Compound heterozygote mutations in SPG7 in a family with adult-onset primary lateral sclerosis

Yi Yang, Lei Zhang, David R Lynch, Thomas Lukas, Kreshnik Ahmeti, Patrick M A Sleiman, Eanna Ryan, Kimberly A Schadt, Jordan H Newman, Han-Xiang Deng, Nailah Siddique, Teepu Siddique, Yi Yang, Lei Zhang, David R Lynch, Thomas Lukas, Kreshnik Ahmeti, Patrick M A Sleiman, Eanna Ryan, Kimberly A Schadt, Jordan H Newman, Han-Xiang Deng, Nailah Siddique, Teepu Siddique

Abstract

Objective: To identify the genetic defect for adult-onset primary lateral sclerosis (PLS) in a family with 5 patients.

Methods: Whole-exome sequencing was performed to identify the shared genetic variants in 3 affected members in a PLS family with 5 affected individuals. Sanger sequencing was used for validation of the variants and for cosegregation analysis. Mitochondrial activity for both patients and unaffected siblings was measured using a SeaHorse metabolic analyzer.

Results: Whole-exome sequencing and subsequent cosegregation analysis demonstrated that compound heterozygous missense variants L695P and I743T in SPG7 were the only mutations cosegregating with the disease in an autosomal recessive fashion in this family. The parents and siblings are genetically heterozygous and clinically unaffected. Functional studies suggested that the PLS-associated SPG7 mutants affect mitochondrial function when glucose is reduced.

Conclusions: Compound heterozygote mutations in SPG7 are associated with adult-onset PLS, extending the spectrum of SPG7-linked neurologic diseases. Patients with the PLS phenotype should have genetic testing for paraplegin, especially when the condition is familial.

Figures

Figure 1. Mutations in SPG7 in a… — **Figure 1. Mutations in *SPG7* in a family with primary lateral sclerosis**
(A) Pedigree with primary lateral sclerosis (PLS). DNA samples from 3 affected individuals (II-1, II-4, and II-7) were used for whole-exome sequencing. Candidate variants were validated, and cosegregation analysis was performed using the DNA samples from all 9 members of this family. The compound missense mutations, L695P and I743T, cosegregated with PLS in this family. (B) Sanger sequencing of *SPG7*. DNA and messenger RNA samples from lymphoblastoid cells from patients with PLS were Sanger-sequenced; heterozygous mutations are indicated by arrows. (+) = positive; (−) = absence; CF = cerebellar feature; LMN = lower motor neuron signs; NN = neurologically normal; WCB = wheelchair bound.

Figure 2. Increased mitochondrial sensitivity to glucose… — **Figure 2. Increased mitochondrial sensitivity to glucose reduction in lymphoblastoid cells from patients with primary lateral sclerosis**
(A) The mutated amino acids L695 and I743 are highly conserved in vertebrate species. Mutant amino acid residues are indicated by arrows. (B) Western blot was performed using the lysates of the lymphoblastoid cells from the unaffected heterozygous (lanes 1 and 2) and the affected compound heterozygous (lanes 3 and 4) individuals in this family. GAPDH was used as a loading control. The relative ratios of band density for SPG7 over GAPDH are shown in the right panel. (C, D) Oxygen consumption rate (OCR) assays. The OCR was measured under 4 conditions: basal, complex V inhibited, uncoupler stimulated, and in the presence of complex I and III inhibitors. The lymphoblastoid cells from 3 different patients and 2 unaffected heterozygous individuals were used in normal (C) or stress (D) conditions using the standard SeaHorse protocols. In all assays, cell adhesion was facilitated by using Cell-Tak-treated assay plates. The cells were allowed to attach for 1 hour before beginning the assay. *p < 0.05.

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Source: PubMed

Compound heterozygote mutations in SPG7 in a family with adult-onset primary lateral sclerosis

Abstract

Figures

References

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