ARTICLE
In 1993, the phylloid pattern was delineated as a distinct form of pigmentary
mosaicism characterized by an arrangement of pigmentary lesions reminiscent
of a floral ornament or art nouveau painting (Greek phyllon = leaf, eidos
= form) [1]. This pattern is composed of various elements such as round
or oval patches, lesions resembling the asymmetrical leaves of a begonia,
large pear-shaped areas or oblong macules (Fig.
1). Most of the reported cases deal with hypomelanosis, and in
6 of these patients cytogenetic findings were described. It is the purpose
of this article to draw attention to an apparent causal relationship between
phylloid hypomelanosis and mosaic trisomy 13.
Materials and methods
Four cases of phylloid hypomelanosis with documentation of cytogenetic
findings were collected from the literature [2-4]. Additional information
on a case reported by Ohashi et al. [2] was obtained by correspondence
with Dr. Kenji Naritomi, Okinawa, Japan. Two additional cases [5, 6] will
soon be published and are included in this review.
Results
Cytogenetic findings as documented in these 6 cases are reviewed in
Table 1. All patients
were girls, and all of them had associated CNS defects as well as other
extracutaneous anomalies. With the exception of one case associated with
mosaic trisomy 14, cytogenetic analysis showed aberrations involving chromosome
13. In three of these cases, karyotyping of blood lymphocytes revealed
a 46, XX/47, XX, +13 or 46, XX/47, XX, +der (13) mosaic, whereas in the
other two cases a chromosome constitution 46, XX, t(13;13) was noted.
In fibroblast cultures, Ohashi et al. [2] found the abnormal karyotype
in 97% of cells derived from light skin as compared to 56% of cells derived
from dark skin. By contrast, Pillay et al. constantly found a 46,
XX, t(13;13) karyotype in skin fibroblasts from both dark and light skin,
without demonstration of mosaicism. Ribeiro-Noce et al. [5] examined
skin fibroblasts derived from two skin samples and found a karyotype 46
XX, t(13q;13q) present in 14% of cells, as well as absence of a chromosome
13 in two other cell lines. No normal karyotype was found. In this case
it was not possible to assign any of the aberrant karyotypes to a specific
area of pigmentary disturbance. In a patient showing both hypo- and hyperpigmented
phylloid lesions, Schepis et al. [6] found trisomy 13 in 25% of
skin fibroblasts.
Discussion
Complete or partial trisomy 13 was reported in 5 out of 6 cases of phylloid
hypomelanosis in which a cytogenetic analysis was performed. Mosaic trisomy
13 was demonstrated in skin fibroblasts derived from 4 of these patients
[2, 3, 5, 6]. In the 5th case [4] the phylloid hypomelanosis probably
reflected a mosaic of the melanocyte system involving chromosome 13 because
analysis of blood lymphocytes and skin fibroblasts revealed a translocation
of chromosome 13 on 13. Although phylloid hypomelanosis may sometimes
reflect other forms of mosaicism, the cases reported so far indicate that
this type of skin disorder is not caused by randomly distributed chromosomal
anomalies but preponderantly originates from mosaic trisomy 13.
CONCLUSION
In conclusion, phylloid hypomelanosis is strikingly different from hypomelanosis
of Ito, a congenital pigmentary disorder following the lines of Blaschko
that has been found to represent a cutaneous symptom of many different
chromosomal abnormalities [7-10]. Conversely, the phylloid type of hypomelanosis
appears to herald rather constantly a mosaic state involving chromosome
13. Future case reports may help to elucidate further this causal relationship.
Article accepted on 26/7/00
REFERENCES
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