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Distal Xq duplication and functional Xq disomy
Damien Sanlaville1, Caroline Schluth-Bolard, Catherine Turleau
1Hospices Civils de Lyon, Centre de Biologie et de Pathologie Est, Service de Cytogénétique Constitutionnelle, Lyon, France. damien.sanlaville@chu-lyon.fr
Orphanet Journal of Rare Diseases
|February 24, 2009
Summary
Distal Xq duplications are X chromosome disorders with varied symptoms based on gender and gene content. The MECP2 gene in Xq28 is key to the abnormal phenotype, diagnosed via clinical features and CGH array.
Area of Science:
- Genetics
- Chromosomal Abnormalities
- Human Physiology
Background:
- Distal Xq duplications are chromosomal disorders affecting the X chromosome's long arm (Xq).
- Clinical presentations vary significantly with patient gender and the specific duplicated genetic material.
- The prevalence of Xq duplications is currently unknown, with approximately 40 cases of Xq28 functional disomy and 50 cases of cryptic duplications involving MECP2 reported.
Purpose of the Study:
- To describe the clinical manifestations, genetic causes, diagnostic approaches, and management strategies for distal Xq duplications.
- To highlight the role of the MECP2 gene in Xq28 as a primary driver of the associated phenotype.
- To inform clinicians about differential diagnoses, recurrence risks, and prenatal diagnostic options.
Main Methods:
- Review of reported cases and clinical features associated with distal Xq duplications.
- Genetic analysis, including cytogenetically visible rearrangements and cryptic duplications.
- Confirmation of diagnosis using array comparative genomic hybridization (CGH) techniques.
- Discussion of genetic mechanisms, including intrachromosomal duplication and translocations.
- Consideration of X chromosome dosage compensation mechanisms in females.
Main Results:
- The Xq28 segment is the most frequently duplicated region, leading to a recognizable phenotype.
- Key features include distinctive facial characteristics, severe hypotonia, developmental delay, feeding difficulties, and increased susceptibility to infections.
- The MECP2 gene in Xq28 is identified as the most significant dosage-sensitive gene contributing to the abnormal phenotype.
- Recurrence risk is elevated when a parent carries a structural rearrangement, often an intrachromosomal duplication from the mother.
Conclusions:
- Distal Xq duplications present a complex spectrum of clinical issues, heavily influenced by the MECP2 gene.
- Accurate diagnosis relies on clinical assessment corroborated by advanced genetic testing like array CGH.
- Management requires a multidisciplinary approach focused on symptomatic treatment, nutritional support, infection prevention, and developmental support.
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