Electron Microscopy of Melanocytes in Human Piebaldism*

Cellular and ultrastructural characterization of the grey-morph phenotype in southern right whales (Eubalaena australis)

Southern right whales (SRWs, Eubalena australis) are polymorphic for an X-linked pigmentation pattern known as grey morphism. Most SRWs have completely black skin with white patches on their bellies and occasionally on their backs; these patches remain white as the whale ages. Grey morphs (previously referred to as partial albinos) appear mostly white at birth, with a splattering of rounded black marks; but as the whales age, the white skin gradually changes to a brownish grey color. The cellular and developmental bases of grey morphism are not understood. Here we describe cellular and ultrastructural features of grey-morph skin in relation to that of normal, wild-type skin. Melanocytes were identified histologically and counted, and melanosomes were measured using transmission electron microscopy. Grey-morph skin had fewer melanocytes when compared to wild-type skin, suggesting reduced melanocyte survival, migration, or proliferation in these whales. Grey-morph melanocytes had smaller melanosomes relative to wild-type skin, normal transport of melanosomes to surrounding keratinocytes, and normal localization of melanin granules above the keratinocyte nuclei. These findings indicate that SRW grey-morph pigmentation patterns are caused by reduced numbers of melanocytes in the skin, as well as by reduced amounts of melanin production and/or reduced sizes of mature melanosomes. Grey morphism is distinct from piebaldism and albinism found in other species, which are genetic pigmentation conditions resulting from the local absence of melanocytes, or the inability to synthesize melanin, respectively.

In vivo and in vitro evidence for epidermal H2O2-mediated oxidative stress in piebaldism

Piebaldism is characterised by the absence of pigment in patches on the skin, usually present at birth. Mutations in the kit gene are documented. Clinically this disorder can mimic vitiligo. Here, we show for the first time the presence of oxidised pteridine-induced fluorescence in association with H2O2-mediated stress in piebald patches employing Wood's light and in vivo FT-Raman spectroscopy. In situ immunofluorescence data revealed low catalase and methionine sulphoxide reductase A (MSRA) levels whereas thioredoxin reductase and methionine sulphoxide reductase B (MSRB) are not affected. We also show low superoxide dismutase levels in these patients. The presence of thioredoxin reductase provides capacity to reduce H2O2, a mechanism which is absent in vitiligo. Importantly, this enzyme reduces biopterin back to the functioning cofactor 6-tetrahydrobiopterin. The absence of MSRA indicates deficient methionine sulphoxide repair in the cytosol, meanwhile the presence of MSRB is helpful to protect the nucleus. Taken together, we have identified H2O2-mediated stress in piebald skin with distinct differences to vitiligo.

Expression of the c-kit receptor in hypomelanosis: a comparative study between piebaldism, naevus depigmentosus and vitiligo

In order to investigate possible alterations in c-kit protein expression on epidermal melanocytes in different hypopigmentary disorders, we have examined skin specimens from one patient with piebaldism, one patient with naevus depigmentosus, and five patients with vitiligo. Cryosections were examined by immunohistochemistry using monoclonal antibodies against the c-kit protein (YB5.B8) and melanosomes (TA99). In piebaldism, hypomelanotic epidermis contained only a few TA99-positive epidermal melanocytes and no detectable c-kit protein, whereas in naevus depigmentosus the expression of c-kit protein was strong, and TA99 immunoreactivity was faint. In vitiligo lesions, no epidermal immunoreactivity for melanosomes or c-kit protein was found. Normally pigmented skin of all patients showed immunoreactivity of epidermal melanocytes for both c-kit protein and melanosomes. Different hypomelanotic lesions can thus be differentiated by absent melanocyte c-kit protein and low or no expression of melanosomal marker in piebaldism, normal c-kit but low melanosome expression in naevus depigmentosus, and the absence of all melanocyte markers in vitiligo.

Inhibition of proliferation of human melanocytes by a KIT antisense oligodeoxynucleotide: implications for human piebaldism and mouse dominant white spotting (W)

KIT constitutes the cell surface transmembrane receptor protein tyrosine kinase for a growth factor variously termed steel factor (SLF), stem cell factor, mast cell growth factor, or Kit ligand. Inherited mutations of the KIT gene result in piebaldism in humans and dominant white spotting (W) in mice. Patches of hypopigmented skin and hair in these disorders represent regions lacking in melanocytes, the result of defective melanoblast differentiation, migration, proliferation, or survival during embryonic development. Here we show that incubation of normal human melanocytes with a KIT antisense oligodeoxynucleotide greatly inhibits cell proliferation in culture, whereas incubation with a KIT sense oligodeoxynucleotide has no effect. The KIT oligodeoxynucleotides also had little or no effect on cell survival.

Ultrastructural study of two patients with both piebaldism and neurofibromatosis 1

Piebaldism was associated with neurofibromatosis 1 (NF-1) in two patients, an association not previously reported. Dopa staining (tyrosinase) and electron microscopy were performed: no melanocytes or melanosomes were found in hypomelanotic skin of patient 2 and in the white forelock skin of patient 1; in patient 2, normal melanocytes and melanosomes were present in the white forelock epidermis but absent from the cortex, cuticles, and inner root sheath of the white forelock hair. Because these structures receive melanosomes from melanocytes in the hair bulb, it was assumed that there were no melanocytes in the hair matrix. Melanocytes and melanosomes were normal by ultrastructural criteria and in terms of their distribution in a normally pigmented macule within a hypomelanotic patch of patient 2. These and earlier report findings led to three conclusions: subtypes of piebaldism exist, including our patients showing a combination of piebaldism and NF-1; the most commonly reported subtype has no melanocytes in the white forelock and hypomelanotic skin, although microscopic islands of melanocytes may exist within hypomelanotic skin; and the ultrastructure of white forelock skin and hair of patient 2 is consistent with a mouse model of piebaldism, in which the hair follicle has no active melanocytes, but the interfollicular epidermis is normally melanized.

Novel mutations of the KIT (mast/stem cell growth factor receptor) proto-oncogene in human piebaldism

Piebaldism is an autosomal dominant genetic disorder of pigmentation characterized by congenital patches of white skin and hair that lack melanocytes. Piebaldism results from mutations of the KIT proto-oncogene, which encodes the cellular receptor transmembrane tyrosine kinase for mast/stem cell growth factor. Here we describe two novel KIT mutations associated with human piebaldism. These amino acid substitutions, located in the most highly conserved sections of the KIT kinase domain, would be expected to dominant-negatively inhibit KIT-dependent signal transduction, resulting in aberrant melanocyte proliferation or migration during embryologic development.

Deletion of the KIT and PDGFRA genes in a patient with piebaldism

We have previously shown that human piebaldism results from mutations of the KIT gene, which encodes the receptor for the mast/stem cell growth factor and is located in chromosome segment 4q12. Using DNA of a patient with piebaldism, mental retardation, and multiple congenital anomalies associated with a 46,XY,del(4) (q12q21.1) karyotype, we carried out quantitative Southern blot hybridization analyses of the KIT gene and the adjacent PDGFRA (platelet-derived growth factor receptor alpha subunit) genes. The patient was hemizygous for both the KIT and PDGFRA genes, indicating that both of these genes are included within the deleted region. Therefore, deletion of the KIT and PDGFRA genes may account for the piebald phenotype in this patient.

Disorders of hypopigmentation in children

The most common disorders of hypopigmentation in children are pityriasis alba, vitiligo, nevus depigmentosus, and tinea versicolor. Pityriasis alba usually presents as ill defined, scaly patches of hypomelanosis on the cheeks of children with an atopic diathesis. The face is also a favored site for vitiligo, but the distribution is periorificial, and the pigment loss is complete because of a destruction of melanocytes. Vitiligo is an acquired, progressive disorder in contrast to nevus depigmentosus, which is a stable, congenital leukoderma. The localized form of nevus depigmentosus must be distinguished from an ash leaf spot, the earliest cutaneous manifestation of tuberous sclerosis, whereas the systematized form may be confused with hypomelanosis of Ito, another neurocutaneous disorder. The lesions of tinea versicolor favor the upper trunk of adolescents, and potassium hydroxide examination of the associated scale reveals hyphal and yeast forms of P. orbiculare. Any inflammatory process in the skin such as dermatitis or psoriasis can resolve with areas of hypopigmentation.

Congenital dyschromia with erythrocyte, platelet, and tryptophan metabolism abnormalities

The case of a female child with a unique generalized congenital dyschromia is reported. She had hypopimented skin, with hypomelanosis and hypomelanocytosis, and many pigmented macules, which consisted of epidermal and dermal hypermelanosis without hypermelanocytosis. Biochemical investigations revealed normal catecholamine metabolism but abnormal tryptophan metabolism, including a decrease in blood serotonin and melatonin. A slight platelet storage pool disease was demonstrated, and a recurrent megaloblastic folate-related anemia occurred. The possible relationship between the pigmentary disease and the biochemical abnormalities is discussed. We suggest that this case represents a previously undescribed association of dyschromia, erythrocyte, platelet, and tryptophan metabolism abnormalities.

Biology of hypopigmentation

A review of the basics of pigment cell biology is followed by a discussion of the characteristics of several disorders of hypopigmentation. By determining such features as inheritance pattern, time of onset (congenital, childhood, adulthood), natural history (stable vs progressive), type of pigment loss (diffuse or circumscribed), distribution of lesions (generalized vs localized), degree of pigment loss (incomplete or complete), number of melanocytes, if any, in biopsy specimens of affected areas, type of melanocytic dysfunction, and associated inflammation or infection, one can classify the disorders of hypopigmentation. The proposed pathophysiology for each disorder of hypomelanosis is presented.

Pigmentary correction of piebaldism by autografts. I. Procedures and clinical findings

Full-thickness and epidermal autografts of normally pigmented skin were transplanted within hypopigmented areas in each of two patients with piebaldism. Full-thickness punch grafts 2 to 4 mm in size retained their pigmentation (donor dominance) and within 4 months pigment was found to have spread around them. Within a year, melanization covered roughly triple the diameter of the grafts (or 9 times their areas) and then came to a standstill. Epidermal grafts (about 12 mm in diameter) healed with no visible scars at either donor or recipient sites. These grafts, too, retained their pigmentation, but no pigment was seen to spread from them in 8 months of observation. Controls of hypopigmented, full-thickness autografts placed into comparable hypopigmented areas showed either no change or but slight pigmentation along the rim of the graft and no spread of pigment.

Expansion and contraction of hypomelanotic areas in human piebaldism

A case of human piebaldism with white forelock is presented, with emphasis on the unusual aspect of expansion and diminution of the hypomelanotic areas. Possible mechanisms of piebaldism and of changes in the hypomelanotic areas are discussed.

Fine structure and x-ray microanalysis of melanosomes in pigmented nevi and melanomas

Further finestructural characteristics of melanosomes in pigmented nevi and melanomas are described. The differences in the calcium, iron and surphur content of melanosomes derived from melanocytes, nevocytes and malignant melanoma cells are pointed out.

Congenital circumscribed hypomelanosis: a characterization based on electron microscopic study of tuberous sclerosis, nevus depigmentosus, and piebaldism

Subcellular defects of hypomelanosis in tuberous sclerosis (TS) (28 subjects) were compared by light and electron microscopy with oThere forms of congenital circumscribed hypomelanosis that occur in nevus depigmentosus (ND) (8 subjects) and in piebaldism (PB) (4 subjects), respectively. On the light microscopic level in both TS and ND, the population density of functioning melanocytes was normal but each perikaryon was small, and dopa activity was decreased. On the ultrastructural level, the hypomelanotic skin and hair of TS were associated with a decrease in the synthesis, melanization, and size of melanosomes; the decrease in the size of melanosomes resulted in the aggregation of melanosomes (i.e., a melanosome complex) in the keratinocytes in all the specimens examined. In ND, ther were no obvious changes in the size and melanocytes. the hypomelanosis of ND is related to the decreased synthesis and also, perhaps, abnormal transfer of melanosomes. In PB the hypomelanosis of the skin and hair results from the absence of functional melanocytes. The hypermelanotic areas of PB, however, characteristically contain melanocytes that synthesize abnormal (sperical and granular) as well as normal (ellipsoidal and lamellar) melanosomes.

Mast cells in the epidermis of piebaldism

The depigmented lesion in a case of piebaldism (partial albinism) was examined by electron microscopy. In the epidermis melanocytes were absent and the number of Langerhans cells was increased. In addition several mast cells were found in the epidermis.