Genotype-phenotype correlations of adult-onset PLA2G6-associated Neurodegeneration: case series and literature review

Abstract

Background: Phospholipase A2 group VI (PLA2G6) mutations associated with neurodegeneration (PLAN) manifest as heterogeneous neurodegenerative disorders with variable ages of onset. The genotype-phenotype correlation is not well-established. We aim to describe three adult patients with PLAN and combined these data with results from previous studies to elucidate adult-onset PLA2G6 phenotype-genotype correlations.

Case presentations: The first index patient presented with dystonia-parkinsonism starting at age 31 years, accompanied by major depression and cognitive decline. Genetic analysis using targeted next generation sequencing (NGS) panel, Sanger sequencing, and segregation analyses revealed a compound heterozygous mutation, c.991G > T (p.D331Y)/c.1077G > A (M358IfsX), in PLA2G6. The other two patients had levodopa-responsive, early-onset parkinsonism, starting in their late twenties. Both patients had homozygous c.991G > T (p.D331Y) mutations in PLA2G6. Patient characteristics of our reported 3 cases were compared to those of 32 previously described (2008 to 2019) patients with adult-onset PLAN. Among the combined cohort of 35 patients with adult-onset PLAN, 14 had dystonia-parkinsonism, 17 had early-onset Parkinson's disease, 3 had hereditary spastic paraparesis, and one had ataxia. The c.991G > T (p. D331Y) mutation was almost exclusively found in Chinese patients, suggesting a common founder effect. All patients with homozygous p.D331Y mutations had levodopa-responsive, early-onset PD (100%); while other mutations mostly led to dystonia-parkinsonism, ataxia, spasticity, and combine psychiatric comorbidities.

Conclusions: We showed that adult-onset PLAN could present as purely parkinsonism features, without brain iron accumulation, particularly patients with homozygous p.D331Y mutations. Compound heterozygous mutations, including heterozygous p.D331Y, produced heterogeneous phenotypes, without obvious levodopa responsiveness.

Keywords: Ataxia; Dystonia-parkinsonism; Early-onset parkinsonism; Hereditary spastic paraparesis; PLA2G6; PLA2G6-associated neurodegeneration.

Fig. 1

Family pedigree and genetic analysis of an index family. (a) Pedigree of an index family with compound heterozygous c.991G > T (p.Asp331Tyr) and c.1077G > A (M358IfsX) mutations in PLA2G6. WT, wild type. Open symbol: unaffected; filled symbol: affected; symbol with a diagonal line: deceased; diamond: total number of children, unknown sex; arrow: proband. (b) Sanger sequencing traces confirm the heterozygous PLA2G6 c.991G > T (p.Asp331Tyr) missense mutation. (c) Sanger sequencing traces confirm the heterozygous PLA2G6 c.1077G > A (M358IfsX) frame-shift mutation

Fig. 2

Brain imaging findings in the first index patient. (a, b, c) Brain MRIs with T2 Fluid Attenuated inversion recovery (FLAIR) sequence show (a) diffuse atrophy in the cortex and cerebellum and (b) cerebellar atrophy, but (c) no abnormal signs of iron accumulation in the globus pallidus. (d) A Tc-99 m TRODAT scan reveals reduced dopamine transporter activity in the bilateral basal ganglia