PA15 Becker naevus syndrome associated with a mosaic pathogenic variant in <i>ACTB</i>

Abstract A 15-year-old girl presented with an 8-year history of a gradually enlarging, irregular, nonconfluent hyperpigmented patch on her left flank. The lesion demonstrated area increased hair growth, did not cross the midline and was mildly pruritic but otherwise asymptomatic. Another pigmented patch, present since birth, also noted right lower back consistent café-au-lait macule. Medical included marfanoid phenotype musculoskeletal complications including scoliosis joint hypermobility, for which she under care orthopaedic team bilateral patellar instability associated recurrent dislocation. She to have skin laxity, mild pectus excavatum, mitral valve prolapse symptomatic tachyarrhythmias. born at term, nonconsanguineous parents, no postnatal developmental concerns. There family older brother significant hip dysplasia requiring replacements, developing from age 14 years. Genetic testing negative FBN1 five other genes Marfan syndrome. Thyroid function bone profile were normal. Menarche occurred 11 years age, full hormone normal except raised prolactin level, deemed be variant in puberty. Abdominal pelvic ultrasounds Skin biopsy flank revealed orthokeratosis, irregular elongation rete ridges sparse perivascular chronic inflammation superficial dermis. Next-generation sequencing droplet digital polymerase chain reaction DNA extracted de novo mosaic pathogenic variants ACTB, encodes β-actin, intracellular protein involved cell migration, signalling proliferation. Recurrent ACTB previously been 61% Becker naevi one case naevus syndrome study (Cai ED, Sun BK, Chian et al. Postzygotic mutations beta-actin are Becker’s nevus Nevus J Invest Dermatol 2017; 137:1795–8), as well congenital smooth muscle hamartomas odontomaxillary dysplasia. Our patient had cutaneous extracutaneous features suggestive This rare predominantly involves skeletal soft tissue abnormalities, breast hypoplasia most frequently reported. Notable here include macule, excavatum. highlights value analysis confirming diagnosis, after 9 presentation paediatric services. Given heterogeneous phenotypes, there important implications counselling screening conditions.