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Case Reports
. 2017 May 30;88(22):2132-2140.
doi: 10.1212/WNL.0000000000003992. Epub 2017 May 3.

Novel Mutations in dystonin Provide Clues to the Pathomechanisms of HSAN-VI

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Free PMC article
Case Reports

Novel Mutations in dystonin Provide Clues to the Pathomechanisms of HSAN-VI

Fiore Manganelli et al. Neurology. .
Free PMC article

Abstract

Objective: To describe a second hereditary sensory autonomic neuropathy type VI (HSAN-VI) family harboring 2 novel heterozygous mutations in the dystonin (DST) gene and to evaluate their effect on neurons derived from induced pluripotent stem cells (iPSC).

Methods: The family consisted of 3 affected siblings from nonconsanguineous healthy parents. All members underwent clinical and electrophysiologic evaluation and genetic analysis. Two patients underwent quantitative sensory testing (QST), cardiovascular reflexes, dynamic sweat test, and skin biopsy to evaluate somatic and autonomic cutaneous innervation and to get fibroblast cultures for developing iPSC-derived neurons.

Results: Onset occurred in the first decade, with painless and progressive mutilating distal ulcerations leading to amputation and joint deformity. Sensation to pain, touch, and vibration was reduced. Autonomic disturbances included hypohidrosis, pupillary abnormalities, and gastrointestinal and sexual dysfunction. Nerve conduction studies showed a severe axonal sensory neuropathy. QST and autonomic functional studies were abnormal. Skin biopsy revealed a lack of sensory and autonomic nerve fibers. Genetic analysis revealed 2 pathogenic mutations in the DST gene affecting exclusively the DST neuronal isoform-a2. Neurons derived from iPSC showed absence or very low levels of DST protein and short and dystrophic neuritis or no projections at all.

Conclusions: Unlike the previous HSAN-VI family, our description indicates that DST mutations may be associated with a nonlethal and nonsyndromic phenotype. Neuronal loss affects large and small sensory nerve fibers as well as autonomic ones. Induced-PSC findings suggest that dystonin defect might alter proper development of the peripheral nerves. Dystonin-a2 plays a major role in the HSAN-VI phenotype.

Figures

Figure 1
Figure 1. Pedigree and genetic features
(A) Pedigree of the family with segregation analysis. (B) Pictures from patients show acromutilation and joint deformities. (C) Schematic diagram of DST gene. The putative promoters for the 3 neuronal isoforms (Dst-a1, -a2, -a3) are indicated by curved arrows. Blue boxes indicate the unique exons of isoform-a2, the red box indicates the unique exon of isoform-a1, and the green box indicates the unique exon of isoform-a3. The blue line represents the transcript of isoform-a2, the red line represents the transcript of isoform-a1, and the green line represents the transcript of isoform-a3. Full arrows show the position of mutations in our family, the empty arrow shows the mutation (exon 83, c.14865delA) previously reported in hereditary sensory and autonomic neuropathy type VI. (D) Chromatograms show the sequence of exon 4 and exon 5 from the affected members of the family.
Figure 2
Figure 2. Immunohistochemical study of skin innervation
Confocal images from fingertip (A, B, G, H) and leg (C, D, E, F) in a control (A, C, E, G) and in patient II-1 (B, D, F, H); and in green nerve fibers (protein gene product 9.5), in red basement membranes and vessels (COLIV), and in blue epidermis and endothelia (ULEX). In patient skin Meissner corpuscles (B compared to A), epidermal nerve fibers (D compared to C), nerves around sweat glands (F compared to E), and arteriovenous anastomosis (H compared to G) are absent. Scale bar = 100 μm.
Figure 3
Figure 3. Analysis of dystonin in normal and affected differentiated induced pluripotent stem cells (iPSC)
(A) Normal and affected undifferentiated iPSC were checked for the expression of stemness markers Oct4 and Nanog by immunostaining before differentiation. Scale bar, 100 μm. (B) Normal and affected differentiated iPSC were stained with a specific antibody against β-tubulin revealed by Alexa-488 conjugated secondary antibody. Images were collected by fluorescence microscopy. Scale bar, 50 μm. (C) Confocal images of normal and affected differentiated iPSC stained with β-tubulin (green) and dystonin (red). Scale bar, 10 μm. (D) Western blotting of dystonin in normal and affected differentiated iPSC. GAPDH is used as loading control. Molecular weight markers are indicated.

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