Hereditary spastic paraplegia (HSP) refers to a group of inherited disorders that cause weakness and stiffness of the leg muscles, which gradually gets worse over time.
A person with HSP is likely to have inherited an abnormal gene from their parents that causes the long nerves in their spine to deteriorate. These nerves control voluntary movement.
This means that muscles in the lower body do not receive the correct messages telling them to relax or contract. It leads to spasticity (abnormally stiff and rigid muscles) and weakness in the leg muscles, which progressively gets worse.
Most forms of HSP mainly affect the lower body - the arms and hands are usually unaffected.
On average, the symptoms of HSP start in mid-adulthood, although it can start as late as age 70 or in young children.
What are the symptoms?
Symptoms vary depending on the type of spastic paraplegia inherited.
At first there may just be mild stiffness and slight difficulty with walking, which slowly worsens to uncontrollable shaking of the legs when walking, poor balance and unsteadiness.
Many people with HSP develop foot drop, where they have difficulty lifting their toes and end up dragging them when they walk. They may keep tripping, especially if walking on uneven ground.
Some may eventually need a walking aid or wheelchair, although not everyone will.
Other symptoms in HSP are fatigue and bladder problems, such as incontinence or a sense of urgency.
How is it inherited?
Most people with HSP will have inherited an abnormal gene from their parents. Occasionally, HSP occurs as a result of an error when a child is conceived.
In most cases, a child with HSP will have inherited the faulty gene from just one of their parents, and this dominates over the corresponding normal gene they inherit from the other parent. This is known as autosomal dominant inheritance.
Sometimes, adults will carry a weaker version of the abnormal gene, which means they don't have symptoms but can pass on HSP to their children.
In some cases, a single copy of the faulty gene does not cause HSP. In these cases, children only develop HSP if they inherit the abnormal genes from both of their parents. This is known as autosomal recessive inheritance.
About 70-80% of cases of HSP result from autosomal dominant inheritance, and the remainder from autosomal recessive inheritance.
Can HSP be treated?
HSP cannot be prevented, slowed or reversed, but treatments can relieve some of the symptoms and help the person manage day-to-day activities. For example:
muscle relaxants such as baclofen and tizanidine and botulinum injections (Botox) can help relieve spasticity
physiotherapy is important for muscle strength and range of movement
a lower leg brace (ankle-foot orthosis) can help foot drop (read more about the treatment of foot drop)
surgery may occasionally be needed to release tendons or shortened muscles
The outlook for people with HSP varies. Some people are very disabled and need a wheelchair, while others only have a mild disability and do not need any walking aid.
Generally, many people with HSP lead relatively independent and active lives, even if they do need a wheelchair. HSP does not usually affect life expectancy.