lissencephalic

Lissencephalic is an adjective used to describe a brain whose surface is abnormally smooth, lacking the normal folds or gyri and grooves called sulci. The term is often used in reference to lissencephaly, a developmental brain malformation that results from disrupted neuronal migration during early fetal life.

Lissencephaly arises from genetic or chromosomal abnormalities that interfere with how neurons migrate to their final positions in the cerebral cortex. Known causative genes include LIS1 (PAFAH1B1), DCX, TUBA1A, RELN, and ARX, among others. The condition can occur in isolation or as part of larger syndromes such as Miller-Dieker syndrome, which involves deletions affecting multiple genes. The neurological outcome depends on the extent and pattern of cortical disruption.

Pathologically, lissencephaly may present as agyria (complete absence of gyri) or pachygyria (bewerly formed, broad gyri). Imaging, particularly magnetic resonance imaging (MRI), shows a thickened, smooth cortex with a simplified gyral pattern and often other accompanying brain malformations. These structural abnormalities underlie the clinical picture.

Clinically, individuals with lissencephaly typically present in infancy with hypotonia, seizures, and varying degrees of developmental delay or intellectual disability. Microcephaly may be present, and the severity is related to the extent of cortical misorganization. There is no cure; management focuses on supportive care, including seizure control and therapies to maximize motor and cognitive development.

Lissencephalic is used broadly in human and veterinary medicine to describe species with smooth-brained cerebral anatomy, reflecting a spectrum of disorders tied to disrupted cortical development.