Molecular analysis of syndromic congenital heart disease using short tandem repeat markers and semiquantitative polymerase chain reaction method

Identification of candidate genes for congenital ventricular septal defects with HSA22q11 loss of heterozygosity

INTRODUCTION AND OBJECTIVES

Ventricular septal defect (VSD) is one of the major forms of congenital heart disease (CHD) in individuals with Homo sapiens chromosome 22q11 (HSA22q11) deletion syndrome. The objective was to identify candidate genes associated with VSD located within HSA22q11 by analyzing loss of heterozygosity (LOH) using microsatellite genotyping and by gene dosage analysis in seven candidate genes.

METHODS

The study involved 82 families with CHD, which included 261 individuals (85 patients and 176 siblings and parents). All were screened for LOH in the HSA22q11 region by microsatellite (n=10) genotyping. Bioinformatic strategies were used to characterize seven candidate genes located within this region in greater detail. Quantitative polymerase chain reaction analysis was used to determine the dosages of the seven candidate genes in 16 patients with LOH of HSA22q11.

RESULTS

Overall, 42 out of 85 patients (49.4%) with CHD had at least one LOH in the HSA22q11 region. Moreover, LOH of HSA22q11 was found in 17 out of 29 patients with a VSD and in three out of four families with two offspring affected by CHD. Dosage analysis of the seven candidate genes showed recurrent heterozygous deletion of HIRA, GNB1L and TUBA8 genes in 16 VSD patients with a LOH of HSA22q11.

CONCLUSIONS

Microsatellite genotyping identified LOH of HSA22q11 in several types of CHD. Heterozygous deletion of HIRA, GNB1L or TUBA8 genes might play an important role in ventricular septum development. Since CHD can be a familial disease, screening the siblings of a proband for LOH of HSA22q could be valuable for early diagnosis and treatment.

New tetranucleotide STRP markers for detecting the 22q11.2 deletion

The 22q11.2 deletion syndrome is the most common microdeletion syndrome mainly characterized by hemizygous deletions and congenital heart defect (CHD). By using polymerase chain reaction (PCR), genotyping of short tandem repeat polymorphic (STRP) markers is a common and powerful means of detecting microdeletion. We have developed five new tetranucleotide repeat markers, 22D_4_1, 22D_4_2, 22D_4_3, 22D_4_4 and D22S873 in the proximal region of 22q11.2 deletion. To ascertain whether these markers could be used reliably in genotyping, we performed genotyping analysis on 200 unrelated individuals from a Chinese Han population and 67 CHD patients and their unaffected parents. Population data showed that the five markers met Hardy-Weinberg expectations and were highly polymorphic. By using the five markers, six of 67 CHD patients were determined to have a deletion within chromosome 22q11.2. Compared with dinucleotide markers, tetranucleotide markers produce weaker stutter bands and have no artificial multiband patterns. PCR amplification results from the five new tetranucleotide STRP markers were unambiguous and easier to interpret in genotyping. This study demonstrated that the five markers were efficient and reliable suggesting that genotyping using tetranucleotide STRP markers is an alterative approach to detect the deletion on chromosome 22q11.2 in clinical diagnosis and for genetic consultation.

Chromosome 22 microdeletion by F.I.S.H. in isolated congenital heart disease

OBJECTIVE

To analyze the frequency of del22q11.2 in non-syndromic CHDs using classical cytogenetics and Fluorescence In Situ Hybridization (FISH) technique in Indian population.

METHODS

105 prospective cases which included 6 families with isolated, non-syndromic cardiac defects were analyzed clinically by a cardiologist and a geneticist. The cases were then subjected to karyotypic (classical cytogenetics) as well as FISH analysis. The efficacy of FISH technique was compared with inference drawn from classical cytogenetics.

RESULTS

Karyotypic analysis of all the 105 patients revealed a normal chromosomal complement. Microdeletion 22q11.2 was observed in six patients (5.71%) by FISH studies. FISH studies were also performed on the parents of these six patients who revealed a normal chromosome 22. No correlation was found between clinical features (mild or unspecific) with 22q11.2 microdeletion.

CONCLUSION

The testing for microdeletion 22q11.2 in isolated non-syndromic patients using FISH technique is mandatory even when mild/unspecific extracardiac abnormalities are seen in the patients.

22q11.2 deletion mosaicism in patients with conotruncal heart defects

BACKGROUND

Some patients with conotruncal heart defects (CTDs) have a chromosome 22q11.2 deletion, but we do not know whether patients with CTDs who are missing the peripheral blood-cell chromosome 22q11.2 deletion are also missing the 22q11.2 deletion in myocardial cells, and whether patients with the 22q11.2 deletion can show a different 22q11.2 deletion in peripheral blood cells and myocardial cells due to a postzygotic mutation during the embryonic period.

METHODS

A total of 32 Chinese pediatric nonsyndromic CTD patients (21 with tetralogy of fallot [TOF], 9 with double outlet right ventricle [DORV], 1 with pulmonary artery atresia with ventricular septal defect [PAA/VSD], and 1 with congenitally corrected transposition of the great arteries [CCTGA]), 12 females and 20 males ranging in age from 5 months to 7 years, were included in our study. We used fluorescence in situ hybridization (FISH) to find the chromosome 22q11.2 deletion in peripheral blood cells and compared genotypes of 15 short tandem repeat (STR) markers within 22q11.2 between peripheral blood cells and myocardial cells to search for genetic mosaicism of the chromosome 22q11.2 deletion.

RESULTS

Three patients, 2 with TOF and 1 with DORV, were determined to have the peripheral blood cell chromosome 22q11.2 deletion. There was no STR genotypic difference observed between peripheral blood cells and myocardial cells in patients with or without the chromosome 22q11.2 deletion.

CONCLUSIONS

Genetic mosaicism may not play a major role in the etiology of isolated CTDs.

Genetic analysis of chromosome 22q11.2 markers in congenital heart disease

Congenital heart disease (CHD) is a common cardiac defect found in infants and children. Despite advances in diagnosis and treatment, our understanding of the causative mechanism and etiology of CHD is limited. To determine the genetic etiology of CHD, we selected 11 consecutive short tandem-repeat polymorphic (STRP) markers located in the interval of the 22q11.2 region to perform genotype analysis on a large number of CHD patients (>120) and their normal relatives (>220). The results show that as regards the distribution of allelic size and frequency of these STRP markers, there were no significant differences between the CHD patients and the normal volunteers. This indicates that there is no linkage disequilibrium with these markers in CHD. In the level of heterozygosity for each marker in nonsyndromic CHD and conotruncal heart defect (CTD), there were no significant differences between the two populations. In syndromic CHD, the level of heterozygosity for D22S1648 was significantly lower than that observed in the unaffected population (chi(2) = 11.25; P = 0.001). This suggests that there may be a deletion at the D22S1648 locus, and the low heterozygosity of D22S1648 indicates that this marker can be used as a genetic marker for detecting microdeletions in 22q11.2. With the use of fluorescence in situ hybridization (FISH) and real-time quantitative polymerase chain reaction (PCR) performed on syndromic patients, we confirmed the molecular results.