Families

Clinical and Genetic Characteristics
Changes (mutations) in the RELNgene can affect how the brain develops and functions.
This gene makes a protein called reelin, which helps brain cells move to the right place during early development and later supports brain in learning, memory, and the maintenance of synaptic connections. Different RELN changes can cause heterogeneous conditions:

•    Lissencephaly with cerebellar hypoplasia (LCH): a rare condition in which the brain surface looks smoother than usual and the cerebellum (the area that controls balance and coordination) is smaller.
•    Autosomal dominant lateral temporal epilepsy (ADLTE): a type of epilepsy that can run in families and often causes focal (partial) seizures.
•    ASD and others neuropsychiatric comorbidities: RELNis also being studied for its role in conditions like autism, schizophrenia, and Alzheimer’s disease, since it helps regulate how brain cells connect and communicate. While some genetic changes in RELN have been linked to these disorders, the evidence is still unconclusive, and its contribution appears to be only one piece of a much larger puzzle.

When both copies of the RELN gene are changed (homozygous variants), the condition is usually severe. Children may have a smoother brain surface, a very small cerebellum, severe developmental delay, difficulty moving or walking, and seizures. In some cases, MRI can also show changes in other brain regions such as the hippocampus or brainstem. When only one copy of the gene is changed (heterozygous variants), the symptoms are usually milder. These may include epilepsy, mild developmental delay, learning/behavioral problems and - less - brain MRI abnormalities. Some people who carry a single RELNchange may have no symptoms at all (incomplete penetrance).

Prevalence
RELN-related LCH is a very rare condition, with only a few families reported worldwide

Genetic Counseling
The way the condition is inherited depends on the type of mutation:

•    Autosomal recessive pattern, meaning a child must inherit two altered RELNcopies (one from each parent). Each pregnancy has a 25% chance of being affected.
•    Autosomal dominant pattern, meaning one altered copy is enough to cause symptoms. Each child of an affected parent has a 50% chance of inheriting the change, but as mentioned some individuals are unaffected even carrying the change.
•    If the RELNchange happened for the first time in the child (de novo), the risk for future pregnancies is low (<1%), though a very small chance remains because of possible germline mosaicism in a parent.
Families are encouraged to meet with a genetic counselor to discuss inheritance, family testing, and reproductive options.