Detailed analysis of 22q11.2 with a high density MLPA probe set

The presence of chromosome-specific low-copy repeats (LCRs) predisposes chromosome 22 to deletions and duplications. The current diagnostic procedure for detecting aberrations at 22q11.2 is chromosomal analysis coupled with fluorescence in situ hybridization (FISH) or PCR-based multiplex ligation dependent probe amplification (MLPA). However, there are copy number variations (CNVs) in 22q11.2 that are only detected by high-resolution platforms such as array comparative genomic hybridization (aCGH). We report on development of a high-definition MLPA (MLPA-HD) 22q11 kit that detects copy number changes at 37 loci on the long arm of chromosome 22. These include the 3-Mb region commonly deleted in DiGeorge/velocardiofacial syndrome (DGS/VCFS), the cat eye syndrome (CES) region, and more distal regions in 22q11 that have recently been shown to be deleted. We have used this MLPA-HD probe set to analyze 363 previously well-characterized samples with a variety of different rearrangements at 22q11 and demonstrate that it can detect copy number alterations with high sensitivity and specificity. In addition to detection of the common recurrent deletions associated with DGS/VCFS, variant and novel chromosome 22 aberrations have been detected. These include duplications within as well as deletions distal to this region. Further, the MLPA-HD detects deletion endpoint differences between patients with the common 3-Mb deletion. The MLPA-HD kit is proposed as a cost effective alternative to the currently available detection methods for individuals with features of the 22q11 aberrations. In patients with the relevant phenotypic characteristics, this MLPA-HD probe set could replace FISH for the clinical diagnosis of 22q11.2 deletions and duplications.

Mesenchymal/epithelial induction mediates olfactory pathway formation

In the olfactory pathway, as in the limbs, branchial arches, and heart, mesenchymal/epithelial induction, mediated by retinoic acid (RA), FGF8, sonic hedgehog (shh), and the BMPs, defines patterning, morphogenesis, and differentiation. Neuronal differentiation in the olfactory epithelium and directed growth of axons in the nascent olfactory nerve depend critically upon this inductive interaction. When RA, FGF8, shh, or BMP signaling is disrupted, distinct aspects of olfactory pathway patterning and differentiation are compromised. Thus, a cellular and molecular mechanism that facilitates musculoskeletal and vascular development elsewhere in the embryo has been adapted to guide the differentiation of the olfactory pathway in the developing forebrain.

Cat eye syndrome chromosome breakpoint clustering: identification of two intervals also associated with 22q11 deletion syndrome breakpoints

The supernumerary cat eye syndrome (CES) chromosome is dicentric, containing two copies of 22pter-->q11.2. We have found that the duplication breakpoints are clustered in two intervals. The more proximal, most common interval is the 450-650 kb region between D22S427 and D22S36, which corresponds to the proximal deletion breakpoint interval found in the 22q11 deletion syndrome (DiGeorge/velocardiofacial syndrome). The more distal duplication breakpoint interval falls between CRKL and D22S112, which overlaps with the common distal deletion interval of the 22q11 deletion syndrome. We have therefore classified CES chromosomes into two types based on the location of the two breakpoints required to generate them. The smaller type I CES chromosomes are symmetrical, with both breakpoints located within the proximal interval. The larger type II CES chromosomes are either asymmetrical, with one breakpoint located in each of the two intervals, or symmetrical, with both breakpoints located in the distal interval. The co-localization of the breakpoints of these different syndromes, plus the presence of low-copy repeats adjacent to each interval, suggests the existence of several specific regions of chromosomal instability in 22q11.2 which are involved in the production of both deletions and duplications. Since the phenotype associated with the larger duplication does not appear to be more severe than that of the smaller duplication, determination of the type of CES chromosome does not currently have prognostic value.

Forebrain induction, retinoic acid, and vulnerability to schizophrenia: insights from molecular and genetic analysis in developing mice

Schizophrenia is thought to be a disease of early development that ultimately affects forebrain neurons and circuits. There may be a relationship between disrupted forebrain development; malformations of the limb, face, and heart; and signaling via the steroid-like hormone retinoic acid (RA) in some schizophrenic patients. The limbs, face, heart, and forebrain all develop from sites where neural crest-derived, RA-producing mesenchyme contributes to induction and differentiation of adjacent epithelia. Induction between neural crest-derived, RA-producing mesenchyme, the anterior neural tube, and the anterior surface epithelium of the embryo guides regional differentiation and pathway formation during forebrain development. Furthermore, there are at least two mouse mutations--in the Pax-6 and Gli-3 genes--that cause peripheral malformations and specifically disrupt neural crest mediated, RA-dependent induction and differentiation in the forebrain. These observations suggest that induction might provide a common target for genes that alter morphogenesis of peripheral structures, disrupt RA-signaling, and compromise forebrain development. In the forebrain, some of these disruptions might influence the numbers or cellular properties of neurons and circuits. Such changes might be reflected in the aberrant forebrain function that characterizes schizophrenia.

Measuring functional status in children with genetic impairments

One of the consequences of genetic impairments in early childhood is their long-term effect on children's developmental skills in communication, learning, and adaptive behaviors. Functional assessment provides families and clinicians with a common language for describing a child's strengths and limitations in self-care (feeding, dressing, grooming, bathing, continence), mobility, and communication/social cognition. The National Center for Medical Rehabilitation Research described a model of disablement that includes five dimensions: pathophysiology, impairment, functional limitations, disability, and societal limitations. Using this framework, along with the Functional Independence Measure for children, the WeeFIM(R), we describe functional strengths and challenges in children with Down syndrome, spina bifida, congenital limb anomalies, congenital heart disease, urea cycle disorders, severe multiple developmental disabilities, and DiGeorge malformation sequence. We also briefly describe several pediatric functional/adaptive assessment instruments used by developmental professionals (Battelle Developmental Inventory, Vineland Adaptive Behavior Scales, Amount of Assistance Questionnaire). By tracking functional status, health professionals can prioritize secondary and tertiary prevention strategies that optimize self-care, mobility, communication, and learning. When functional limitations interfere with the acquisition of these essential skills, family and community support programs can be maximized.

Frequency of 22q11 deletions in patients with conotruncal defects

OBJECTIVES

This study was designed to determine the frequency of 22q11 deletions in a large, prospectively ascertained sample of patients with conotruncal defects and to evaluate the deletion frequency when additional cardiac findings are also considered.

BACKGROUND

Chromosome 22q11 deletions are present in the majority of patients with DiGeorge, velocardiofacial and conotruncal anomaly face syndromes in which conotruncal defects are a cardinal feature. Previous studies suggest that a substantial number of patients with congenital heart disease have a 22q11 deletion.

METHODS

Two hundred fifty-one patients with conotruncal defects were prospectively enrolled into the study and screened for the presence of a 22q11 deletion.

RESULTS

Deletions were found in 50.0% with interrupted aortic arch (IAA), 34.5% of patients with truncus arteriosus (TA), and 15.9% with tetralogy of Fallot (TOF). Two of 6 patients with a posterior malalignment type ventricular septal defect (PMVSD) and only 1 of 20 patients with double outlet right ventricle were found to have a 22q11 deletion. None of the 45 patients with transposition of the great arteries had a deletion. The frequency of 22q11 deletions was higher in patients with anomalies of the pulmonary arteries, aortic arch or its major branches as compared to patients with a normal left aortic arch regardless of intracardiac anatomy.

CONCLUSIONS

A substantial proportion of patients with IAA, TA, TOF and PMVSD have a deletion of chromosome 22q11. Deletions are more common in patients with aortic arch or vessel anomalies. These results begin to define guidelines for deletion screening of patients with conotruncal defects.