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Title: A positional cloning strategy to identify candidate genes for nonsydromic X-linked mental retardation in Xp11.2
Author: Holden, S. T.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2005
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The primary objective of the studies presented here was to identify candidate genes for nonsyndromic X-linked mental retardation (NS-XLMR) in Xp11.2 by molecular characterisation of the Xp11.2 breakpoints in five rare female individuals with balanced X;autosome translocations and mental retardation. The hypothesis underlying this positional cloning strategy was that genes disrupted by the X chromosome breakpoints are candidate genes for NS-XLMR. Five Xp11.2 and three autosomal translocation breakpoints were mapped by fluorescence in situ hybridisation (FISH) using large insert genomic clones generated by the Human Genome Project as probes. In silico analysis of genomic sequences at the X breakpoint loci was used to identify genes potentially disrupted by the translocations. In collaboration with Dr Vera Kalscheuer’s group in Berlin, a putative diacylglycerol kinase XM_066534 was found to be disrupted by a t(X;22), and its involvement in NS-XLMR evaluated. Restriction mapping by southern blot hybridisation analysis was undertaken to fine map the X breakpoints of two translocations, and RT-PCR analysis used to investigate expression of genes at the X breakpoint loci in translocation cell lines. One t(X;16) was found to disrupt expression of the zinc finger gene ZNF81. This is the second example of a balanced X;autosome translocation associated with mental retardation which disrupts this gene, providing further evidence that mutations in ZNF81 cause mental retardation. The X breakpoint of a second t(X;16) was localised to a 9 kb interval between two partial cDNAs. Further work on these sequences led to the cloning and characterisation of two novel genes expressed in brain, WNK3, a putative protein kinase, and CXorf17 and its mouse ortholog, orf34. Characterisation of CXorf17 and orf34 facilitated the identification of a novel, chordate-specific gene family which encodes several putative transmembrane proteins that have no sequence homology to any previously annotated proteins, known functional domains or sequence motifs.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available