# MOLECULAR CLONING OF THE FRAGILE X SITE

> **NIH NIH R01** · EMORY UNIVERSITY · 1994 · $251,002

## Abstract

Fragile sites are heritable chromosomal loci that form cytogenetically
evident gaps and/or breaks after specific biochemical induction.  These
loci occur throughout the human genome and occur at widely variable
population frequencies.  The molecular nature of fragile sites and their
biological consequences are poorly understood.  The fragile site mapping to
Xq27.3, referred to as the fragile X site, is the only fragile site
associated with a distinct phenotype, being found among patients and
carriers of Martin-Bell syndrome (or fragile X syndrome).  This X-linked
condition is responsible for the most frequent form of inherited mental
retardation, occurring at frequencies of >1 per 2000 newborns.  It is
unusual among mammalian X-linked loci because the gene is penetrant in ~30%
of the carrier females and there is a relatively high frequency (~20%) of
nonpenetrant carrier males.  The fragile site itself is either the basis of
this syndrome or is tightly linked to the gene(s) responsible.  This
proposal requests continuation support for a project to identify and clone
the DNA responsible for the fragile X site in order to determine the
relationship between the fragile X site and the associated syndrome.  In
addition, improved DNA-based diagnostic techniques will be developed to
allow accurate carrier detection and prenatal diagnosis.  To identify DNA
of the fragile X site, a somatic cell hybrid system was developed that can
monitor chromosome breakage within or near the fragile X site.  A large
series of independent human-hamster hybrids have been isolated that contain
either human Xpter->q27.3->qter with the breakpoints at or very near the
fragile X site.  Since this breakage was found to be much more frequent in
a fragile X chromosome relative to a normal chromosome, it is likely that
the majority of the breakpoints are clustered in the vicinity of the
sequence responsible for the fragile X site.  Using somatic cell hybrid
mapping panels, an increasing large number of probes have been found, by
several laboratories, to map in the vicinity of the fragile X site.  These
probes will be used on Southern analysis of pulsed field gel resolved DNA
of the hybrids with fragile X-associated chromosome breaks.  Those probes
that identify the breakpoints will be used to develop a physical map of
this region, to initiate chromosome jumps and walks toward the breakpoints,
and to identify corresponding YAC clones.  The breakpoint junctions of
these hybrids will be sequenced as will the corresponding regions of normal
and fragile X syndrome genomes.  The region surrounding these breakpoints
will be searched for highly polymorphic loci which will be used for linkage
analysis in both fragile X syndrome and reference families.  Sequences that
represent candidates for the fragile X site, either by breakpoint
clustering, genetic mapping or unusual sequence, will be tested for
fragility and/or instability in biological assays utilizing both mammalian
and yeast cells.  ...

## Key facts

- **NIH application ID:** 2198027
- **Project number:** 5R01HD020521-09
- **Recipient organization:** EMORY UNIVERSITY
- **SAM.gov UEI:** S352L5PJLMP8
- **Principal Investigator:** Stephen T. Warren
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1994
- **Award amount:** $251,002
- **Award type:** 5
- **Project period:** 1986-04-01 → 1996-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/2198027

## Citation

> US National Institutes of Health, RePORTER application 2198027, MOLECULAR CLONING OF THE FRAGILE X SITE (5R01HD020521-09). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/2198027. Licensed CC0.

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