Hypoplastic hippocampus in atypical Rett syndrome with a novel FOXG1 mutation

The forkhead box G1 (FOXG1) gene encodes a brain-specific transcription factor and is associated with a congenital variant of atypical Rett syndrome (RTT); several FOXG1 mutations have been identified. The congenital variant of RTT shows a hypoplastic corpus callosum, delayed myelination, and frontal and temporal atrophy. Although no report has described a hippocampal abnormality in humans, the current study suggests that FOXG1 also regulates neurogenesis in the postnatal hippocampus. In the present case, severe developmental delay was observed in a patient with a congenital variant of RTT from about 4months, in conjunction with acquired microcephaly, hypotonia, limited motor function, absent purposeful hand use, and repetitive jerky movements of the upper limbs. A novel missense mutation was identified in FOXG1 on gene analysis (c. 569T>A, p. Ile190Asn). The patient showed not only the typical cerebral abnormalities of a congenital variant of RTT, but also a hypoplastic hippocampus. This novel mutation and cerebral findings may provide new insights into the pathophysiology of the congenital variant of RTT.