GENETIC RESEARCH

PROJECT OF STUDY ON THE ABERRATIONS OF CHROMOSOME 14 PHASE 2 YEAR 2007

Institue of Medical Genetic
Università Cattolica Sacro Cuore
L.go F. Vito, 1
00168 Roma

The “Microarray-CGH” tecnique has the target to individuate quantitative chromosomic anomalies (deletions or partial duplications) of dimensions inferior to the limits of resolution of a conventional chromosomic test and for that defined “criptical”.

Quantitative chromosomic anomalies are responsible of the 20-30% of cases of mental retardation. We must state that also in the presence of a chromosomic anomaly already evidenced through a standard chromosomic test, the chromosomic re-arrangement can be more complex. Multiple quantitative anomalies can affect the final phenotype. In the specific case of Ring 14 syndrome, there is evidence of some ring cases associated not only to partial loss of the terminal region of the long arm, but also to partial duplications of nearer regions.

“Microarray-CGH” tecnique is based on the following principles:

• DNA extraction from peripheric blood of the examined subject
• That DNA must be firstly hybridized with control DNA, in equimolecular quantities. The DNA in examination and the control DNA are marked with two different fluorinchromes, for instance red for the DNA in examination and green for the control DNA. If the DNA in examination has neither losses nor duplications, hybridization between the two DNA is complete and in some way the two DNA humble themselves. If, viceversa, the DNA in examination has a deletion, it exceeds for that specific reason the control DNA; analogously, if the DNA in examination has a duplication it exceeds, for that reason, the DNA in examination.
• Upon reciprocal hybridization, the two DNA are then hybridized by a series of molecular probes placed on the same slide. Molecular probes are selected in a way to cover the complete human genoma, at a distance of 1 Mb or less, according to the resolution degree chosen. If hybridization between the control DNA and the DNA in examination is complete (because there is neither deletions nor duplications) we obtain an unbroken line, elaborated by a specific software; if viceversa in the DNA in examination there is present a deletion or a duplication, we obtain a deviation respectively in favour of the control DNA or of the DNA in examination . The observed deviation is limited to the region interested by the re-arrangement and gives simultaneously information on the extension of the chromosomic defect and on the genes interested by the anomaly.

Chromosome 14 anomalies STUDY PROJECT

Principal investigator: Giovanni Neri
Co-principal investigator: Marcella Zollino
Duration of the project: 4 years
Begun in 2003

Istituto di Genetica Medica,
Università Cattolica Sacro Cuore, L.go F. Vito, 1
00168 Roma

“Ring Chromosome 14” syndrome and deletion of chromosome 14, is a genetic condition characterized by multiple congenital anomalies and psychomotor delay. It is caused by partial loss of genetic material from the long arm of chromosome 14. The most frequent signs and symptoms are psychomotor delay, a particular aspect of the face, epilepsy and retinitis pigmentosa. Clinical manifestations vary from patient to patient, also in relation to the instability of the ring which can result in somatic mosaicism. One should also take into account the fact that chromosome 14 is subjected to imprinting in man, so that some of its regions may be differently active according to parent of origin.

We have planned a study of the genotype-phenotype correlations in patients with aberrations of chromosome 14, which will proceed as follows:

• analysis of the karyotype on 100 peripheral blood cells, to be repeated every two years, to verify the level of mosaicism and its evolution with time. In the case of definite mosaicism in blood, analysis of the karyotype will be extended to 100 skin fibroblasts, at least in those patients who accept to undergo a skin biopsy. Skin biopsy is a minimally invasive procedure, performed under local anesthesia.
• assessment of the parental origin of the rearranged chromosome 14 through microsatellite analysis, which requires a blood sample also from the parents.
• definition, with molecular cytogenetic techniques, of the deleted chromsomal segment in each single patient.

• preparation of lymphoblastoid cell lines from each family (patient and both parents);
• conventional chromosomal testing with an average resolution of 550 bands;
• fluorescent in situ hybridation (FISH) with specific BACs for the distal half of the long arm of chromosome 14 with an average distance of 500-800 kb;
• segregation analysis of DNA polymorphisms (microsatellites) amplified with PCR; e) clinical assessment of patients and correlation of their phenotypes with the corresponding genetic defect.

Documents

› Letter for families (87 KB)
› Letter for doctors (86 KB)