PMC8415299_01
Clinical and functional impact of a known and novel mutation in XPA. (A) Face and arm photographs demonstrating prominent skin freckling or verrucous epidermal nevi. (B) MRI images showing no signs of pathology. (C) Representative image of EMG/nerve conduction tests indicating diffuse axonal sensorimotor polyneuropathy. (D) Sanger chromatogram demonstrating relevant mutations in both XPA alleles from the patient (arrows). (E) Nuclear family pedigree. (F) Location of XPA mutations. Schematic diagram of XPA protein with the functional domains of XPA. Each mutation gives rise to a premature stop codon. The corresponding amino acid numbers are shown below. (G) Mutations cause a loss of XPA in patient fibroblasts. Immunoblotting for XPA in patient dermal fibroblasts from suspected XP-A patient (XP1UMN) and an unrelated control (C1UMN). alpha-Tubulin was used as a loading control. Arrow denotes the specific band corresponding to XPA. (H) Measurement of UV-induced UDS in patient fibroblasts. Unscheduled DNA synthesis was measured in fibroblast lines, and the relative NER capacity is reported. NER capacity was normalized to those obtained for NER-proficient (C5RO) cells (set at 100%), and NER-deficient (XP51RO) control fibroblasts were used as a negative control. UDS was measured in duplicate for each cell line in three independent experiments. Values represent mean +- SD, ****p < 0.0001 by one-way ANOVA with Tukey's test.
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Skin examination showed a phototype 4 on the Fitzpatrick scale (Fitzpatrick,) and skin lesions (Figure 1A) including buttock hemangioma and common warts were present, although none was cancerous. Brain MRI (Figure 1B) showed no alterations while EMG and nerve conduction studies (Figure 1C) indicated diffuse axonal sensorimotor polyneuropathy. Our patient had compound heterozygous mutations in XPA (Figure 1D). Segregation analysis of the family confirmed compound heterozygous allele pairs (Figure 1E). The known mutation causes a stop codon in the C-terminal domain while the novel mutation creates a stop codon in the DNA-binding domain of XPA (Figure 1F). This combination of mutations dramatically reduced XPA protein abundance in dermal fibroblasts from the patient (XP1UMN) compared with those from an unrelated control (C1UMN) (Figure 1G). The patient fibroblasts (XP1UMN) had a significant reduction in UDS (3.03% +- 1.95%, p < 0.0001) compared with controls (C5RO = 100 +- 12.2; C1UMN = 118 +- 5.87), indicating significant NER impairment (Figure 1H).