What is Hereditary Spastic Paraplegia?
Hereditary Spastic Paraplegia (HSP) is a broad group of inherited, degenerative disorders characterised by impaired walking due to spasticity and weakness of the legs.
The primary features of HSP are spasticity and weakness with the proportions varying from individual to individual. HSP is a progressive condition, meaning that the disease gets worse over time, as do the symptoms, though by how much and how fast is highly variable between people, even in the one family with the same HSP type.
Diagnosis is primarily by clinical neurological examination and testing as there are similarities with a number of other disorders. In the early stages of disease onset, the symptoms of HSP are very similar to several other conditions, making diagnosis difficult and sometimes impossible. Perhaps half of all people with HSP report having been misdiagnosed at least once, whilst the time to get a definitive diagnosis is likely 2 – 4 years on average.
Genetic testing for HSP is now high-quality, widely available and relatively affordable. The detection rate of HSP mutations is in the 50–60% range with comprehensive HSP gene panels and increasingly sophisticated and sensitive genetic testing technologies available. However, despite these, a substantial proportion of all cases of HSP do not return a positive genetic test result.
Also known as
Hereditary Spastic Paraplegia (HSP) is also called Familial Spastic Paraplegia or Paraparesis (FSP) and Strumpell-Lorraine Syndrome, as well as other less commonly used names including Spastic Paraplegia, Hereditary Charcot-Disease, Spastic Spinal Paralysis, Diplegia Spinalis Progressiva, French Settlement Disease, Troyer syndrome, and Silver syndrome. Hereditary Spastic Paraplegia is the most common name used in the USA, UK and Australia.
Prevalence
The disease has been reported in nearly every country. Frequency estimates vary widely (from 0.5 to 12 people per 100,000 of population) and are an estimate or approximation as highly reliable data are not available. Based on what we consider to be the most applicable evidence on prevalence, a rate of 7.4/100,000 of population is used. No significant differences in rate relating to gender have been found in most population studies, however in at least one larger study, prevalence in males was found to be somewhat higher. Average age of symptom onset is 24 years old. There is also juvenile onset HSP which can show up in children of any age and tends to be associated with more severe symptoms as well as a larger range of symptoms, including affecting the upper limbs and sometimes sight, speech, swallowing and cognitive impairment.
Extrapolated to the Australian population, this translates to about 1,775 HSPers, with over 500,000 globally. Every 3 weeks in Australia a child is born with an HSP mutation.
Being rare, it is a low profile disease globally, largely unknown in the general population, and receiving little, though significantly increasing, medical research attention. With current estimates of the number of rare diseases well over 6,000 (80% of which are genetic) most rare disease organisations and support groups find themselves in similar situations to ours.
Worldwide, HSP is thought to be under-diagnosed as mild cases, which go undiagnosed, exist. Around 15% of people with HSP mutations, quoted in some places as high as 25%, never show symptoms. Misdiagnosis – commonly as Multiple Sclerosis, Cerebral Palsy or Primary Lateral Sclerosis – is not uncommon, while some HSP diagnoses prove to be incorrect. Overall, total numbers with HSP are likely to be underestimated.