The diagnosis of our patient is Klippel–Trénaunay syndrome (KTS). Diagnosis of KTS is often made clinically, based on the classic triad of capillary malformation (port-wine stain), venous malformation and limb overgrowth with or without lymphatic involvement (discussed below).1 Sometimes, patients may only present two out of three features. Radiologic evaluation such as ultrasonography and MRI used to characterise vascular anomalies; laboratory testing such as elevated D-dimer level used to identify venous malformation, are also useful in securing a diagnosis. KTS can also be confirmed by molecular testing of the PIK3CA gene. In our patient, exome sequencing of DNA extracted from the surgical tissue revealed a somatic mosaic mutation in the PIK3CA gene (PIK3CA: p.(Asn1068Lysfs*5), level of mosaicism at 6%). It is a deletion of 11 nucleotides that shifts the reading frame of protein translation (frameshift mutation), which eventually reaches a stop codon five amino acids after the deletion (Figure 2). Differential diagnosis of KTS includes syndromes associated with vascular malformation such as diffuse capillary malformation with overgrowth (DCMO), Parkes Weber syndrome and other overgrowth syndromes.
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