Albinism

Endogenous DOPA inhibits melanoma through suppression of CHRM1 signaling

Melanoma risk is 30 times higher in people with lightly pigmented skin versus darkly pigmented skin. Using primary human melanocytes representing the full human skin pigment continuum and preclinical melanoma models, we show that cell-intrinsic differences between dark and light melanocytes regulate melanocyte proliferative capacity and susceptibility to malignant transformation, independent of melanin and ultraviolet exposure. These differences result from dihydroxyphenylalanine (DOPA), a melanin precursor synthesized at higher levels in melanocytes from darkly pigmented skin. We used both high-throughput pharmacologic and genetic in vivo CRISPR screens to determine that DOPA limits melanocyte and melanoma cell proliferation by inhibiting the muscarinic acetylcholine receptor M1 (CHRM1) signaling. Pharmacologic CHRM1 antagonism in melanoma leads to depletion of c-Myc and FOXM1, both of which are proliferation drivers associated with aggressive melanoma. In preclinical mouse melanoma models, pharmacologic inhibition of CHRM1 or FOXM1 inhibited tumor growth. CHRM1 and FOXM1 may be new therapeutic targets for melanoma.

Histidine residues at the copper-binding site in human tyrosinase are essential for its catalytic activities

Tyrosinase is a copper-binding enzyme involved in melanin biosynthesis. However, the detailed structure of human tyrosinase has not yet been solved, along with the identification of the key sites responsible for its catalytic activity. We used site-directed mutagenesis to identify the residues critical for the copper binding of human tyrosinase. Seven histidine mutants in the two copper-binding sites were generated, and catalytic activities were characterised. The tyrosine hydroxylase activities of the CuA site mutants were approximately 50% lower than those of the wild-type tyrosinase, while the dopa oxidation activities of the mutants were not significantly different from that of wild-type tyrosinase. By contrast, mutations at CuB significantly decreased both tyrosine hydroxylation and dopa oxidation activities, confirming that the catalytic sites for these two activities are at least partially distinct. These findings provide a useful resource for further structural determination and development of tyrosinase inhibitors in the cosmetic and pharmaceutical industries.

Coexistence of Hermansky-Pudlak syndrome and JAK2V617F-positive essential thrombocythemia

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder consisting of oculocutaneous albinism, platelet storage pool deficiency, and lysosomal accumulation of ceroid lipofuscin. The storage pool deficiency of HPS is associated with the lack of dense bodies in the platelets, resulting in impaired response in the secondary phase of aggregation. Patients with HPS have normal coagulation tests; however, their bleeding time is usually prolonged despite normal or increased platelet counts. Essential thrombocythemia (ET) is an uncommon condition, with an incidence of approximately 1.1 per 100,000/year, and it is the most common cause of primary thrombocytosis. JAK2^V617F positivity can be observed in approximately half of the patients with ET. Bleeding events in ET have usually been associated with acquired von Willebrand syndrome paradoxically occurring when the platelet counts are extremely high. We, herein, present a case with bleeding diathesis diagnosed as having both HPS and JAK2^V617F-positive ET.

Functional validation of the albinism-associated tyrosinase T373K SNP by CRISPR/Cas9-mediated homology-directed repair (HDR) in rabbits

Background

Oculocutaneous albinism (OCA) is a group of autosomal recessive disorders characterized by reduced melanin that are caused by mutations in the gene encoding tyrosinase (TYR), which is the rate-limiting enzyme in the production of the pigment melanin. Many studies or meta-analyses have suggested an association between the TYR T373K SNP and OCA1, but there is limited biochemical and genetic evidence to support this association.

Methods

We overexpressed TYR-WT and TYR-T373K mutants on HK293T cells and tested the changes of melanin production and tyrosinase activity. Then we generated TYR-K373T knock-in (KI) rabbits by microinjection of ssDNA and synthesized RNAs targeting C1118A using CRISPR/Cas9-HDR to observe the formation of melanin.

Findings

We demonstrated that the T373K mutation in TYR can reduce tyrosinase activity, leading to an absence of melanin synthesis at the cell-level. The gene-edited TYR-K373T rabbits exhibited rescued melanin production in hair follicles and irises, as inferred from the evident decrease in pigmentation in TYR-T373K rabbits, thus providing functional validation of the albinism-associated T373K SNP at the animal level.

Interpretation

Our study provides the first animal-level functional validation of the albinism-associated TYR K373T SNP in rabbits, and these results will facilitate gene therapy of OCA1 in pre-clinical settings in the future.

Fund

The National Key Research and Development Program of China Stem Cell and Translational Research, the Strategic Priority Research Program of the Chinese Academy of Sciences, the Guangdong Province Science and Technology Plan Project, and the Program for JLU Science and Technology Innovative Research Team.

Skin cancers among Albinos at a University teaching hospital in Northwestern Tanzania: a retrospective review of 64 cases

Background

Skin cancers are a major risk associated with albinism and are thought to be a major cause of death in African albinos. The challenges associated with the care of these patients are numerous and need to be addressed. The aim of this study was to outline the pattern and treatment outcome of skin cancers among albinos treated at our centre and to highlight challenges associated with the care of these patients and proffer solutions for improved outcome.

Methods

This was a retrospective study of all albinos with a histopathological diagnosis of skin cancer seen at Bugando Medical Centre from March 2001 to February 2010. Data collected were analyzed using descriptive statistics.

Results

A total of 64 patients were studied. The male to female ratio was 1.5:1. The median age of patients was 30 years. The median duration of illness at presentation was 24 months. The commonest reason for late presentation was financial problem. Head and the neck was the most frequent site afflicted in 46(71.8%) patients. Squamous cell carcinoma was the most common histopathological type in 75% of cases. Surgical operation was the commonest modality of treatment in 60 (93.8%) patients. Radiotherapy was given in 24(37.5%) patients. Twenty-seven (42.2%) of the patients did not complete their treatment due to lack of funds. Local recurrence following surgical treatment was recorded in 6 (30.0%) patients. Only thirty-seven (61.7%) patients were available for follow-up at 6–12 months and the remaining patients were lost to follow-up.

Conclusions

Skin cancers are the most common cancers among albinos in our environment. Albinism and exposure to ultraviolet light appears to be the most important risk factor in the development of these cancers. Late presentation and failure to complete treatment due to financial difficulties and lack of radiotherapy services at our centre are major challenges in the care of these patients. Early institution of preventive measures, early presentation and treatment, and follow-up should be encouraged in this population for better outcome.

Albinism in Africa as a public health issue

BACKGROUND

Oculocutaneous albinism (OCA) is a genetically inherited autosomal recessive condition and OCA2, tyrosine-positive albinism, is the most prevalent type found throughout Africa. Due to the lack of melanin, people with albinism are more susceptible to the harmful effects of ultraviolet radiation exposure. This population must deal with issues such as photophobia, decreased visual acuity, extreme sun sensitivity and skin cancer. People with albinism also face social discrimination as a result of their difference in appearance. The World Health Organization is currently investigating the issues concerning this vulnerable population.

METHODS

Systematic electronic search of articles in PubMed concerning albinism in Africa. Furthermore, a World Health Organization (WHO) pilot survey of albinism was drafted in English, French and Portuguese, and distributed to African countries through WHO African Regional Offices (AFRO) in an attempt to gather further information on albinism.

RESULTS

Epidemiologic data on albinism, such as prevalence, were available for South Africa, Zimbabwe, Tanzania and Nigeria. Prevalences as high as 1 in 1,000 were reported for selected populations in Zimbabwe and other specific ethnic groups in Southern Africa. An overall estimate of albinism prevalences ranges from 1/5,000-1/15,000. In addition, both the literature review and the survey underscored the medical and social issues facing people with albinism.

CONCLUSION

The estimated prevalence of albinism suggests the existence of tens of thousands of people living with albinism in Africa. This finding reiterates the need for increased awareness of and public health interventions for albinism in order to better address the medical, psychological and social needs of this vulnerable population.

Oculocutaneous albinism

Oculocutaneous albinism represents a group of inherited skin disorders characterized by a generalized reduction of cutaneous, ocular and pilar pigmentation from the time of birth. Oculocutaneous albinism types 1 and 2 are the most common, but several other types have been described. A defect in the melanin synthesis pathway, resulting in reduced formation of melanin, is responsible for oculocutaneous albinism. Aetiology, clinical manifestations, diagnosis and management are discussed.

Hermansky-Pudlak syndrome: radiography and CT of the chest compared with pulmonary function tests and genetic studies

OBJECTIVE

The objective of our study was to describe the chest radiographic and high-resolution CT findings in patients with Hermansky-Pudlak syndrome and to correlate the radiologic findings with age, causative gene, and pulmonary function.

SUBJECTS AND METHODS

Sixty-seven patients with Hermansky-Pudlak syndrome underwent high-resolution CT of the chest. A scoring system based on the extent of pulmonary involvement and specific high-resolution CT findings was used, and the findings were compared with patient age and the results of pulmonary function and genetic studies. Fifty-eight (87%) of the 67 patients also underwent chest radiography. These radiographs were compared with the high-resolution CT scans.

RESULTS

High-resolution CT was more sensitive than chest radiography in evaluating the extent of pulmonary disease in patients with Hermansky-Pudlak syndrome. All patients with mild findings on high-resolution CT scans had normal findings on chest radiographs. Common chest radiographic findings included reticulonodular interstitial pattern, perihilar fibrosis, and pleural thickening. High-resolution CT showed septal thickening, ground-glass opacities, and peribronchovascular thickening. For patients with Hermansky-Pudlak syndrome who were 30 years old or younger, high-resolution CT findings were usually minimal. Among patients who were older than 30 years, the 34 patients with HPS1 mutations had a score of 1.38+/-0.18 (mean+/-standard error of the mean) on high-resolution CT. This score is significantly greater than the score for the 11 patients without HPS1 mutations (0.36 +/- 0.15) (p < 0.001). The score based on high-resolution CT findings inversely correlated with percentage of forced vital capacity and was useful in defining the progression of interstitial disease.

CONCLUSION

High-resolution CT provides a good radiologic monitor of disease status and progression in patients with Hermansky-Pudlak syndrome and correlates well with patient age, extent of pulmonary dysfunction, and genetic findings.

Mutations at critical N-glycosylation sites reduce tyrosinase activity by altering folding and quality control

Tyrosinase is a copper-containing enzyme that regulates melanin biosynthesis in mammals. Mutations at a single N-glycosylation sequon of tyrosinase have been reported to be responsible for oculocutaneous albinism type IA in humans, characterized by inactive tyrosinase and the total absence of pigmentation. To probe the role that each N-glycosylation site plays in the synthesis of biologically active tyrosinase, we analyzed the calnexin mediated folding of tyrosinase N-glycosylation mutants. We have determined that four of the six potential N-glycosylation sites, including that associated with albinism, are occupied. Analysis of the folding pathway and activity of 15 tyrosinase mutants lacking one or more of the occupied N-glycosylation sites shows that glycans at any two N-glycosylation sites are sufficient to interact with calnexin and give partial activity, but a specific pair of sites (Asn(86) and Asn(371)) is required for full activity. The mutants with less than two N-glycosylation sites do not interact with calnexin and show a complete absence of enzyme activity. Copper analysis of selected mutants suggests that the observed partial activity is due to two populations with differential copper content. By correlating the degree of folding with the activity of tyrosinase, we propose a local folding mechanism for tyrosinase that can explain the mechanism of inactivation of tyrosinase N-glycosylation mutants found in certain pigmentation disorders.

Genetic defects and clinical characteristics of patients with a form of oculocutaneous albinism (Hermansky-Pudlak syndrome)

BACKGROUND

Hermansky-Pudlak syndrome is characterized by oculocutaneous albinism, a storage-pool deficiency, and lysosomal accumulation of ceroid lipofuscin, which causes pulmonary fibrosis and granulomatous colitis in some cases. All identified affected patients in northwest Puerto Rico are homozygous for a 16-bp duplication in exon 15 of a recently cloned gene, HPS. We compared the clinical and laboratory characteristics of these patients with those of patients without the 16-bp duplication.

METHODS

Forty-nine patients -- 27 Puerto Ricans and 22 patients from the mainland United States who were not of Puerto Rican descent -- were given a diagnosis on the basis of albinism and the absence of platelet dense bodies. We used the polymerase chain reaction to determine which patients carried the 16-bp duplication.

RESULTS

Twenty-five of the Puerto Rican patients were homozygous for the 16-bp duplication, whereas none of the non-Puerto Rican patients carried this mutation. Like the patients without the duplication, the patients with the 16-bp duplication had a broad variation in pigmentation. Nine of 16 adults with the duplication, but none of the 10 without it, had a diffusing capacity for carbon monoxide that was less than 80 percent of the predicted value. High-resolution computed tomography in 12 patients with the 16-bp duplication revealed minimal fibrosis in 8, moderate fibrosis in 1, severe fibrosis in 1, and no fibrosis in 2. Computed tomography in eight patients without the duplication revealed minimal fibrosis in three and no fibrosis in the rest. Inflammatory bowel disease developed in eight patients (four in each group) between 3 and 25 years of age.

CONCLUSIONS

The 16-bp duplication in exon 15 of HPS, which we found only in Puerto Rican patients, is associated with a broad range of pigmentation and an increased risk of restrictive lung disease in adults.

Mutations of the tyrosinase gene in three Korean patients with type I oculocutaneous albinism

Oculocutaneous albinism (OCA) is an inherited disorder of the melanin pigmentary system, characterized by a decrease or an absence of melanin in the skin, hair, and eyes. Type I (tyrosinase-deficient) OCA results from mutations of the tyrosinase (TYR) gene encoding tyrosinase, the enzyme that catalyzes at least the first two steps of melanin biosynthesis. We have analyzed the TYR gene in three Korean patients with severe type I OCA. Two patients were compound heterozygotes for the Arg (CGG) to Gln (CAG) mutation at position 77 and a C insertion mutation at position 310. The other was a compound heterozygote for a C insertion mutation at position 310 and the Asp (GAT) to Asn (AAT) mutation at position 383. These mutations were easily detected by restriction enzyme digestion or by SSCP analysis. Such methods of mutation analysis thus provide a basis for a screening system for the TYR gene mutations in Korean patients with type I OCA.

Autosomal-recessive neural crest syndrome with albinism, black lock, cell migration disorder of the neurocytes of the gut, and deafness: ABCD syndrome

We report on a macrosomic newborn girl with albinism, a black lock at the right temporo-occipital region, and retinal depigmentation. Bilateral deafness was confirmed by brainstem auditory-evoked potentials. In addition, the infant had a severe defect of intestinal innervation. Biopsy showed aganglionosis of the large intestine, and total absence of neurocytes and nerve fibers in the small intestine, indicating a total lack of sympathetic and parasympathetic innervation. The infant died of intestinal dysfunction at 5 weeks. She was the 14th child of consanguineous Kurdish parents. Four sibs of our patient had the same syndrome and died a few days after birth. The other 9 sibs are well, with an unremarkable phenotype. A syndrome of albinism, black lock, deafness, and a total lack of intestinal neural innervation has not yet been reported. It represents a new neural crest syndrome with autosomal-recessive inheritance.

Actinic damage and skin cancer in albinos in northern Tanzania: findings in 164 patients enrolled in an outreach skin care program

Persons with albinism are particularly vulnerable to the deleterious effects of UV light on their skin. We obtained histories and performed skin examinations on 164 albino patients living in equatorial Africa to determine their sun exposure, sun protection, and sun damage. Many patients did not wear hats and most wore short-sleeved shirts. Except for four infants, all patients had sunburned skin. Actinic cheilitis, actinic keratoses, and skin cancers were detected in many patients. Sun protection methods will be important for prevention of skin damage in albino patients.

Mutations of the P gene in oculocutaneous albinism, ocular albinism, and Prader-Willi syndrome plus albinism

BACKGROUND

Type II (tyrosinase-positive) oculocutaneous albinism is an autosomal recessive disorder that has recently been mapped to chromosome segment 15q11-q13. The frequency of this disorder is greatly increased in patients with Prader-Willi or Angelman syndrome, both of which involve deletions of chromosome 15q. The P protein is a transmembrane polypeptide that may transport small molecules such as tyrosine, the precursor of melanin. The P gene is located in chromosome segment 15q11-q13.

METHODS

We studied the tyrosinase and P genes in three patients with type II oculocutaneous albinism, one of whom also had Prader-Willi syndrome, and in one patient with a milder syndrome known as autosomal recessive ocular albinism. Individual exons of these genes were amplified from the DNA of each patient by the polymerase chain reaction and screened for mutations by simultaneous analyses of single-stranded conformation polymorphisms and heteroduplexes and subsequent DNA sequencing.

RESULTS

Mutations of the P gene were identified in all four patients. These included one frame shift, three missense mutations that result in amino acid substitutions, and one mutation that affects RNA splicing. The patient with Prader-Willi syndrome plus albinism had a typical deletion of the paternal chromosome 15, rendering him hemizygous for a maternally inherited mutant allele of the P gene. The child with ocular albinism was heterozygous for two different mutations in the P gene.

CONCLUSIONS

Abnormalities of the P gene are associated with a wide range of clinical phenotypes, including type II oculocutaneous albinism, albinism associated with the Prader-Willi syndrome, and at least some cases of autosomal recessive ocular albinism.

Synergistic effect of storage pool deficient platelets and low plasma von Willebrand factor on the severity of the hemorrhagic diathesis in Hermansky-Pudlak syndrome

A study of 565 Puerto Rican patients with storage pool deficient (SPD) Hermansky-Pudlak syndrome (HPS) demonstrated that most HPS patients had minor bleeding episodes while others had repeated, severe hemorrhagic episodes requiring transfusion. The severity of bleeding in these latter patients could not be attributed to their SPD alone. As swine with SPD platelets and low von Willebrand factor antigen (vWF:Ag) have more severe hemorrhages than pigs with either defect alone, 146 albino patients and 46 normally pigmented patients were examined for their level of vWF:Ag. The risk of SPD HPS patients having severe, repeated bleeding episodes increased when vWF:Ag fell below 70 U/dL. Family studies indicated that low vWF:Ag levels were more frequently associated with O blood group than from a gene suppressing production or release of vWF1. HPS patients should be tested for vWF:Ag levels.

An ultrastructural study of melanocytes and melanosomes in the skin and hair bulbs of rufous albinos

We have examined hair bulb and skin melanocytes of rufous albinos from Southern Africa to further characterize this form of albinism. In the skin melanocytes we find both eumelanosomes and pheomelanosomes at various stages of melanization and, in addition, there appeared to be many aberrant incompletely melanized melanosomes. On average, rufous melanosomes are 30% smaller than normal black skin melanosomes. In the keratinocytes, the melanosomes are packaged into distinct aggregations, whereas in normal black skin, they occur singly. We suggest that the reddish skin color of these albinos is a consequence of an increase in the pheomelanin synthesis resulting in a raised pheomelanin/eumelanin ratio and that the aggregation of melanosomes results in a skin color slightly lighter than normal. In hair bulb melanocytes, only eumelanosomes were seen and these were mostly incompletely melanized. These findings correlate with our visual observations that the hair color of Southern African albinos is very pale (light brown or ginger). Based on our observations, we speculate on the possible cause of rufous albinism.

Dyschromatosis universalis with X-linked ocular albinism

A 10-year-old Chinese boy with the characteristic skin manifestations of dyschromatosis universalis is described. In addition, the patient had congenital nystagmus with poor visual acuity, and ophthalmological examination revealed foveal hypoplasia and albino-like fundi. Histopathology showed giant pigment granules in the skin. Based upon the finding of giant pigment granules in clinically normal skin of the patient's mother, the patient was diagnosed as a case of dyschromatosis universalis with X-linked ocular albinism. To the best of our knowledge, this is the first documented case of this combination.

Tyrosinase positive albinism with familial 46,XY,t(2;4) (q31.2;q31.22) balanced translocation

A subject with clinical and biochemical tyrosinase positive oculocutaneous albinism (OCA) also had a balanced translocation, 46,XY,t(2;4)(q31.2;q31.22). This observation provides evidence for a possible gene locus in the q31 region of chromosome 2 or 4.

The Yemenite deaf-blind hypopigmentation syndrome. A new oculo-dermato-auditory syndrome

We have seen a Yemenite sister and brother with cutaneous hypomelanotic and pigmented spots and patches, microcornea, coloboma, severe hearing loss and normal karyotypes. Histopathological examinations of the skin showed absent melanocytes in the depigmented areas; in the normal and hyperpigmented skin there was abundant melanotic pigment. Similar patients have not been described previously, but there are corresponding mutations in mice and rats.