This study investigated the phenotypic manifestations of interstitial duplications of chromosome 15 that involve the Prader-Willi/Angelman syndrome critical region (PWACR). Twenty-one affected individuals from six families were evaluated in detail, using standardized and semi-standardized measures of intelligence, psychopathology, and physical anomalies. Special attention was placed on determining the prevalence of autism spectrum disorders as well as the relationship between the parental origin of the duplication and the phenotypic effects. Assessments of the affected individuals were compared with evaluations of the unaffected relatives from the same families. Results indicated that duplications in the region were associated with variable degrees of intellectual impairments and motor coordination problems. Four of the subjects received a diagnosis of pervasive developmental disorder. Three of these cases were probands and only one met criteria for classic autism. There was very little evidence of the duplication cosegregating with autism spectrum disorder diagnosis. Paternally inherited duplications were significantly less likely to give rise to phenotypic effects. The findings indicate that duplications in the PWACR give rise to developmental delay but not necessarily autism spectrum disorders. They also suggest that phenotypic expression is dependent on the parental origin of the duplication and implicate maternally active genes in the pathogenesis of the developmental impairments. Further research will be required to clarify the range and basis of the phenotypic manifestations.
Objective: To describe the systematic analysis of constitutional de novo apparently balanced translocations in patients presenting with abnormal phenotypes, characterise the structural chromosome rearrangements, map the translocation breakpoints, and report detectable genomic imbalances. Methods: DNA microarrays were used with a resolution of 1 Mb for the detailed genome-wide analysis of the patients. Array CGH was used to screen for genomic imbalance and array painting to map chromosome breakpoints rapidly. These two methods facilitate rapid analysis of translocation breakpoints and screening for cryptic chromosome imbalance. Breakpoints of rearrangements were further refined (to the level of spanning clones) using fluorescence in situ hybridisation where appropriate.
We evaluated seven children who had been exposed to sodium valproate (or valproic acid) in utero. A consistent facial phenotype was observed in all seven in addition to other birth defects in four. The facial changes consisted of epicanthal folds which continued inferiorly and laterally to form a crease or groove just under the orbit, flat nasal bridge, small upturned nose, long upper lip with a relatively shallow philtrum, a thin upper vermillion border, and downturned angles of the mouth. Hypospadias, strabismus, and psychomotor delay were found in two males; two children had nystagmus and two had low birth weight.
Chromosome 15 is frequently involved in the formation of structural rearrangements. We report the molecular characterisation of 16 independent interstitial duplications, including those of one individual who carried a duplication on both of her chromosomes 15, and three interstitial triplications of the Prader-Willi/Angelman syndrome critical region (PWACR). In all probands except one, the rearrangement was maternal in origin. In one family, the duplication was paternal in origin, yet appeared to segregate in a sibship of three with an abnormal phenotype that included developmental delay and a behavioural disorder. Ten duplications were familial, five de novo and one unknown. All 16 duplications, including two not visible by routine G-banding, were of an almost uniform size and shared the common deletion breakpoints of Prader-Willi syndrome and Angelman syndrome. Like deletions, the formation of duplications can occur in both male and female meiosis and involve both inter- and intrachromosomal events. This implies that at least some deletions and duplications are the reciprocal products of each other. We observed no instances of meiotic instability in the transmission of a duplication, although recombination within the PWACR occurred in two members of the same family between the normal and the duplicated chromosome 15 homologues. All three triplications arose de novo and included alleles from both maternal chromosomes 15. Triplication breakpoints were more variable and extended distally beyond the PWACR. The molecular characteristics of duplications and triplications suggest that they are formed by different mechanisms.
We report eight females with small deletions of the short arm of the X chromosome, three of whom showed features of autism. Our results suggest that there may be a critical region for autism in females with Xp deletions between the pseudoautosomal boundary and DXS7103. We hypothesise that this effect might be due either to the loss of function of a specific gene within the deleted region or to functional nullisomy resulting from X inactivation of the normal X chromosome.
The cause of mental retardation, present in approximately 3% of the population, is unexplained in the majority of cases. Recent reports have suggested that cryptic telomeric rearrangements resulting in segmental aneuploidy and gene-dosage imbalance might represent a significant cause of idiopathic mental retardation (IMR). Two groups of patients with unexplained developmental delay (unselected and selected) and a group of control individuals have been investigated to determine the frequency of submicroscopic telomeric rearrangements associated with IMR and the frequency within the normal population. In contrast to current thinking, our data have shown that true cryptic telomeric rearrangements are not a significant cause of IMR. No fully cryptic abnormalities were detected in our IMR groups, although a semi-cryptic unbalanced telomeric translocation was identified in one selected patient by high-resolution G-band analysis. This abnormality was confirmed and characterised by fluorescence in situ hybridisation (FISH) with telomere-specific probes. A further 13 cytogenetically detected subtle terminal rearrangements were characterised by using multi-telomere FISH. Seven of these had previously been reported as normal, three of which were shown to be interstitial deletions. These cases illustrate the importance of high-resolution analysis to exclude subtle but cytogenetically visible abnormalities prior to subtelomere FISH screening when determining the frequency of cryptic telomeric rearrangements. Unexpectedly, two cryptic telomeric abnormalities were detected among our control individuals, suggesting that submicroscopic telomeric abnormalities may be a not uncommon finding in the general population. Hence, our data have important implications when defining the significance of cryptic telomeric rearrangements detected during screening programmes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.