ABSTRACT
Approximately 98% of Prader-Willi syndrome (PWS) and 80% of Angelman syndrome (AS) cases have deletions at a common region in chromosome 15q11-13, uniparental disomy for chromosomes 15 (UPD15), or mutations affecting gene expression in this region. The resulting clinical phenotype (PWS or AS) in each class of mutation depends upon the parent of origin. Both disorders are characterised at the molecular level by abnormal methylation of imprinted genes at 15q11-q13 including the small nuclear ribonucleoprotein N gene (SNRPN). Current diagnostic strategies include high resolution cytogenetics, fluorescence in situ hybridisation (FISH), Southern blot hybridisation, or microsatellite typing. We have developed a novel and rapid diagnostic test for PWS and AS based on differential digestion of expressed (paternally imprinted) SNRPN sequences by the methylation sensitive endonuclease NotI or repressed (maternally imprinted) SNRPN sequences by the methylation requiring nuclease McrBC, followed by PCR amplification of the SNRPN promoter. We have evaluated this test by blinded analysis of 60 characterised DNA samples (20 PWS, 20 AS, and 20 unaffected controls). SNRPN sequences could not be amplified from PWS patient DNA which had been digested with McrBC, nor from AS patient DNA which had been digested with NotI. We were able to make a correct diagnosis of PWS, AS, or unaffected in all 60 samples tested. This novel test is rapid and has a high specificity and sensitivity for deletion and UPD15 cases. These features make this new test suitable as the initial step in a molecular diagnostic strategy for PWS/AS.
Subject(s)
Angelman Syndrome/diagnosis , Autoantigens/genetics , Chromosomes, Human, Pair 15 , Polymerase Chain Reaction/methods , Prader-Willi Syndrome/diagnosis , Adolescent , Adult , Angelman Syndrome/genetics , Blotting, Southern , Child , Child, Preschool , Chromosome Deletion , Diagnosis, Differential , Female , Genomic Imprinting , Humans , In Situ Hybridization, Fluorescence , Infant , Male , Microsatellite Repeats , Middle Aged , Prader-Willi Syndrome/genetics , Ribonucleoproteins, Small Nuclear/genetics , snRNP Core ProteinsABSTRACT
To date, 32 cases of partial 7p monosomy have been described, 14 of which have been associated with craniosynostosis (CRS). There is considerable variation in the size and location of the deleted segment. However, CRS appears to be consistently associated with either a deletion or partial deletion 7p21-->7p22 or more rarely a deletion of 7p13-->7p14. Analysis of a panel of six 7p deletion cases (three with CRS) was undertaken using informative DNA probes, in order to characterize and define the extent of the deletions at the molecular level. There were five de novo deletions and one resulting from the unbalanced product of a paternal balanced insertion. The putative proximal CRS locus at 7p13-->7p14 does not appear to be allelic with Greig cephalopolysyndactyly syndrome. Three probe positions have been refined: pJ5.11 (D7S10) previously mapped to 7p14-->pter does not appear to map proximal to p15; TM102L (D7S135) does not map distal to p22; CRI-P137 (D7S65) maps distal to 7p13.
Subject(s)
Chromosome Deletion , Chromosomes, Human, Pair 7 , Craniosynostoses/genetics , Syndactyly/genetics , Chromosome Banding , Deoxyribonuclease HpaII , Deoxyribonucleases, Type II Site-Specific , Female , Humans , Male , Polymorphism, Restriction Fragment Length , Restriction Mapping , Skull/abnormalities , SyndromeABSTRACT
Craniosynostosis or premature closure of the cranial sutures is a common abnormality occurring in about 1 in 2500 children. There is evidence of mendelian inheritance in some 20% of cases. Published reports of patients with structural alterations of the short arm of chromosome 7 have suggested that two or more genes for craniosynostosis may be situated in this region. The Saethre-Chotzen syndrome (acrocephalosyndactyly type III) is one of the most common autosomal dominant craniosynostosis syndromes. Results of molecular genetic linkage studies provide evidence for localisation of the gene responsible to distal chromosome 7p.
Subject(s)
Acrocephalosyndactylia/genetics , Chromosomes, Human, Pair 7 , Genes, Dominant/genetics , Genetic Linkage/genetics , Chromosome Mapping , DNA Probes/genetics , Female , Humans , Male , PedigreeABSTRACT
Acrocallosal syndrome is an autosomal recessive form of polysyndactyly associated with mental retardation and agenesis of the corpus callosum. There have been suggestions that it is allelic to the Greig cephalopolysyndactyly syndrome. Linkage analysis, using flanking markers, shows this suggestion is unlikely to be correct.
