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Expanding phenotype of XNP mutations: mild to moderate mental retardation
Helger G Yntema1, Francis A Poppelaars, Esther Derksen
1Department of Human Genetics, University Medical Centre, Nijmegen, The Netherlands.
Abstract:
Mutations in the XNP gene have been reported in alpha thalassemia/mental retardation (MR) syndrome (ATR-X) and other severe X-linked MR conditions with facial dysmorphisms. In this report, we describe a missense mutation in exon 18 in a family with borderline to moderate MR. Like other disorders associated with an XNP mutation, skewed X-inactivation was found in all carrier females in this family. Only retrospective examination revealed childhood facial hypotonia and HbH inclusions in some of the affected males. These results expand the spectrum of clinical phenotypes known to be due to mutations in the XNP gene, and indicate that XNP mutation analysis should not be restricted to patients with severe MR and characteristic facial features.
Insights
Mutations in the XNP gene are linked to intellectual disability. This study identifies a new mutation in a family with milder symptoms, expanding the known clinical spectrum of XNP-related disorders.
Area of Science:
- Genetics
- Neurodevelopmental Disorders
- Molecular Biology
Background:
- Mutations in the XNP gene are associated with severe X-linked intellectual disability syndromes, such as alpha thalassemia/mental retardation (ATR-X) syndrome.
- These syndromes often present with distinct facial dysmorphisms and intellectual disability (MR).
Purpose of the Study:
- To investigate the clinical and genetic spectrum of XNP gene mutations.
- To identify the genetic cause of borderline to moderate intellectual disability in a specific family.
Main Methods:
- Genetic analysis to identify mutations in the XNP gene.
- X-inactivation studies in carrier females.
- Clinical evaluation of affected individuals, including retrospective assessment.
Main Results:
- A novel missense mutation in exon 18 of the XNP gene was identified in a family with borderline to moderate MR.
- Skewed X-inactivation was observed in all carrier females within the family.
- Retrospective analysis revealed subtle features like childhood facial hypotonia and HbH inclusions in some affected males.
Conclusions:
- The findings expand the spectrum of clinical phenotypes associated with XNP gene mutations.
- XNP mutation analysis should be considered even in cases of milder MR and less characteristic facial features.
- This broadens the diagnostic criteria for XNP-related disorders.