Are Essential to Understand Melanoma Progression and Therapy Resistance

During development, neural crest (NC) cells are early precursors of several lineages including melanocytes. Along their differentiation from multipotent cells to mature melanocytes, NC cells will go through successive steps which require either proliferative or motile capacities. For example, they will undergo Epithelial to Mesenchymal Transition (EMT) in order the separate from the neural tube and migrate to their final location in the epidermis (Larribere and Utikal, 2013; Skrypek et al., 2017). The differentiated melanocytes are the cells of origin of melanoma tumors which progress through several stages such as radial growth phase, vertical growth phase, metastasis formation, and often resistance to current therapies. Interestingly, depending on the stage of the disease, melanoma tumor cells share phenotypes with NC cells (proliferative, motile, EMT). These phenotypes are tightly controlled by specific signaling pathways and transcription factors (TFs) which tend to be reactivated during the onset of melanoma. In this review, we summarize first the main TFs which control these common phenotypes. Then, we focus on the existing strategies used to generate human NCs. Finally we discuss how identification and regulation of NC-associated genes provide an additional approach to improving current melanoma targeted therapies.

Precise therapeutic gene correction by a simple nuclease-induced double-stranded break

Current programmable nuclease-based (e.g. CRISPR-Cas9) methods for precise correction of a disease-causing genetic mutation harness the Homology Directed Repair (HDR) pathway. However, this repair process requires co-delivery of an exogenous DNA donor to recode the sequence and can be inefficient in many cell types. Here, we show that disease-causing frameshift mutations resulting from microduplications can be efficiently reverted to the wild-type sequence simply by generating a double-strand break (DSB) near the center of the duplication. We demonstrate this in patient-derived cell lines for two diseases: Limb-Girdle Muscular Dystrophy 2G (LGMD2G)¹ and Hermansky-Pudlak Syndrome Type 1 (HPS1)². Clonal analysis of Streptococcus pyogenes Cas9 (SpyCas9) nuclease-treated LGMD2G iPSCs revealed that ~80% contained at least one wild-type allele and that this correction restored TCAP expression in LGMD2G iPSC-derived myotubes. Efficient genotypic correction was also observed upon SpyCas9 treatment of an HPS1 patient-derived B-lymphoblastoid cell line (B-LCL). Inhibition of PARP-1 (poly (ADP-ribose) polymerase) suppresses the nuclease-mediated collapse of the microduplication to the wild-type sequence, confirming that precise correction is mediated by the MMEJ (microhomology-mediated end joining) pathway. Analysis of editing by SpyCas9 and Lachnospiraceae bacterium ND2006 Cas12a (LbaCas12a) at non-pathogenic microduplications within the genome that range in length from 4 bp to 36 bp indicates that the correction strategy is broadly applicable to a wide range of microduplication lengths and can be initiated by a variety of nucleases. The simplicity, reliability and efficacy of this MMEJ-based therapeutic strategy should permit the development of nuclease-based gene correction therapies for a variety of diseases that are associated with microduplications.

Bleeding assessment in female patients with the Hermansky-Pudlak syndrome-A case series

INTRODUCTION

The Hermansky-Pudlak syndrome (HPS) is an autosomal recessive rare disorder characterized by oculocutaneous albinism, bleeding diathesis, chronic granulomatous colitis and/or pulmonary fibrosis. HPS is the most common single-gene disorder in Puerto Rico with a prevalence of 1:1,800 in the Northwest of the island. Risk of menorrhagia and post-partum hemorrhage (PPH) in cases of women with HPS have been described in the medical literature, but data regarding comprehensive description of bleeding diathesis remains lacking. For this reason, we aim to identify bleeding events using the International Society on Thrombosis and Hemostasis Bleeding Assessment Tool (ISTH-BAT), a standardized quantitative tool that translates the range of severity of bleeding symptoms into a cumulative bleeding score (BS).

OBJECTIVE

To use the ISTH-BAT in HPS in order to describe bleeding symptoms and allow for comparison with other inherited bleeding disorders.

METHODS

Puerto Rican females and adult participants with HPS based on genetic linkage were enrolled. The ISTH-BAT was administered and results were identified using descriptive statistical analysis.

RESULTS

Questionnaire answers of twelve women with HPS-1 and HPS-3 were evaluated. Participants' mean BS was HPS-1 (11.4) and HPS-3 (8.0) Participants with HPS-1 and HPS-3 reported abnormal bleeding events that presented during dental extractions, menorrhagia, surgical interventions, gastrointestinal, oral cavity and post-partum. Patients with history of pulmonary fibrosis (PF) showed a higher mean bleeding score than those who had no history of PF.

CONCLUSIONS

Female patients with HPS type 1 and 3 experienced abnormal bleeding events according to the ISTH-BAT bleeding score. Bleeding medications were inconsistently used and varied independently from healthcare professionals. The benefits of this study were to understand the history of bleeding complications in patients with HPS type 1 and 3 using an international validated system. The results of this study will help design strategies to improve the care we provide to this population.

Use of Targeted High-Throughput Sequencing for Genetic Classification of Patients with Bleeding Diathesis and Suspected Platelet Disorder

Inherited platelet disorders (IPD) form a rare and heterogeneous disease entity that is present in about 8% of patients with non-acquired bleeding diathesis. Identification of the defective cellular pathway is an important criterion for stratifying the patient's individual risk profile and for choosing personalized therapeutic options. While costs of high-throughput sequencing technologies have rapidly declined over the last decade, molecular genetic diagnosis of bleeding and platelet disorders is getting more and more suitable within the diagnostic algorithms. In this study, we developed, verified, and evaluated a targeted, panel-based next-generation sequencing approach comprising 59 genes associated with IPD for a cohort of 38 patients with a history of recurrent bleeding episodes and functionally suspected, but so far genetically undefined IPD. DNA samples from five patients with genetically defined IPD with disease-causing variants in WAS , RBM8A , FERMT3 , P2YR12 , and MYH9 served as controls during the validation process. In 40% of 35 patients analyzed, we were able to finally detect 15 variants, eight of which were novel, in 11 genes, ACTN1 , AP3B1 , GFI1B , HPS1 , HPS4 , HPS6 , MPL , MYH9 , TBXA2R , TPM4 , and TUBB1 , and classified them according to current guidelines. Apart from seven variants of uncertain significance in 11% of patients, nine variants were classified as likely pathogenic or pathogenic providing a molecular diagnosis for 26% of patients. This report also emphasizes on potentials and pitfalls of this tool and prospectively proposes its rational implementation within the diagnostic algorithms of IPD.

Predictable and precise template-free CRISPR editing of pathogenic variants

Following Cas9 cleavage, DNA repair without a donor template is generally considered stochastic, heterogeneous and impractical beyond gene disruption. Here, we show that template-free Cas9 editing is predictable and capable of precise repair to a predicted genotype, enabling correction of disease-associated mutations in humans. We constructed a library of 2,000 Cas9 guide RNAs paired with DNA target sites and trained inDelphi, a machine learning model that predicts genotypes and frequencies of 1- to 60-base-pair deletions and 1-base-pair insertions with high accuracy (r = 0.87) in five human and mouse cell lines. inDelphi predicts that 5-11% of Cas9 guide RNAs targeting the human genome are 'precise-50', yielding a single genotype comprising greater than or equal to 50% of all major editing products. We experimentally confirmed precise-50 insertions and deletions in 195 human disease-relevant alleles, including correction in primary patient-derived fibroblasts of pathogenic alleles to wild-type genotype for Hermansky-Pudlak syndrome and Menkes disease. This study establishes an approach for precise, template-free genome editing.

Prolonged treatment with open-label pirfenidone in Hermansky-Pudlak syndrome pulmonary fibrosis

PURPOSE

Limited information is available regarding chronic treatment with pirfenidone, an anti-fibrotic drug. Effects of long-term open-label pirfenidone were evaluated in a small cohort with Hermansky-Pudlak syndrome (HPS), a rare autosomal recessive disorder with highly penetrant pulmonary fibrosis.

RESULTS

Three patients with HPS pulmonary fibrosis treated with open-label pirfenidone and twenty-one historical controls randomized to placebo were studied at a single center. Mean duration of treatment with pirfenidone for 3 patients with HPS pulmonary fibrosis was 13.1 years. Annual changes in FVC and DLCO with pirfenidone treatment were 0.46 and - 0.93% predicted, respectively. In comparison, historical controls randomized to receive placebo experienced mean annual changes in FVC and DLCO of -4.4 and - 2.3% predicted, respectively. High-resolution computed tomography (HRCT) scans revealed improved ground glass opacities with development of minimal interstitial reticulations in 1 patient after 12.8 years of treatment with pirfenidone. Slowly progressive increase in bilateral interstitial fibrosis developed in a different patient, who received pirfenidone for 18.1 years and died at 73 years of age due to HPS pulmonary fibrosis. Another patient treated with pirfenidone for 8.4 years had attenuated ground glass opacification on HRCT scan and improved oxygenation; this patient died due to chronic complications from colitis, and not pulmonary fibrosis. Adverse effects were generally limited to mild gastrointestinal discomfort and transient elevations of alanine aminotransferase in one patient.

CONCLUSIONS

Chronic treatment with pirfenidone may provide clinical benefit with few adverse effects for some patients with HPS pulmonary fibrosis. These results suggest that compassionate use of pirfenidone could be considered on a case-by-case basis for patients with HPS pulmonary fibrosis.

Clinical management and outcomes of patients with Hermansky-Pudlak syndrome pulmonary fibrosis evaluated for lung transplantation

Pulmonary fibrosis is a progressive, fatal manifestation of Hermansky-Pudlak syndrome (HPS). Some patients with advanced HPS pulmonary fibrosis undergo lung transplantation despite their disease-associated bleeding tendency; others die while awaiting donor organs. The objective of this study is to determine the clinical management and outcomes of a cohort with advanced HPS pulmonary fibrosis who were evaluated for lung transplantation. Six patients with HPS-1 pulmonary fibrosis were evaluated at the National Institutes of Health Clinical Center and one of two regional lung transplant centers. Their median age was 41.5 years pre-transplant. Three of six patients died without receiving a lung transplant. One of these was referred with end-stage pulmonary fibrosis and died before a donor organ became available, and donor organs were not identified for two other patients sensitized from prior blood product transfusions. Three of six patients received bilateral lung transplants; they did not have a history of excessive bleeding. One patient received peri-operative desmopressin, one was transfused with intra-operative platelets, and one received extracorporeal membrane oxygenation and intra-operative prothrombin complex concentrate, platelet transfusion, and desmopressin. One transplant recipient experienced acute rejection that responded to pulsed steroids. No evidence of chronic lung allograft dysfunction or recurrence of HPS pulmonary fibrosis was detected up to 6 years post-transplant in these three lung transplant recipients. In conclusion, lung transplantation and extracorporeal membrane oxygenation are viable options for patients with HPS pulmonary fibrosis. Alloimmunization in HPS patients is an important and potentially preventable barrier to lung transplantation; interventions to limit alloimmunization should be implemented in HPS patients at risk of pulmonary fibrosis to optimize their candidacy for future lung transplants.

Hermansky-Pudlak syndrome: Report of two patients with updated genetic classification and management recommendations

Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder caused by mutations in one of nine genes involved in the packaging and formation of specialized lysosomes, including melanosomes and platelet-dense granules. The cardinal features are pigmentary dilution, bleeding diathesis, and accumulation of ceroid-like material in reticuloendothelial cells. Pulmonary fibrosis induced by tissue damage is seen in the most severe forms, and one subtype is characterized by immunodeficiency. We describe two patients with HPS type 1 and review the updated gene-based classification, clinical features, and recommendations for evaluation and follow-up.

Pulmonary Fibrosis in Hermansky-Pudlak Syndrome

Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive genetic disorder characterized by oculocutaneous albinism and a bleeding diathesis due to platelet dysfunction. More than 50% of cases worldwide are diagnosed on the Caribbean island of Puerto Rico. Genetic testing plays a growing role in diagnosis; however, not all patients with HPS have identified genetic mutations. In Puerto Rico, patients with HPS are often identified shortly after birth by their albinism, although the degree of hypopigmentation is highly variable. Ten subtypes have been described. Patients with HPS-1, HPS-2, and HPS-4 tend to develop pulmonary fibrosis in Puerto Rico; 100% of patients with HPS-1 develop HPS-PF. HPS-PF and idiopathic pulmonary fibrosis are considered similar entities (albeit with distinct causes) because both can show similar histological disease patterns. However, in contrast to idiopathic pulmonary fibrosis, HPS-PF manifests much earlier, often at 30-40 years of age. The progression of HPS-PF is characterized by the development of dyspnea and increasingly debilitating hypoxemia. No therapeutic interventions are currently approved by the U.S. Food and Drug Administration for the treatment of HPS and HPS-PF. However, the approval of two new antifibrotic drugs, pirfenidone and nintedanib, has prompted new interest in identifying drugs capable of reversing or halting the progression of HPS-PF. Thus, lung transplantation remains the only potentially life-prolonging treatment. At present, two clinical trials are recruiting patients with HPS-PF to identify biomarkers for disease progression. Advances in the diagnosis and management of these patients will require the establishment of multidisciplinary centers of excellence staffed by experts in this disease.

Storage pool diseases illuminate platelet dense granule biogenesis

Platelet dense granules (DGs) are membrane bound compartments that store polyphosphate and small molecules such as ADP, ATP, Ca²⁺, and serotonin. The release of DG contents plays a central role in platelet aggregation to form a hemostatic plug. Accordingly, congenital deficiencies in the biogenesis of platelet DGs underlie human genetic disorders that cause storage pool disease and manifest with prolonged bleeding. DGs belong to a family of lysosome-related organelles, which also includes melanosomes, the compartments where the melanin pigments are synthesized. These organelles share several characteristics including an acidic lumen and, at least in part, the molecular machinery involved in their biogenesis. As a result, many genes affect both DG and melanosome biogenesis and the corresponding patients present not only with bleeding but also with oculocutaneous albinism. The identification and characterization of such genes has been instrumental in dissecting the pathways responsible for organelle biogenesis. Because the study of melanosome biogenesis has advanced more rapidly, this knowledge has been extrapolated to explain how DGs are produced. However, some progress has recently been made in studying platelet DG biogenesis directly in megakaryocytes and megakaryocytoid cells. DGs originate from an endosomal intermediate compartment, the multivesicular body. Maturation and differentiation into a DG begins when newly synthesized DG-specific proteins are delivered from early/recycling endosomal compartments. The machinery that orchestrates this vesicular trafficking is composed of a combination of both ubiquitous and cell type-specific proteins. Here, we review the current knowledge on DG biogenesis. In particular, we focus on the individual human and murine genes encoding the molecular machinery involved in this process and how their deficiencies result in disease.

Hermansky-Pudlak Syndrome

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder that is associated with oculocutaneous albinism, bleeding diatheses, granulomatous colitis, and highly penetrant pulmonary fibrosis in some subtypes, including HPS-1, HPS-2, and HPS-4. HPS pulmonary fibrosis shows many of the clinical, radiologic, and histologic features found in idiopathic pulmonary fibrosis, but occurs at a younger age. Despite knowledge of the underlying genetic defects, there are currently no definitive therapeutic or preventive approaches for HPS pulmonary fibrosis other than lung transplant.

Inherited platelet disorders: toward DNA-based diagnosis

Variations in platelet number, volume, and function are largely genetically controlled, and many loci associated with platelet traits have been identified by genome-wide association studies (GWASs).(1) The genome also contains a large number of rare variants, of which a tiny fraction underlies the inherited diseases of humans. Research over the last 3 decades has led to the discovery of 51 genes harboring variants responsible for inherited platelet disorders (IPDs). However, the majority of patients with an IPD still do not receive a molecular diagnosis. Alongside the scientific interest, molecular or genetic diagnosis is important for patients. There is increasing recognition that a number of IPDs are associated with severe pathologies, including an increased risk of malignancy, and a definitive diagnosis can inform prognosis and care. In this review, we give an overview of these disorders grouped according to their effect on platelet biology and their clinical characteristics. We also discuss the challenge of identifying candidate genes and causal variants therein, how IPDs have been historically diagnosed, and how this is changing with the introduction of high-throughput sequencing. Finally, we describe how integration of large genomic, epigenomic, and phenotypic datasets, including whole genome sequencing data, GWASs, epigenomic profiling, protein-protein interaction networks, and standardized clinical phenotype coding, will drive the discovery of novel mechanisms of disease in the near future to improve patient diagnosis and management.

The ophthalmic presentation of Hermansky-Pudlak syndrome 6

BACKGROUND

Hermansky-Pudlak syndrome (HPS) may present to the ophthalmologist with signs suggestive of oculocutaneous albinism. Consideration of HPS as a differential diagnosis is important due to its potential systemic complications. HPS6 is a rarely reported subtype.

METHODS

Three patients from two families underwent clinical examination, imaging and targeted systemic investigations. Electrophysiology with visual-evoked potentials (VEPs) was performed in both children of family 1. Whole exome sequencing (WES) was performed on the proband of family 1. Bidirectional Sanger sequencing of the single exon and intron-exon boundaries of HPS6 was performed on all affected patients and segregation confirmed in available relatives.

RESULTS

Two siblings presented in infancy with nystagmus and reduced vision. They were initially diagnosed with isolated foveal hypoplasia with no aberrant chiasmal misrouting on VEPs. WES performed in the proband when 10 years of age identified a novel homozygous missense variant in HPS6 and further questioning elicited a history of nose bleeds and mild bruising. Segregation supported causality of this variant in the affected younger sibling. In the third unrelated patient, an initial diagnosis of ocular albinism was made at 3 months with HPS only diagnosed at 26 years. Biallelic, truncating mutations in HPS6 were identified by candidate Sanger sequencing and included a novel variant. Abnormal platelet function consistent with HPS was confirmed in all patients.

CONCLUSIONS

The diagnosis of HPS in all patients was delayed due to a mild systemic phenotype. Next-generation sequencing can aid diagnosis of syndromic conditions with important consequences for preventing morbidity.

Hermansky-Pudlak syndrome. Overview of clinical and molecular features and case report of a new HPS-1 variant

Hermansky-Pudlak syndrome (HPS) is a rare, autosomal recessive disorder affecting lysosome-related organelles (LRO), including dense platelet granules. HPS causes oculocutaneous hypopigmentation, bleeding diathesis and granulomatous colitis or pulmonary fibrosis. To date, there is no curative treatment and the clinical management depends on the severity of symptoms. A prompt diagnosis of HPS patients could improve their quality of life and clinical management. However, the absence of a specific platelet function test, the wide molecular heterogeneity, and the lack of phenotype-genotype correlations hamper the rapid diagnosis. Nine subtypes of HPS have been identified as a result of mutations in nine genes that codify for proteins involved in formation and shuttle of the LRO. The molecular characterization of patients and knowledge derived from animal models of HPS contribute to the understanding of biogenesis and function of the LRO. This paper describes a patient with a novel homozygous nonsense mutation causing HPS and provides a review of the literature focusing on recent advances in the molecular characterization and physiopathology of HPS.

Ocular Findings in Patients with the Hermansky-Pudlak Syndrome (Types 1 and 3)

PURPOSE

To describe and compare ocular findings in patients with Hermansky-Pudlak syndrome (HPS) type 1 and 3.

METHODS

This is a retrospective case series of 64 patients with HPS from 1999 to 2009 evaluated at an outpatient private ophthalmologic clinic. Patients underwent genetic analysis of selected albinism (Tyrosine and P gene) and HPS genes (HPS-1 and HPS-3) by screening for common mutations and exon sequencing with DNA screening. Descriptive and non-parametric statistical analyses were carried out.

RESULTS

Nearly 70% of the patients were homozygous for common Puerto Rican mutations leading to the HPS1 gene (16-BP DUP, 53.6%), while 30% had the 3904-BP DEL HPS3 gene mutation. Best corrected visual acuity (BCVA) was poorer in patients with type 1 HPS than in patients with type 3 HPS (p < 0.001), esotropia was more common among type 1 HPS patients (p < 0.018), while exotropia was more common among patients with type 3 HPS. Total iris transillumination was more common in patients with type 1 HPS and minimal iris transillumination in patients with type 3 HPS (p < 0.001). The maculae were translucent in patients with type 1 HPS, while patients with type 3 HPS had opaque maculae (p < 0.001).

CONCLUSIONS

Patients with type 1 HPS had poorer BCVA, increased incidence of esotropia, lighter iris and macular appearance. In contrast, patients with type 3 HPS had more exotropia. In addition, to our knowledge this is the largest series type 3 HPS ever reported.

Hypopigmentation in Hermansky-Pudlak syndrome

Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism, bleeding tendency, and ceroid deposition which often leads to death in midlife. Currently, nine genes have been identified as causative for HPS in humans. Hypopigmentation is the prominent feature of HPS, attributable to the disrupted biogenesis of melanosome, a member of the lysosome-related organelle (LRO) family. Current understanding of the cargo transporting mechanisms into the melanosomes expands our knowledge of the pathogenesis of hypopigmentation in HPS patients.

Caenorhabditis elegans HOPS and CCZ-1 mediate trafficking to lysosome-related organelles independently of RAB-7 and SAND-1

As early endosomes mature, the SAND-1/CCZ-1 complex acts as a guanine nucleotide exchange factor (GEF) for RAB-7 to promote the activity of its effector, HOPS, which facilitates late endosome-lysosome fusion and the consumption of AP-3-containing vesicles. We show that CCZ-1 and the HOPS complex are essential for the biogenesis of gut granules, cell type-specific, lysosome-related organelles (LROs) that coexist with conventional lysosomes in Caenorhabditis elegans intestinal cells. The HOPS subunit VPS-18 promotes the trafficking of gut granule proteins away from lysosomes and functions downstream of or in parallel to the AP-3 adaptor. CCZ-1 also acts independently of AP-3, and ccz-1 mutants mistraffic gut granule proteins. Our results indicate that SAND-1 does not participate in the formation of gut granules. In the absence of RAB-7 activity, gut granules are generated; however, their size and protein composition are subtly altered. These observations suggest that CCZ-1 acts in partnership with a protein other than SAND-1 as a GEF for an alternate Rab to promote gut granule biogenesis. Point mutations in GLO-1, a Rab32/38-related protein, predicted to increase spontaneous guanine nucleotide exchange, specifically suppress the loss of gut granules by ccz-1 and glo-3 mutants. GLO-3 is known to be required for gut granule formation and has homology to SAND-1/Mon1-related proteins, suggesting that CCZ-1 functions with GLO-3 upstream of the GLO-1 Rab, possibly as a GLO-1 GEF. These results support LRO formation occurring via processes similar to conventional lysosome biogenesis, albeit with key molecular differences.

An autopsy case of Hermansky-Pudlak syndrome: a case report and review of the literature on treatment

Hermansky-Pudlak syndrome (HPS) is a rare genetic disorder, the most common complication of which influencing the prognosis is pulmonary fibrosis. In the present report, we describe an autopsy case of a Japanese woman with HPS. The patient was diagnosed at 50 years of age based on the presence of oculocutaneous albinism, hemorrhagic diathesis, ceroid-lipofuscin accumulation and pulmonary fibrosis. Although systemic steroids, immunosuppressants and pirfenidone were administered for pulmonary involvement, she died from respiratory failure two years later. Obtaining an early diagnosis and taking into consideration the need for lung transplantation is necessary in order to improve the prognosis of HPS. We herein report this very rare Japanese case of HPS with a review of the treatment approaches for HPS complicated with pulmonary fibrosis.

Increasing the complexity: new genes and new types of albinism

Albinism is a rare genetic condition globally characterized by a number of specific deficits in the visual system, resulting in poor vision, in association with a variable hypopigmentation phenotype. This lack or reduction in pigment might affect the eyes, skin, and hair (oculocutaneous albinism, OCA), or only the eyes (ocular albinism, OA). In addition, there are several syndromic forms of albinism (e.g. Hermansky-Pudlak and Chediak-Higashi syndromes, HPS and CHS, respectively) in which the described hypopigmented and visual phenotypes coexist with more severe pathological alterations. Recently, a locus has been mapped to the 4q24 human chromosomal region and thus represents an additional genetic cause of OCA, termed OCA5, while the gene is eventually identified. In addition, two new genes have been identified as causing OCA when mutated: SLC24A5 and C10orf11, and hence designated as OCA6 and OCA7, respectively. This consensus review, involving all laboratories that have reported these new genes, aims to update and agree upon the current gene nomenclature and types of albinism, while providing additional insights from the function of these new genes in pigment cells.

Pathogenesis of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fibrosing interstitial lung disease associated with aging that is characterized by the histopathological pattern of usual interstitial pneumonia. Although an understanding of the pathogenesis of IPF is incomplete, recent advances delineating specific clinical and pathologic features of IPF have led to better definition of the molecular pathways that are pathologically activated in the disease. In this review we highlight several of these advances, with a focus on genetic predisposition to IPF and how genetic changes, which occur primarily in epithelial cells, lead to activation of profibrotic pathways in epithelial cells. We then discuss the pathologic changes within IPF fibroblasts and the extracellular matrix, and we conclude with a summary of how these profibrotic pathways may be interrelated.

snow white, a zebrafish model of Hermansky-Pudlak Syndrome type 5

Hermansky-Pudlak Syndrome (HPS) is a set of genetically heterogeneous diseases caused by mutations in one of nine known HPS genes. HPS patients display oculocutaneous hypopigmentation and bleeding diathesis and, depending on the disease subtype, pulmonary fibrosis, congenital nystagmus, reduced visual acuity, and platelet aggregation deficiency. Mouse models for all known HPS subtypes have contributed greatly to our understanding of the disease, but many of the molecular and cellular mechanisms underlying HPS remain unknown. Here, we characterize ocular defects in the zebrafish (Danio rerio) mutant snow white (snw), which possesses a recessive, missense mutation in hps5 (hps5I76N). Melanosome biogenesis is disrupted in snw/hps5 mutants, resulting in hypopigmentation, a significant decrease in the number, size, and maturity of melanosomes, and the presence of ectopic multi-melanosome clusters throughout the mutant retina and choroid. snw/hps5I76N is the first Hps5 mutation identified within the N-terminal WD40 repeat protein-protein binding domain. Through in vitro coexpression assays, we demonstrate that Hps5I76N retains the ability to bind its protein complex partners, Hps3 and Hps6. Furthermore, while Hps5 and Hps6 stabilize each other's expression, this stabilization is disrupted by Hps5I76N. The snw/hps5I76N mutant provides a valuable resource for structure-function analyses of Hps5 and enables further elucidation of the molecular and cellular mechanisms underlying HPS.