Hereditary Spastic Paraplegia Comprehensive Panel

Hereditary spastic paraplegia (HSP) is a group of clinically and genetically diverse diseases, characterized by bilateral lower extremity spasticity (rigid muscles) and weakness (Fink. 2014. PubMed ID: 25192507; Hensiek et al. 2015. PubMed ID: 25480570; Hedera. 2018. PubMed ID: 20301682). HSP is classified as “pure” or “uncomplicated” when symptoms are confined to lower extremity spasticity and weakness and hypertonic urinary bladder. In contrast, HSP is classified as “complex” or “complicated” if the impairments in the lower limbs are also accompanied by other systemic or neurologic abnormalities such as seizures, ataxia, intellectual disability, dementia, peripheral neuropathy, and vision and hearing impairment (Fink. 2014. PubMed ID: 20301682; Hedera. 2018. PubMed ID: 20301682). The incidence of all forms of HSP is estimated to be less than one in 10,000 individuals or 0.01% (Hensiek et al. 2015. PubMed ID: 25480570).

Symptoms of the disease may begin at any age, with early onset HSP beginning in early childhood and often resembling spastic diplegic cerebral palsy and late onset HSP beginning later in childhood or early adulthood (Fink. 2014. PubMed ID: 25192507; Hedera. 2018. PubMed ID: 20301682). In addition to variation in the age of onset, the severity and rate of progression are highly variable among different subtypes of complex HSPs, and even within a specific subtype (Tesson et al. 2015. PubMed ID: 25758904).

Advantages of genetic testing for HSP include confirmation of diagnosis, identification of other health risks associated with complicated HSP, allowing for targeted testing of other family members, and assistance with reproductive planning (Hedera. 2018. PubMed ID: 20301682). 

To date, more than 90 genetic loci and over 70 genes have been shown to be involved in HSP (Tesson et al. 2015. PubMed ID: 25758904; de Souza et al. 2017. PubMed ID: 27271711). HSP may be inherited in an autosomal dominant (AD) (75% to 80% of cases), autosomal recessive (AR) manner (25% to 30%); or X-linked (XL) (1% to 2%) manner (Hensiek et al. 2015. PubMed ID: 25480570; Hedera. 2018. PubMed ID: 20301682). The genotype-phenotype correlation is poor, and some genes are associated with both complex and pure HSP (Fink. 2013. PubMed ID: 23897027). 

See individual gene test descriptions for information on molecular biology of gene products and spectra of pathogenic variants.

This multi-gene panel analyzes 103 genes, including the most common genetic causes of Hereditary Spastic Paraplegia (HSP), such as SPAST, ATL1, SPG11, CYP7B1, KIF5A, REEP1, PGN, ZFYVE26 and L1CAM. These genes account for approximately 63% of affected individuals (Hedera. 2018. PubMed ID: 20301682). To increase the clinical sensitivity of the test, we also include genes identified more recently; however, each of these genes accounts for a small proportion of individuals with spastic paraplegia.

This test is performed using Next-Gen sequencing with additional Sanger sequencing as necessary.

This panel typically provides 99.7% coverage of all coding exons of the genes plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).

For technical reasons, exon 8 of the ABCD1 gene is not currently included in this panel.

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).