Application of a Clinical Workflow May Lead to Increased Diagnostic Precision in Hereditary Spastic Paraplegias and Cerebellar Ataxias: A Single Center Experience

Abstract

The molecular characterization of Hereditary Spastic Paraplegias (HSP) and inherited cerebellar ataxias (CA) is challenged by their clinical and molecular heterogeneity. The recent application of Next Generation Sequencing (NGS) technologies is increasing the diagnostic rate, which can be influenced by patients' selection. To assess if a clinical diagnosis of CA/HSP received in a third-level reference center might impact the molecular diagnostic yield, we retrospectively evaluated the molecular diagnostic rate reached in our center on 192 unrelated families (90 HSP and 102 CA) (i) before NGS and (ii) with the use of NGS gene panels. Overall, 46.3% of families received a genetic diagnosis by first-tier individual gene screening: 43.3% HSP and 50% spinocerebellar ataxias (SCA). The diagnostic rate was 56.7% in AD-HSP, 55.5% in AR-HSP, and 21.2% in sporadic HSP. On the other hand, 75% AD-, 52% AR- and 33% sporadic CA were diagnosed. So far, 32 patients (24 CA and 8 HSP) were further assessed by NGS gene panels, and 34.4% were diagnosed, including 29.2% CA and 50% HSP patients. Eleven novel gene variants classified as (likely) pathogenic were identified. Our results support the role of experienced clinicians in the diagnostic assessment and the clinical research of CA and HSP even in the next generation era.

Keywords: HSP; NGS; SCA; ataxia; hereditary spastic paraplegia; neurogenetics.

Figure 1

Diagnostic flowchart applied to patients with suspected degenerative progressive spastic paraplegia (HSP) Abbreviations: NGS, Next Generation Sequencing; VLCFA, Very Long Chain Fatty Acids; AD, autosomal dominant; AR, autosomal recessive; TCC, thin corpus callosum; FRDA, Freidreich’s Ataxia; ARSACS, Autosomal recessive spastic ataxia of Charlevoix-Saguenay; MLPA, Multiplex Ligation Probe Amplification; HIV, Human Immunodeficiency Virus; AMN, adrenomyeloneuropathy.

Figure 2

Diagnostic flowchart applied at the suspected degenerative cerebellar ataxia patients. Abbreviations: SCA, SpinoCerebellar Ataxia; FRDA, Friedreich’s Ataxia; FXTAS, Fragile X-associated tremor/ataxia syndrome; AD, autosomal dominant; AR, autosomal recessive; ATM, ataxia-telangiectasia mutated; NPC, Niemann-Pick disease type C; AVED, Ataxia with vitamin E deficiency; RFC1, replication factor complex 1; NGS, Next-Generation Sequencing.

Figure 3

The pie-chart displays the results of individual gene screening in the HSP cohort, with an overall diagnostic yield of 43%. In black boxes, the relative percentages for each molecular diagnosis are reported; SPG4 was the most common HSP form, followed by SPG11 and SPG7.

Figure 4

Pie-chart showing the results of individual gene screening on the group degenerative ataxias. A molecular diagnosis was assessed in 52% of the whole cohort. In black boxes the relative percentages for each molecular diagnosis are reported; SCA2 and Friedreich’s ataxia were the most common genetic subtypes.

Figure 5

Schematic representation of the results of the diagnostic route in our cohort of SCA and HSP cases.