Megalencephaly capillary malformation polymicrogyria (MCAP) syndrome is characterized by the sporadic occurrence of congenital and progressive megalencephaly, brain malformations including polymicrogyria, pre- and postnatal overgrowth with body asymmetry, cutaneous vascular malformations (including capillary malformation and cutis marmorata), digital anomalies connective tissue dysplasia (including skin and joint laxity), and developmental delay. In the past 10 years, the specific cause of the disease has been found in gain-of-function mutations of PIK3CA gene, mostly somatic/postzygotic but in rare cases also de novo germline. Such gene encodes for PI3K, a critical member of the PI3K-AKT-mTOR pathway: genetic changes lead to an over-activation of this signaling system, with increased vascular, limb, and brain cell development, progression, and survival. Interestingly, mutations in the same gene can cause other clinically heterogeneous syndromes, including CLOVE syndrome, macrodactyly, focal adipose overgrowth, epidermal nevi, facial infiltrating lipomatosis: all these syndromes (even if heterogeneous) are now considered a unique spectrum, known as PIK3CA-related overgrowth syndrome. On the contrary, a disease strictly similar to MCAP, characterized by megalencephaly, polymicrogyria, polydactyly, and hydrocephalus has been found to be caused by mutations in two other PI3K-AKT-mTOR-releted genes, AKT3 and PIK3R2, and for this reason is not included in the upper mentioned group of syndromes. With the exception of neurosurgery strategies for hydrocephalus and posterior fossa overcrowding, therapeutic options are nowadays limited, even if gene-targeted treatment protocols have been proposed and protocols with such agents (i.e., Arq092) are currently ongoing in small groups of patients with promising results.

The simultaneous occurrence of a patch of light or dark brown hyperpigmentation with hypertrichosis (Becker's nevus) together with (usually ipsilateral) soft tissues hypoplasia (especially breast, in women) and underlying skeletal anomalies (i.e., vertebral hypoplasia, scoliosis, pectus carinatum or excavatum) represents the Becker's nevus syndrome (BNS) phenotype. It was first described (as a single cutaneous lesion) by Becker in 1949 and then associated with the surrounding musculoskeletal disorders. The syndrome has also been reported as pigmentary hairy epidermal nevus syndrome. Less than 100 cases have been reported in the literature, with a slightly higher incidence in females and only few familiar cases: paradominant postzygotic mutations and/or an androgen-dependent hyperactivation have been reported as the causes of the diseases.The extracutaneous lesions are congenital and nonprogressive, and the natural history of the Becker's nevus is the same as that of isolated nevi: in prepubertal boys, the pigmentation may be less intense and the hairiness may be absent or mild, as occurs in women, whereas in men, there is an increase of hairiness after puberty. The treatment is essentially cosmetic, and potential therapeutic options include electrolysis, waxing, makeup, or laser.

Today the knowledge of genotype-phenotype correlation in cystic fibrosis is enriched by the growing discoveries of new mutations of the CFTR gene. Although the combination of two severe mutations usually leads to the classic disease (pulmonary and pancreatic insufficiency, sterility, nasal polyposis), the presence of a complex genotype characterized by severe and milder mutations or polymorphism can cause a hidden disease, which is often asymptomatic at early ages. We report on a case of a 15 years old boy, in whom the only clinical signs of CF were chronic hypertransaminasemia and hyperbilirubinemia, and in whom it was demonstrated the presence of the mutations F508del associated with TG11-9T-470M in one allele and TG12-5T-470V in the other allele. Although a clear genotype-phenotype correlation for liver disease is still missing for CF patients, it is possible to state that this isolated clinical presentation could represent an unusual phenotype of CF, related to a complex genotype characterized by a severe mutation and one (or more) polymorphism.

Wyburn–Mason syndrome is a very rare neurocutaneous disorder characterized by unilateral arteriovenous malformations of the midbrain associated with vascular abnormalities of eye and optic pathways, as well as multiple cutaneous nevi, reddish-bluish in color. The co-occurrence of such anomalies can be explained by an embryonic anomaly occurring in common ancestor cells, with the more severe cases related to development errors in the very early phases of gestation. Central nervous system and vision may be severely impaired: affected individuals may present with acute headache, hemiplegia, and homonymous hemianopsia in half of the cases. Seizures, cerebellar dysfunction, acute psychiatric signs, hallucinations, and temporal/spatial disorientation are reported more rarely. A progressive mental illness can become evident later in up to 30% of cases. Surgical removal is indicated only in superficially located arteriovenous malformations, while nonsurgical strategies (i.e., embolization and radiation therapy) are indicated for most of the lesions and represent the gold standard option in the treatment of this syndrome.

Speckled lentiginous nevus syndrome is a rare neurocutaneous phenotype, characterized by a specked lentiginous nevus, appearing as a light brown macule superimposed by multiple melanocytic nevi in the form of macules or papules with uneven distribution, associated with ipsilateral neurological and musculoskeletal abnormalities (i.e., dysesthesia, hyperhidrosis, and musculoskeletal abnormalities) occur. It represents a mosaic phenotype disorder resulting from postzygotic loss of heterozygosity, due to a localized defect in neural crest melanoblasts that originate certain areas of the skin and some ipsilateral neurological and musculoskeletal cells. Environmental and genetic factors may also play a role, but it has not been clarified how these factors behave in this syndrome.