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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

Co-segregation of a variant in MUSK with lethal FADS in a Dutch genetic isolate. (a) Schematic illustrating the common ancestry of 14 affected fetuses from 11 families. (b) Sanger sequencing chromatograms of fetal (top) and parental (bottom) DNA samples identifying the variant NM_005592.3: c.1724T>C; p.(Ile575Thr) and multispecies alignment of the affected residue (right). (c) Domain structure of MUSK depicting the extracellular domain containing IgG-like domains, a Frizzled domain (FZ, also named C6 box), a transmembrane domain (TM) and a cytoplasmic domain that contains a juxtamembrane (JM)/PTB-domain and the tyrosine kinase domain. Ile575 is located at the boundary between the JM and kinase domains, very close to the Dok7-interacting region and the autophosphorylation site Tyr554. Other mutations previously reported to cause CMS are also indicated. Mutations found in compound heterozygotes are color-matched23, 24, 25, 26, 27, 28. All amino-acid numbers refer to MUSK isoform 1 (GenPept accession NP_005583.1).
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fig1: Co-segregation of a variant in MUSK with lethal FADS in a Dutch genetic isolate. (a) Schematic illustrating the common ancestry of 14 affected fetuses from 11 families. (b) Sanger sequencing chromatograms of fetal (top) and parental (bottom) DNA samples identifying the variant NM_005592.3: c.1724T>C; p.(Ile575Thr) and multispecies alignment of the affected residue (right). (c) Domain structure of MUSK depicting the extracellular domain containing IgG-like domains, a Frizzled domain (FZ, also named C6 box), a transmembrane domain (TM) and a cytoplasmic domain that contains a juxtamembrane (JM)/PTB-domain and the tyrosine kinase domain. Ile575 is located at the boundary between the JM and kinase domains, very close to the Dok7-interacting region and the autophosphorylation site Tyr554. Other mutations previously reported to cause CMS are also indicated. Mutations found in compound heterozygotes are color-matched23, 24, 25, 26, 27, 28. All amino-acid numbers refer to MUSK isoform 1 (GenPept accession NP_005583.1).

Mentions: Homozygosity mapping in two fetuses with FADS from a single consanguineous family (case 10 and 11 in Table 1 and Figure 1a) identified MUSK as the prime candidate gene. Sanger sequencing revealed a novel homozygous missense variant (NM_005592.3: c.1724T>C; p.(Ile575Thr); Figure 1b) absent in relevant databases (dbSNP build 132, 1000 Genomes project, and Exome Variant Server data ESP5400). The amino-acid change was predicted to be potentially pathogenic by various bioinformatics tools: SIFT: Deleterious (score: 0, median: 4.32); Align GVGD: C65 (GV: 0.00–GD: 89.28); PhyloP: 4.97 (highly conserved); Mutation Taster: disease causing, prob: 0.9999999987; Polyphen: probably damaging (HumVar score 0.999). The variant was also absent in a cohort of 1326 Dutch controls, analyzed by Taqman SNP Genotyping (Life Technologies).


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)

Co-segregation of a variant in MUSK with lethal FADS in a Dutch genetic isolate. (a) Schematic illustrating the common ancestry of 14 affected fetuses from 11 families. (b) Sanger sequencing chromatograms of fetal (top) and parental (bottom) DNA samples identifying the variant NM_005592.3: c.1724T>C; p.(Ile575Thr) and multispecies alignment of the affected residue (right). (c) Domain structure of MUSK depicting the extracellular domain containing IgG-like domains, a Frizzled domain (FZ, also named C6 box), a transmembrane domain (TM) and a cytoplasmic domain that contains a juxtamembrane (JM)/PTB-domain and the tyrosine kinase domain. Ile575 is located at the boundary between the JM and kinase domains, very close to the Dok7-interacting region and the autophosphorylation site Tyr554. Other mutations previously reported to cause CMS are also indicated. Mutations found in compound heterozygotes are color-matched23, 24, 25, 26, 27, 28. All amino-acid numbers refer to MUSK isoform 1 (GenPept accession NP_005583.1).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4538208&req=5

fig1: Co-segregation of a variant in MUSK with lethal FADS in a Dutch genetic isolate. (a) Schematic illustrating the common ancestry of 14 affected fetuses from 11 families. (b) Sanger sequencing chromatograms of fetal (top) and parental (bottom) DNA samples identifying the variant NM_005592.3: c.1724T>C; p.(Ile575Thr) and multispecies alignment of the affected residue (right). (c) Domain structure of MUSK depicting the extracellular domain containing IgG-like domains, a Frizzled domain (FZ, also named C6 box), a transmembrane domain (TM) and a cytoplasmic domain that contains a juxtamembrane (JM)/PTB-domain and the tyrosine kinase domain. Ile575 is located at the boundary between the JM and kinase domains, very close to the Dok7-interacting region and the autophosphorylation site Tyr554. Other mutations previously reported to cause CMS are also indicated. Mutations found in compound heterozygotes are color-matched23, 24, 25, 26, 27, 28. All amino-acid numbers refer to MUSK isoform 1 (GenPept accession NP_005583.1).
Mentions: Homozygosity mapping in two fetuses with FADS from a single consanguineous family (case 10 and 11 in Table 1 and Figure 1a) identified MUSK as the prime candidate gene. Sanger sequencing revealed a novel homozygous missense variant (NM_005592.3: c.1724T>C; p.(Ile575Thr); Figure 1b) absent in relevant databases (dbSNP build 132, 1000 Genomes project, and Exome Variant Server data ESP5400). The amino-acid change was predicted to be potentially pathogenic by various bioinformatics tools: SIFT: Deleterious (score: 0, median: 4.32); Align GVGD: C65 (GV: 0.00–GD: 89.28); PhyloP: 4.97 (highly conserved); Mutation Taster: disease causing, prob: 0.9999999987; Polyphen: probably damaging (HumVar score 0.999). The variant was also absent in a cohort of 1326 Dutch controls, analyzed by Taqman SNP Genotyping (Life Technologies).

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