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Identification of a Dutch founder mutation in MUSK causing fetal akinesia deformation sequence.

Tan-Sindhunata MB, Mathijssen IB, Smit M, Baas F, de Vries JI, van der Voorn JP, Kluijt I, Hagen MA, Blom EW, Sistermans E, Meijers-Heijboer H, Waisfisz Q, Weiss MM, Groffen AJ - Eur. J. Hum. Genet. (2014)

Bottom Line: The carrier frequency in the genetic isolate was 8%, exclusively found in heterozygous carriers.Consistent with the established role of MUSK as a tyrosine kinase that orchestrates neuromuscular synaptogenesis, the fetal myopathy was accompanied by impaired acetylcholine receptor clustering and reduced tyrosine kinase activity at motor nerve endings.Taken together, the results strongly support a causal role of this founder mutation in MUSK, further expanding the gene set associated with FADS and offering new opportunities for prenatal genetic testing.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Genetics, VU University Medical Center, Amsterdam, The Netherlands.

ABSTRACT
Fetal akinesia deformation sequence (FADS) refers to a clinically and genetically heterogeneous group of disorders with congenital malformations related to impaired fetal movement. FADS can result from mutations in CHRNG, CHRNA1, CHRND, DOK7 and RAPSN; however, these genes only account for a minority of cases. Here we identify MUSK as a novel cause of lethal FADS. Fourteen affected fetuses from a Dutch genetic isolate were traced back to common ancestors 11 generations ago. Homozygosity mapping in two fetuses revealed MUSK as a candidate gene. All tested cases carried an identical homozygous variant c.1724T>C; p.(Ile575Thr) in the intracellular domain of MUSK. The carrier frequency in the genetic isolate was 8%, exclusively found in heterozygous carriers. Consistent with the established role of MUSK as a tyrosine kinase that orchestrates neuromuscular synaptogenesis, the fetal myopathy was accompanied by impaired acetylcholine receptor clustering and reduced tyrosine kinase activity at motor nerve endings. A functional assay in myocytes derived from human fetuses confirmed that the variant blocks MUSK-dependent motor endplate formation. Taken together, the results strongly support a causal role of this founder mutation in MUSK, further expanding the gene set associated with FADS and offering new opportunities for prenatal genetic testing.

No MeSH data available.


Related in: MedlinePlus

Histopathological findings indicative for defects in neuromuscular synaptogenesis. (a) Skeletal muscle biopsies showed small and rounded atrophic fibers and an increased number of intracellular nuclei (arrowheads). (b and c) Immunostaining of type I (b) and type II fibers (c) indicated a relative loss of type I fibers. (d–g) Combined staining for nerve terminals (synaptotagmin-1) and AChR clusters (α-bungarotoxin-rhodamine) in quadriceps muscle indicated fewer and smaller neuromuscular junctions in case 8 (arrowheads in d, e; 23 weeks of gestation) compared with a control fetus (f, g; 22 weeks). (h–k) Combined staining for nerve terminals, AChR clusters and anti-phosphotyrosine (pTyr) monoclonal 4G10 in diaphragm indicated fewer clusters (arrowheads) and a loss of tyrosine kinase activity in MUSKI575T/I575T endplates (h, i) compared with control tissue (j, k). Note that residual tyrosine kinase activity was detected in some mutant endplates (arrow), which may also result from unrelated tyrosine kinases.
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fig3: Histopathological findings indicative for defects in neuromuscular synaptogenesis. (a) Skeletal muscle biopsies showed small and rounded atrophic fibers and an increased number of intracellular nuclei (arrowheads). (b and c) Immunostaining of type I (b) and type II fibers (c) indicated a relative loss of type I fibers. (d–g) Combined staining for nerve terminals (synaptotagmin-1) and AChR clusters (α-bungarotoxin-rhodamine) in quadriceps muscle indicated fewer and smaller neuromuscular junctions in case 8 (arrowheads in d, e; 23 weeks of gestation) compared with a control fetus (f, g; 22 weeks). (h–k) Combined staining for nerve terminals, AChR clusters and anti-phosphotyrosine (pTyr) monoclonal 4G10 in diaphragm indicated fewer clusters (arrowheads) and a loss of tyrosine kinase activity in MUSKI575T/I575T endplates (h, i) compared with control tissue (j, k). Note that residual tyrosine kinase activity was detected in some mutant endplates (arrow), which may also result from unrelated tyrosine kinases.

Mentions: Microscopic examination of tissues from case 8 (a terminated pregnancy at 23 weeks of gestation) showed no abnormalities of the cerebrum, cerebellum, cranial nerve motor nuclei and spinal motor neurons. In contrast, muscle tissues (m. quadriceps, m. psoas, m. biceps femoris, diaphragm) showed several myopathic features consistent with a denervating or neurogenic cause (Figure 3). There was clear variation in muscle fiber diameter with small and rounded shaped atrophic fibers and there was a mild increase in endomysial fibrosis. The number of internal nuclei was increased consistent with maturational delay. The ratio between type 1 and 2 fibers was 1:10 suggesting a loss of type 1 (slow) fibers (Figure 3b and c).


Identification of a Dutch founder mutation in MUSK causing fetal akinesia deformation sequence.

Tan-Sindhunata MB, Mathijssen IB, Smit M, Baas F, de Vries JI, van der Voorn JP, Kluijt I, Hagen MA, Blom EW, Sistermans E, Meijers-Heijboer H, Waisfisz Q, Weiss MM, Groffen AJ - Eur. J. Hum. Genet. (2014)

Histopathological findings indicative for defects in neuromuscular synaptogenesis. (a) Skeletal muscle biopsies showed small and rounded atrophic fibers and an increased number of intracellular nuclei (arrowheads). (b and c) Immunostaining of type I (b) and type II fibers (c) indicated a relative loss of type I fibers. (d–g) Combined staining for nerve terminals (synaptotagmin-1) and AChR clusters (α-bungarotoxin-rhodamine) in quadriceps muscle indicated fewer and smaller neuromuscular junctions in case 8 (arrowheads in d, e; 23 weeks of gestation) compared with a control fetus (f, g; 22 weeks). (h–k) Combined staining for nerve terminals, AChR clusters and anti-phosphotyrosine (pTyr) monoclonal 4G10 in diaphragm indicated fewer clusters (arrowheads) and a loss of tyrosine kinase activity in MUSKI575T/I575T endplates (h, i) compared with control tissue (j, k). Note that residual tyrosine kinase activity was detected in some mutant endplates (arrow), which may also result from unrelated tyrosine kinases.
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Related In: Results  -  Collection

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fig3: Histopathological findings indicative for defects in neuromuscular synaptogenesis. (a) Skeletal muscle biopsies showed small and rounded atrophic fibers and an increased number of intracellular nuclei (arrowheads). (b and c) Immunostaining of type I (b) and type II fibers (c) indicated a relative loss of type I fibers. (d–g) Combined staining for nerve terminals (synaptotagmin-1) and AChR clusters (α-bungarotoxin-rhodamine) in quadriceps muscle indicated fewer and smaller neuromuscular junctions in case 8 (arrowheads in d, e; 23 weeks of gestation) compared with a control fetus (f, g; 22 weeks). (h–k) Combined staining for nerve terminals, AChR clusters and anti-phosphotyrosine (pTyr) monoclonal 4G10 in diaphragm indicated fewer clusters (arrowheads) and a loss of tyrosine kinase activity in MUSKI575T/I575T endplates (h, i) compared with control tissue (j, k). Note that residual tyrosine kinase activity was detected in some mutant endplates (arrow), which may also result from unrelated tyrosine kinases.
Mentions: Microscopic examination of tissues from case 8 (a terminated pregnancy at 23 weeks of gestation) showed no abnormalities of the cerebrum, cerebellum, cranial nerve motor nuclei and spinal motor neurons. In contrast, muscle tissues (m. quadriceps, m. psoas, m. biceps femoris, diaphragm) showed several myopathic features consistent with a denervating or neurogenic cause (Figure 3). There was clear variation in muscle fiber diameter with small and rounded shaped atrophic fibers and there was a mild increase in endomysial fibrosis. The number of internal nuclei was increased consistent with maturational delay. The ratio between type 1 and 2 fibers was 1:10 suggesting a loss of type 1 (slow) fibers (Figure 3b and c).

Bottom Line: The carrier frequency in the genetic isolate was 8%, exclusively found in heterozygous carriers.Consistent with the established role of MUSK as a tyrosine kinase that orchestrates neuromuscular synaptogenesis, the fetal myopathy was accompanied by impaired acetylcholine receptor clustering and reduced tyrosine kinase activity at motor nerve endings.Taken together, the results strongly support a causal role of this founder mutation in MUSK, further expanding the gene set associated with FADS and offering new opportunities for prenatal genetic testing.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Genetics, VU University Medical Center, Amsterdam, The Netherlands.

ABSTRACT
Fetal akinesia deformation sequence (FADS) refers to a clinically and genetically heterogeneous group of disorders with congenital malformations related to impaired fetal movement. FADS can result from mutations in CHRNG, CHRNA1, CHRND, DOK7 and RAPSN; however, these genes only account for a minority of cases. Here we identify MUSK as a novel cause of lethal FADS. Fourteen affected fetuses from a Dutch genetic isolate were traced back to common ancestors 11 generations ago. Homozygosity mapping in two fetuses revealed MUSK as a candidate gene. All tested cases carried an identical homozygous variant c.1724T>C; p.(Ile575Thr) in the intracellular domain of MUSK. The carrier frequency in the genetic isolate was 8%, exclusively found in heterozygous carriers. Consistent with the established role of MUSK as a tyrosine kinase that orchestrates neuromuscular synaptogenesis, the fetal myopathy was accompanied by impaired acetylcholine receptor clustering and reduced tyrosine kinase activity at motor nerve endings. A functional assay in myocytes derived from human fetuses confirmed that the variant blocks MUSK-dependent motor endplate formation. Taken together, the results strongly support a causal role of this founder mutation in MUSK, further expanding the gene set associated with FADS and offering new opportunities for prenatal genetic testing.

No MeSH data available.


Related in: MedlinePlus