Unmasking an autosomal recessive disorder by a deletion in the DiGeorge/Velo-cardio-facial chromosome region (DGCR) in 22q11.2
- Children`s Hospital of Philadelphia, PA (United States); and others
Unmasking an autosomal recessive disorder by constitutional hemizygosity is well documented for the embryonal tumors RB and WAGR, where the second hit is a somatic event. Few deletion-mediated recessive conditions have been reported in patients with germline mutations. The major platelet receptor for von Willebrand factor, Glycoprotein Ib (GpIb), is a complex of two plasma membrane glycoproteins, Ib{alpha} and Ib{beta}, covalently linked by disulfide bonds. Defects in this receptor have been associated with the rare congenital autosomal recessive bleeding disorder, Bernard-Soulier syndrome (BSS). BSS is characterized by prolonged bleeding times, thrombocytopenia and very large platelets. The GpIb{beta} gene has been cloned and we have mapped it within the DGCR. We have identified a patient with phenotypic features of both BSS and VCFS. The patient was referred for 22q11-deletion FISH studies because of a conventricular VSD and mild dysmorphia. FISH with the N25 DiGeorge cosmid demonstrated a deletion in 22q11.2. Western blot analysis of the patient`s platelet proteins demonstrates a complete absence of GpIb{beta}. We suggest that haploinsufficiency for the DGCR in this patient unmasks a mutation in the remaining GpIb{beta} allele, resulting in manifestations of BSS. This mechanism, haploinsufficiency coupled with a mutation of the {open_quotes}normal{close_quotes} chromosome, might explain some of the phenotypic variability seen amongst patients with 22q11.2 microdeletions. These results further suggest that patients with contiguous gene deletion syndromes are at increased risk for autosomal recessive disorders and that they provide the opportunity to {open_quotes}map{close_quotes}disease loci.
- OSTI ID:
- 133656
- Report Number(s):
- CONF-941009--
- Journal Information:
- American Journal of Human Genetics, Journal Name: American Journal of Human Genetics Journal Issue: Suppl.3 Vol. 55; ISSN AJHGAG; ISSN 0002-9297
- Country of Publication:
- United States
- Language:
- English
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BASIC STUDIES
BLOOD PLATELETS
CHROMOSOMAL ABERRATIONS
CONGENITAL MALFORMATIONS
DIAGNOSIS
DNA HYBRIDIZATION
DNA-CLONING
FLUORESCENCE
GENE MUTATIONS
GENES
GENETIC MAPPING
GLYCOPROTEINS
HEMIC DISEASES
HEREDITARY DISEASES
HUMAN CHROMOSOME 22
PATIENTS
PHENOTYPE
RECEPTORS
RECESSIVE MUTATIONS