Giant and “Granular Melanosomes” in Leopard Syndrome: An Ultrastructural Study

Abstract

Electron microscopy of lentigines was performed to study the pigmentation abnormality in two children with LEOPARD syndrome. Giant melanosomes similar to those seen in café-au-lait spots of neurofibromatosis and nevus spilus were found in a lentigine from one of our cases. Our results show that "spherical granular melanosomes" described in neurofibromatosis, are lysosomal-like structures associated with the development of complex melanin granules. Our study also demonstrates that immature melanosomes are present in some keratinocytes of LEOPARD syndrome. This finding is in contrast to the prevailing concept that only mature melanosomes are transferred to keratinocytes. The occurrence of individual melanosomes of normal size and shape in keratinocytes of skin in whites with LEOPARD syndrome, suggests that neither the size of melanosomes, nor the racial differences are the factors determining the distribution of melanosomes in keratinocytes.

Becker’s Melanosis: an Ultrastructural Study

“…These authors suggested that the distribution pattern of melanosomes was dependent upon the size of melanosomes irrespective of race. The presence of individual melanosomes smaller than 0.8 mm in kératinocytes in the present investigation and in the kératinocytes of the lentigines in LEOPARD syndrome [3] suggests that the distribution of melanosomes is not necessarily dependent on race or size. Our findings are further supported by the obser vations of Takahashi [17], who found singly dispersed melanosomes in kératinocytes of nevus spilus but melanosomal complexes in café au lait spots, even though there was no difference in the size of melanosomes.…”

“…It is possible that melanosomes are transferred into kératinocytes at a speed much greater than their ability to aggregate them in complexes in the hypermelanotic state of Becker's melanosis as seen here, lentigines of LEO PARD syndrome [3] and nevus spilus [17]. Takahashi [17] supposed that melanosomal complexes in café au lait spots were seen because melanosomes were produced more abundantly.…”

“…Giant melanosomes were not seen in the previous electron microscopic slides, on Becker's melanosis [8,9], Jimbow et al [11] first described giant melanosomes in the café au lait spots of neurofibromato sis by electron microscopy. Since then, giant melanosomes have been described in nevus spilus [12], nevoid pigmentation [6], and rarely in normal skin [ 13], They havealsobeen seen inLEOPA RD syndrome [3], eruptive nevi[7[, neurofibromatosis [17], and in skin adjacent to malignant melanoma [16]. The ultrastructure of giant melanosomes has been described earlier in detail [3], The significance of these melanosomes ist still not clear despite several reports.…”

“…Since then, giant melanosomes have been described in nevus spilus [12], nevoid pigmentation [6], and rarely in normal skin [ 13], They havealsobeen seen inLEOPA RD syndrome [3], eruptive nevi[7[, neurofibromatosis [17], and in skin adjacent to malignant melanoma [16]. The ultrastructure of giant melanosomes has been described earlier in detail [3], The significance of these melanosomes ist still not clear despite several reports. Hypermelanosis is one common denominator in all the conditions where giant melanosomes have been described.…”

Pigment Cell Biology and Its Relation to Disorders of Melanin Pigmentation

“…The melanization of the giant melanosomes is usually most pronounced at its centre. The significance of this alteration in melanosomal morphology is as yet unclear [22], Giant melanosomes occur frequently in naevus spilus [21] and in café au lait spots of neurofibromatosis [15], rarely in lentigines [1], naevus cell naevi and in normal skin [23]. When present, they can be easily detected by light microscopy ( fig.…”