Clinical pitfalls in the diagnosis of segmental overgrowth syndromes: a child with the c.2740G > A mutation in PIK3CA gene

Background: Overgrowth syndromes are known as a heterogeneous group of conditions characterized by a generalized or segmental, symmetric or asymmetric, overgrowth that may involve several tissues. These disorders, which present a wide range of phenotypic variability, are often caused by mosaic somatic mutations in the genes associated with the PI3K/AKT/mTOR cellular pathway, a signaling cascade that plays a key role in cellular growth. Overgrowth syndromes are frequently misdiagnosed. Given that they are also associated to an increased oncologic risk, it is important to distinguish the clinical characteristic of these disorders since the first months of life. Case presentation: We report the case of a seven-year-old male child with macrocephaly and right lateralized overgrowth, reported from birth. The patient arrived to our attention after an initial diagnosis of isolated benign macrocephaly was formulated at the age of 12 months. Afterwards, the child presented a moderate intellectual disability and pain episodes at right lower limb. We repeated a brain Magnetic Resonance Imaging that revealed ventriculomegaly, cerebellar tonsillar ectopia, a markedly thick corpus callosum, and white matter abnormalities. The diagnosis of segmental overgrowth syndrome was formulated according to the clinical presentation and confirmed by the finding of the variant c.2740G > A in the gene PIK3CA presented in somatic mosaicism. Conclusions: Our patient is the first children with the c.2740G > A variant in PIK3CA gene reported in Italy. We underline the importance of the genotype-phenotype correlation in the diagnostic process of overgrowth syndromes and emphasize the strict correlation between the mutation c.2740G > A in the PIK3CA gene and the Megalencephaly-Capillary Malformation syndrome phenotype.