title: Monozygotic twins discordant for phacomatosis pigmentovascularis: evidence for the concept of twin spotting.
abstract: The term phacomatosis pigmentovascularis (PPV) refers to the occurrence of vascular nevi with melanocytic or epidermal nevi. We report on monozygotic twins (MZTs) discordant for phacomatosis cesioflammea (PPV type II) providing evidence for the mechanism of twin spotting in the development of PPV. The affected twin had a nevus flammeus on the right arm and the right maxilla, and a pigmented area on the trunk in keeping with a persistent, aberrant Mongolian spot. The affected twin had bilateral ocular melanocytosis with abnormal scleral pigmentation, iris mamillations, increased pigmentation of the trabecular meshwork, and increased fundal pigmentation and secondary glaucoma. DNA testing confirmed monozygosity. This case of MZTs discordant for PPV supports the hypothesis that PPV results from mosaicism due to a post-zygotic mutational event and the concept of twin spotting.
authors.affiliation: Department of Ophthalmology, Royal Victoria Hospital, Belfast, Northern Ireland, UK.
authors.forename: Tanya
authors.initials: T
authors.lastname: Moutray
authors.forename: Maria
authors.initials: M
authors.lastname: Napier
authors.forename: Ayad
authors.initials: A
authors.lastname: Shafiq
authors.forename: Alan
authors.initials: A
authors.lastname: Fryer
authors.forename: Simon
authors.initials: S
authors.lastname: Rankin
authors.forename: Colin E
authors.initials: CE
authors.lastname: Willoughby
mesh_terms: D004200:Diseases in Twins / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D005123:Eye / Q000098:blood supply / Q000473:pathology; D005260:Female; D006801:Humans; D008548:Melanosis / Q000235:genetics / Q000473:pathology; D008957:Models, Genetic; D049328:Mongolian Spot / Q000235:genetics / Q000473:pathology; D009030:Mosaicism; D020752:Neurocutaneous Syndromes / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D010641:Phenotype; D010859:Pigmentation Disorders / Q000235:genetics / Q000473:pathology; D014430:Twins, Monozygotic; D054079:Vascular Malformations / Q000235:genetics / Q000473:pathology