Up to now, only five-point mutations in the MEF2C gene have been described in patients with severe mental retardation with absent speech, limited walking abilities, epilepsy, and lack of gross malformations. In brain, MEF2C is essential for early neurogenesis, neuronal migration, and differentiation. Here, we present a new patient with severe mental retardation, epilepsy, and hand stereotypies associated with a novel MEF2C frameshift mutation c.457delA. The purpose of this work was to clarify criteria for the selection of patients with severe intellectual disability to screen for deficiency in the MEF2C gene. By combining the clinical data of all patients with MEF2C point mutations published so far with the phenotype of our patient, a targeted search for MEF2C mutations could be applied to patients with a severe intellectual deficiency associated with absence of language and hypotonia, strabismus, and epilepsy (started after 6 months, often well controlled by valproate).

Mutations in the cyclin-dependent kinase-like 5 gene (CDKL5) have been described in epileptic encephalopathies in females with infantile spasms with features that overlap with Rett syndrome. With more than 80 reported patients, the phenotype of CDKL5-related encephalopathy is well-defined. The main features consist of seizures starting before 6 months of age, severe intellectual disability with absent speech and hand stereotypies and deceleration of head growth, which resembles Rett syndrome. However, some clinical discrepancies suggested the influence of genetics and/or environmental factors. No genotype-phenotype correlation has been defined and thus there is a need to examine individual mutations. In this study, we analyzed eight recurrent CDKL5 mutations to test whether the clinical phenotype of patients with the same mutation is similar and whether patients with specific CDKL5 mutations have a milder phenotype than those with other CDKL5 mutations. Patients bearing missense mutations in the ATP binding site such as the p.Ala40Val mutation typically walked unaided, had normocephaly, better hand use ability, and less frequent refractory epilepsy when compared to girls with other CDKL5 mutations. In contrast, patients with mutations in the kinase domain (such as p.Arg59X, p.Arg134X, p.Arg178Trp/Pro/Gln, or c.145 + 2T > C) and frameshift mutations in the C-terminal region (such as c.2635_2636delCT) had a more severe phenotype with infantile spasms, refractory epileptic encephalopathy, absolute microcephaly, and inability to walk. It is important for clinicians to have this information when such patients are diagnosed.

Mutations in the FOXG1 gene have been shown to cause congenital variant of Rett syndrome. To date, point mutations have been reported only in female patients. We screened the entire coding region of the gene for mutations in 50 boys with congenital encephalopathy, postnatal microcephaly, and complex movement disorders, a clinical picture very similar to that described in girls with FOXG1 mutations. We found one boy carrying the de novo c.256_257dupC frameshift mutation. He presented the association of postnatal microcephaly, severe axial dystonia with severe feeding difficulties with protruding tongue movements during the first year of life that subsequently evolved into dyskinetic movement disorders with hand stereotypies. In contrast to his severe motor impairment, he developed nonverbal communication skills and relative good eye contact. Brain MRI showed frontal gyral simplification with dramatic myelination delay most prominent in both frontal lobes. Altogether the presentation in this male patient is highly reminiscent of that observed in FOXG1-mutated females with the congenital variant of Rett syndrome. This new case confirms the prediction that congenital variant of Rett syndrome should be found also in males, with the characteristic hallmarks consisting of postnatal microcephaly, dyskinetic movement disorder with Rett-like features, i.e., hand stereotypies, and frontal gyral simplification with myelination delay. FOXG1 screening should be considered in individuals with these clinical features.