Paired melanotic and achromic macules in a case of phacomatosis pigmentovascularis: A further example of twin spotting?
✍ Scribed by de las Heras, Elena; Boixeda, Juan Pablo; Ledo, Antonio; Happle, Rudolf
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 603 KB
- Volume
- 70
- Category
- Article
- ISSN
- 0148-7299
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✦ Synopsis
Phacomatosis pigmentovascularis (PPV) comprises a telangiectatic nevus and a flat pigmentary nevus arranged in more or less extensive patches. To explain this phenotype, the concept of nonallelic twin spotting was proposed [Happle and Steijlen, 1989]. Twin spots are paired patches of mutant tissue that differ from each other and from the background tissue [Whitehouse, 1982].
In an organism heterozygous for two different recessive mutations located on the same chromosome, the event of somatic recombination may result in two homozygous daughter cells, giving rise to different mutant spots [Stern, 1936;Harrison and Carpenter, 1977;Happle et al., 1990]. According to this concept, PPV includes a third birthmark in the form of nevus anemicus [Ortonne et al., 1978;Hasegawa and Yasuhara, 1985;Hidano and Arai, 1987]. A nevus anemicus can be regarded as a minus counterpart due to allelism at the locus responsible for the pigmentary nevus. Here we report on an unusual case suggesting twin spotting due to allelism at this locus.
An 8-year-old girl was referred to our Department of Dermatology because of cutaneous vascular and pigmentary abnormalities. She had suffered from recurrent episodes of bronchopneumonia since birth. The cutaneous anomalies had first been noted in early childhood. No other relatives had similar lesions.
Physical examination showed a telangiectatic nevus involving her right cheek, as well as a light brown patch localized partly on the right cheek and extending to the right side of the neck (Figs. 1,2). In addition, a triangular hypopigmented patch was present on the right side of the upper back (Fig. 3). On diascopic pressure, the lesion could be distinguished from the blanched surrounding skin, excluding the differential diagnosis of nevus anemicus. Further checkup, including neurological and ophthalmological examination, did not show any additional anomalies. This unusual case can be taken as yet another clue in the understanding of the origin of PPV. If it is true that the two vascular components observed in this phenotype are caused by allelic mutation [Happle, 1991], one may infer that a similar phenomenon should sometimes occur at the neighboring locus responsible for the pigmentary component. In this way, the present case would represent a ''missing link'' in our line of thought, explaining PPV as a twin spot phenomenon.
The concept of twin spotting as a genetic basis of PPV