M-FISH applications in clinical genetics.

Until recently, presence of de novo marker or derivative chromosomes was quite problematic for genetic counseling especially in prenatal diagnosis, because characterization of marker and derivative chromosomes by conventional cytogenetic techniques was nearly impossible. However, recently developed molecular cytogenetic technique named Multicolor Fluorescence in Situ Hybridization (M-FISH) which paints all human chromosomes in 24 different colors allows us to characterize marker and derivative chromosomes in a single hybridization. In this study, we applied M-FISH to determine the origin of 3 marker and 3 derivative chromosomes. Marker chromosomes were found to originate from chromosome 15 in two postnatal and one prenatal case. Of these, one of the postnatal cases displayed clinical findings of inv dup (115) syndrome and the other of infertility, and the prenatal case went through amniocentesis due to the triple test results. Karyotypes of the patients with derivative chromosomes were designated as 46,XY,der (21)t(1;21)(q32;p11), 46,XX,der(8)t(8;9)(p23;p22) and 46,XX,der(18)t(18;20)(q32;p11.2) according to cytogenetic and M-FISH studies. All of the M-FISH results were confirmed with locus specific or whole chromosome painting probes. The case with der (8)t(8;9) had trisomy 9(p22-pter) and monosomy 8(p23-pter) due to this derivative chromosome. The case with der(18)t(18;20) had trisomy 20(p11.2-pter) and monosomy 18(q32-qter). Parental origins of the derivative chromosomes were analyzed using microsatellite markers located in the trisomic chromosomal segments. Patients' clinical findings were compared with the literature.

Subtelomeric chromosomal rearrangements detected in patients with idiopathic mental retardation and dysmorphic features.

Subtelomeric chromosomal rearrangements detected in patients with idiopathic mental retardation and dysmorphic features: Cryptic aberrations involving the subtelomeric regions of chromosomes are thought to be responsible for idiopathic mental retardation (MR) and multiple congenital anomalies, although the exact incidence of these aberrations is still unclear. With the advent of chromosome-specific telomeric Fluorescence In Situ Hybridization (FISH) probes, it is now possible to identify submicroscopic rearrangements of distal ends of the chromosomes that can not be detected by conventional cytogenetic methods. In this study, cryptic subtelomeric chromosomal aberrations were detected in two of ten patients with idiopathic MR and dysmorphic features by using FISH probes of subtelomeric regions of all chromosome arms. A cryptic unbalanced de novo translocation was detected between the subtelomeric regions of the chromosome 10p and 18p in a patient with severe mental retardation, sensorineuronal deafness and several dysmorphic features. In the other patient, with mild mental retardation and dysmorphic features, a de novo subtelomeric deletion of chromosome 2q was found. In conclusion, in both familial and sporadic cases with idiopathic MR and dysmorphic features, the detection of chromosomal aberrations including subtelomeric rearrangements is of great importance in offering genetic counseling and prenatal diagnosis.

A case with de novo interstitial deletion of chromosome 7q21.1-q22.

A case with de novo interstitial deletion of chromosome 7q21.1-q22: A patient with multiple congenital anomalies was found to have a de novo proximal interstitial deletion of chromosome 7q21.1-q22. The patient was 10.5 years of age, and manifestations include growth retardation (below 3rd percentile), mental retardation, mild microcephaly, hypersensitivity to noise, mild spasticity, short palpebral fissures, alternant exotropia, compensated hypermetropic astigmatism, hypotelorism, hypoplastic labia majora and minora, clinodactyly of fingers 4 and 5. Molecular studies revealed that the deletion had a paternal origin, while chromosomes of both parents cytogenetically were shown to be normal. Molecular, and fluorescence in situ hybridization (FISH) analyses confirmed no deletion at the Williams-Beuren Syndrome region. Some of the heterogeneous clinical findings were consistent with previously reported cases of same chromosomal breakpoints.

Molecular analysis of fragile X syndrome in Antalya Province.

BACKGROUND: Detection of the (CGG)n repeats in the FMR1 gene that cause the fragile X syndrome (FXS), has become a milestone for phenotype-genotype correlation in FXS. AIMS: To screen the FMR1 gene CGG repeats in index cases with FXS and their family members in the Antalya Province. SETTING AND DESIGN: This study was prospectively conducted between January 2000 and March 2005 in Department of Medical Biology and Genetics, Faculty of Medicine, Akdeniz University, Antalya. MATERIALS AND METHODS: A series of 132 cases from three hospitals in Antalya Province were studied. All cases were molecularly screened using non-radioactive Expand Long PCR method that was confirmed by Southern blotting. RESULTS: Seventeen out of 132 cases were found to have a full mutation, including three that were mosaic for premutations/full mutations. Of the 132 cases, eight were found to have the premutation size of the CGG repeats. The remaining 107 cases were identified as normal. CONCLUSIONS: Due to premature ovarian failure and Fragile X premutation Tremor/Ataxia Syndrome related with the premutation, the detection of the premutation will provide valuable information both for clinical follow-up and genetic counseling. In conclusion, our data suggest that expansion of CGG repeats in the FMR1 gene can be analyzed by Expand Long PCR, an efficient and non-radioactive method that can be used to monitor the expansion of premutation to full mutation, which would eventually lead to reduce the FXS prevalence.