Families

Clinical features
This condition can vary a lot from person to person. In the most severe cases, it can affect a baby before birth and may even be life-threatening. In milder cases, people may live into adulthood with less severe symptoms.

Common features include:
•    Low muscle tone in newborns (they feel “floppy”)
•    Delays in learning and development
•    Intellectual disability (ranging from mild to more significant)

As people grow, many develop increasing stiffness and weakness in their muscles:
•    This often affects the legs (spastic paraplegia) or sometimes all four limbs (tetraplegia)
•    Some people instead have problems with balance and coordination (ataxia)

Other possible features:
•    Anxiety or traits similar to autism
•    Brain scans may show changes (like loss of white matter or thinning of a structure called the corpus callosum), sometimes even when symptoms are not very obvious

Milder cases: Some individuals have only mild learning difficulties or nearly normal thinking ability. Symptoms may start early but usually worsen slowly.

Families with this condition may have a higher number of miscarriages, suggesting the gene involved is very important for early development.

How common is it?
It’s extremely rare. One main study found only 13 people from 8 unrelated families.

What causes it (inheritance)?
•    It is caused by changes in a gene called RPS6KC1.
•    A child needs to inherit two altered copies (one from each parent) to have the condition.
•    This is called autosomal recessive inheritance.
•    Parents are usually healthy carriers (they each have one altered copy but no symptoms).