Deletions in Xq26.3-q27.3 including FMR1 result in a severe phenotype in a male and variable phenotypes in females depending upon the X inactivation pattern.
High resolution cytogenetics, microsatellite marker analyses, and fluorescence in situ hybridization were used to define Xq deletions encompassing the fragile X gene, FMR1, detected in individuals from two unrelated families. In Family 1, a 19-year-old male had facial features consistent with fragile X syndrome; however, his profound mental and growth retardation, small testes, and lover limb skeletal defects and contractures demonstrated a more severe phenotype, suggestive of a contiguous gene syndrome. A cytogenetic deletion including Xq26.3-q27.3 was observed in the proband, his phenotypically normal mother, and his learning-disabled non-dysmorphic sister. Methylation analyses at the FMR1 and androgen receptor loci indicated that the deleted X was inactive in > 95% of his mother's white blood cells and 80-85% of the sister's leukocytes. The proximal breakpoint for the deletion was approximately 10 Mb centromeric to FMR1, and the distal breakpoint mapped 1 Mb distal to FMR1. This deletion, encompassing approximately 13 Mb of DNA, is the largest deletion including FMR1 reported to date. In the second family, a slightly smaller deletion was detected. A female with moderate to severe mental retardation, seizures, and hypothyroidism, had a de novo cytogenetic deletion extending from Xq26.3 to q27.3, which removed approximately 12 Mb of DNA around the FMR1 gene. Cytogenetic, and molecular data revealed that approximately 50% of her white blood cells contained an active deleted X. These findings indicate that males with deletions including Xq26.3-q27.3 may exhibit a more severe phenotype than typical fragile X males, and females with similar deletions may have an abnormal phenotype if the deleted X remains active in a significant proportion of the cells. Thus, important genes for intellectual and neurological development, in addition to FMR1, may reside in Xq26.3-q27. 3. One candidate gene in this region, SOX3, is thought to be involved in neuronal development and its loss may partly explain the more severe phenotypes of our patients.[1]References
- Deletions in Xq26.3-q27.3 including FMR1 result in a severe phenotype in a male and variable phenotypes in females depending upon the X inactivation pattern. Wolff, D.J., Gustashaw, K.M., Zurcher, V., Ko, L., White, W., Weiss, L., Van Dyke, D.L., Schwartz, S., Willard, H.F. Hum. Genet. (1997) [Pubmed]
Annotations and hyperlinks in this abstract are from individual authors of WikiGenes or automatically generated by the WikiGenes Data Mining Engine. The abstract is from MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.About WikiGenesOpen Access LicencePrivacy PolicyTerms of Useapsburg
