Malformations and Genodermatoses
Numerous malformations also or exclusively affect the skin. Some of them are obvious and unmistakable, others are discreet, occurring at hidden localizations and are only discovered with the course of time. As can be seen from the example of aplasia cutis
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The original title “Malformations and Genodermatoses” is retained in the new edition, though this chapter is dedicated exclusively to malformations while genodermatoses are dealt with in the chapter “Genodermatoses II.”
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Aplasia Cutis Congenita
(Cordon 1767) Synonyms Aplasia cutis circumscripta, congenital absence of skin Definition The term is used for a group of rare disorders whose common characteristic is a congenital absence of skin in one or more circumscribed or extensive areas. In about 80% of cases, the aplasia cutis congenita (ACC) is located on the scalp. The depth ranges from superficial epidermal loss to bony defects. Smaller lesions may already have epithelialized in utero and appear as scarred areas at birth. When located on the scalp, underlying bone defects are seen in up to 15–20% of cases. Depth of involvement varies, and involvement of dural structures in particular can cause life-threatening complications. Moreover, ACC may be associated with other diverse abnormalities and syndromes (Eichenfield et al. 2014; Wobser and Hamm 2019). Epidemiology About 1–3 in 10,000 live births are affected. Etiopathogenesis The multitude of etiologies led to classification into nine groups taking into account cause, localization, and associated malformations (Frieden’s Classification, Table 1).
H. Hamm (*) · F. Ickrath Clinic and Policlinic for Dermatology, Venereology and Allergology, University Hospital Würzburg, Würzburg, Germany e-mail: [email protected]; [email protected] © Springer-Verlag GmbH Germany, part of Springer Nature 2020 G. Plewig et al. (eds.), Braun-Falco´s Dermatology, https://doi.org/10.1007/978-3-662-58713-3_56-1
Exogenous factors such as intrauterine trauma, detached amniotic adhesions, viral infections, and teratogens as well as endogenous causes such as vascular anomalies, genetic diseases, and chromosomal aberrations can be differentiated. In many cases of membranous ACC, incomplete or faulty closure of embryonic fusion lines or the neural tube is assumed, while the non-membranous form seems to have more vascular causes. The frequent occurrence at the vertex can at least partly be explained by the tight stretching of the skin during the rapid skull growth in the 10–15th week of pregnancy. Genetic causes of ACC are heterogeneous and mutations have been found in genes previously not known to regulate skin morphogenesis. For example, heterozygous missense mutations in the BMS1 gene induce autosomal dominant ACC. The Adams-Oliver syndrome (AOS) is defined as ACC with transverse terminal limb defects. Six causative mutations have been identified so far, comprising the genes ARHGAP31, DLL4, NOTCH1, RBPJ, DOCK6, and EOGT. Further associated anomalies consist of malformations of the central nervous system (CNS), congenital heart defects, cutis marmorata telangiectatica congenita, and other vascular anomalies. In non-familial cases hepatoportal sclerosis with portal hypertension and esophageal varices have been reported (Hassed et al. 2017). The rare autosomal dominant scalp-ear-nipple syndrome is char
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