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Next-generation sequencing in X-linked intellectual disability.

Andreas Tzschach1,2, Ute Grasshoff2, Stefanie Beck-Woedl2

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European Journal of Human Genetics : EJHG
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Summary

Genetic testing identified pathogenic variants in 13 X-linked intellectual disability (XLID) genes in 150 male patients. This study advances the genetic diagnosis of XLID, particularly in familial cases.

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Area of Science:

  • Genetics
  • Neuroscience
  • Medical Genomics

Background:

  • X-linked intellectual disability (XLID) is a complex genetic disorder with over 100 identified genes.
  • The genetic heterogeneity of XLID has historically made large-scale patient cohort screening challenging.
  • Identifying causative genes is crucial for accurate diagnosis and understanding disease mechanisms.

Purpose of the Study:

  • To systematically screen a cohort of 150 male patients for pathogenic variants in 107 known XLID genes.
  • To investigate the diagnostic yield of targeted next-generation sequencing in identifying XLID causes.
  • To explore the role of XLID genes in a female patient with severe intellectual disability and epilepsy.

Main Methods:

  • Targeted enrichment and next-generation sequencing of 107 XLID genes in 150 male patients (100 sporadic, 50 familial).
  • Analysis included a sporadic female patient with severe intellectual disability and skewed X-inactivation.
  • Gene dosage analysis was performed to detect deletions or duplications.

Main Results:

  • Pathogenic variants were identified in 13 XLID genes in 18 out of 150 male patients.
  • The diagnostic yield was higher in familial cases (26%) compared to sporadic cases (5%).
  • A pathogenic IQSEC2 variant was found in the female patient, suggesting its role in female encephalopathy; skewed X-inactivation was more common in mothers with pathogenic variants.

Conclusions:

  • Targeted next-generation sequencing is an effective method for diagnosing XLID, with a significant yield in familial cases.
  • The study identified 18 pathogenic variants across 13 XLID genes, expanding the known genetic landscape of the disorder.
  • Findings support the utility of XLID gene panels and highlight the importance of considering X-chromosomal defects in intellectual disability.