Retrospective Karyotype Study in Mentally Retarded Patients
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ORIGINAL ARTICLE TEIXEIRA WG ET AL. Retrospective karyotype study in mentally retarded patients WELLCY GONÇALVES TEIXEIRA1, FABIANA KALINA MARQUES2*, MAÍRA CRISTINA MENEZES FREIRE3 1MSc in General and Applied Biology – Laboratory Specialist at Instituto Hermes Pardini, Belo Horizonte, MG, Brazil 2MSc in Genetics – Researcher at Instituto Hermes Pardini, Belo Horizonte, MG, Brazil 3PhD in Genetics – Researcher at Instituto Hermes Pardini, Belo Horizonte, MG, Brazil SUMMARY Objective: To describe the chromosomal alterations in patients with mental re- tardation (MR) using G-banding karyotype analysis. Method: A retrospective study of the results G-banding karyotype analysis of 369 patients investigated for MR was performed. Based on the structural rearrange- ments found, the authors searched all chromosomal regions related with break- points, and these were compared with the literature on MR and databases. Results: 338 (91.6%) normal cases, and 31 (8.4%) with some type of chromosom- Study conducted at Instituto Hermes al abnormality were identified. Among the altered cases, 21 patients (67.8%) were Pardini – Pesquisa & Desenvolvimento, identified with structural chromosomal alterations, nine (29%) with numerical Belo Horizonte, MG, Brazil alterations, and one (3.2%) with numerical and structural alterations. Article received: 10/24/2014 Conclusion: Structural chromosomal abnormalities were observed more frequent- Accepted for publication: 11/4/2014 ly in this study. G-banding karyotyping contributes to the investigation of the *Correspondence: causes of MR, showing that this technique can be useful for initial screening of pa- Address: Avenida das Nações, 2448, Distrito Industrial tients. However, higher resolution techniques such as array based comparative ge- Vespasiano, MG – Brazil nomic hybridization (aCGH) and multiplex ligation-dependent probe amplifica- Postal code: 33200-000 [email protected] tion (MPLA) can detect submicroscopic alterations commonly associated with MR. http://dx.doi.org/10.1590/1806-9282.62.03.262 Keywords: karyotype, intellectual disability, chromosome aberrations. INTRODUCTION In some cases, MR can be categorized as syndromic, According to the definition of classical cytogenetics, the i.e. the child has associated dysmorphic features identi- term aneuploidy corresponds to changes in number of fying a genetic syndrome. However, intellectual disabili- chromosomes, including the presence of an extra copy of ty is extremely heterogeneous, a consequence of the large a particular chromosome (trisomy) or the absence of one number of different syndromes related to MR, which ren- chromosome (monosomy) leading to abnormal karyo- ders accurate diagnosis impossible based only on the clin- type. However, with the advent of new high-resolution ical picture.4 Accurate diagnosis is essential to provide a molecular technologies, new aneuploidy syndromes have specific treatment, to establish a clinical predictor of qual- been identified, including deletions and duplications of ity of life, to educate parents on the characteristics and chromosomal regions.1 Changes in gene dosage result- progression of the syndrome, and finally, to define a re- ing from such deletions and duplications are commonly productive prognosis for the family. related to cases of mental retardation. It is estimated that Many cases of MR resulting from duplication and re- over 15% of cases of severe mental retardation are due to current deletions were initially identified by convention- microscopic cytogenetic abnormalities.2 al microscopy techniques or banding. G-banding karyo- Mental retardation (MR), ethically accepted as intellec- type analysis is a technique used to identify individual tual retardation or cognitive delay, is characterized by sig- human chromosomes in many laboratories. This tech- nificant limitations in intellectual functions and adaptive nique, also known as GTG (G-bands by trypsin using Gi- behavior of an individual, with onset of symptoms before emsa), is based on chromosomes digestion with proteo- the age of 18 years. Adaptive behavior refers to adaptive con- lytic enzymes, which are then stained with Giemsa. After ceptual, social and practical skills, while intellectual func- staining, each pair of chromosomes exhibits a character- tions are often measured using intelligence test instruments istic pattern of light and dark bands (G bands), which that generate an intelligence quotient (IQ).2,3 can be individually differentiated under a microscope. 262 REV ASSOC MED BRAS 2016; 62(3):262-268 RETROSPECTIVE KARYOTYPE STUDY IN MENTALLY RETARDED PATIENTS Knowing the importance of accurate diagnosis of MR, for public consultation on the international computer and being aware of the extensive clinical use of G-band- network were used, such as the Mapviewer-National Cen- ing as an important method of diagnosis, this study aimed ter for Biotechonology Information.72 Then, all the spe- to carry out a retrospective analysis of all the results of cific chromosomal regions were researched in the scien- G-banding karyotyping of patients with MR, performed tific literature as to their association with MR. in 2009 at Instituto Hermes Pardini, Sector of Human Cytogenetics, in Belo Horizonte, Minas Gerais, Brazil. RESULTS During 2009, we evaluated the karyotyping results of 369 METHOD patients with MR, of which 143 (38.8%) were female, and The present study followed the guidelines of the Brazil- 226 (61.2%) were male. For most of the patients, 338 ian National Health Council – CNS Resolution 196/96, (91.6%), karyotypes were compatible with normality, while and the identity of all patients was kept confidential. Chro- 31 (8.4%) cases had some type of chromosomal abnor- mosome study was conducted at the Laboratory of Cyto- mality. Of this total of 31 altered cases, 21 patients (67.8%) genetics of Instituto Hermes Pardini using G-banding were identified with structural alterations, 9 (29%) with karyotype analysis. numerical abnormalities, and 1 (3.2%) with numerical For each patient, peripheral blood was collected in and structural alterations (Figure 1). heparin and from these samples cell cultures were pre- Among the patients with identified numerical chro- pared. The cell cultures were treated with colchicine and mosomal abnormalities, five cases had aneuploidy of sex subjected to hypotonic shock. Then, they were fixed on chromosomes: four cases of 47,XXY karyotype, and one slides for subsequent staining of G-bands with trypsin case of X monosomy (45,X karyotype). Regarding auto- and Giemsa. somal chromosomes, three cases of free trisomy 21 Slides evaluation was performed using a microscope (47,XX,+21 karyotype) were detected. The case of numer- (NIKON®, model E 400) coupled to the karyotype analy- ical and structural alteration corresponded to a sis software (Applied Spectral Imaging®, version 6.0). 47,XXY,dup(18)(p12.2 p12.3) karyotype. Karyotypes were described according to the standards As for structural chromosomal abnormalities, recip- present in the 2013 International System for Human Cy- rocal translocations, inversions, deletions, additional chro- togenetic Nomenclature (ISCN).5 mosomal segments, and insertions were observed. Based A survey of karyotyping results was carried out, in- on the comparison of results of karyotypes with structur- cluding types of rearrangements, chromosomal region, al alterations and their specific chromosomal regions, we the possible genes involved, and MR syndromes associ- were able to identify breakpoints involving 1p22.3; 2p24; ated. Based on the structural rearrangements found, we 2q22; 3p13; 3q26.2; 3q12; 5p15.1; 5p15.2; 5p15.3; 6q25.3; searched all chromosomal regions related with break- 7p14; 8p23.1; 8q11.2; 9p24; 10q26.3; 11q23.3; 11q21; points, which were then compared with the literature on 12q24.31; 15q25; 15q26; 17p11.2; 17q21; 18p11.1; 18p11.32; MR. For this comparison, renowned databases available 20q11.2; 22q13. The respective rearrangements as well as Normal Structural alteration Numerical alteration Numerical and structural alteration FIGURE 1 Distribution of results of 369 patients who underwent G-banding karyotyping for investigation of mental retardation in 2009 at Instituto Hermes Pardini. REV ASSOC MED BRAS 2016; 62(3):262-268 263 TEIXEIRA WG ET AL. the correlation between the genes involved and syndromes The only numerical alteration of autosomal chromo- related with MR are shown in Table 1. With the exception some found in this study was trisomy 21 (47,XX,+21). of the deletion on the short arm of chromosome 5 This chromosome constitution is observed in patients [46,XX,del(5)(p11.2) karyotype], found in three cases, all with Down syndrome, an example of neurogenetic disor- other changes occurred once in this study. der related to aneuploidy,1 and corresponds to the most Considering the structural alterations, three cases re- common genetic cause of moderate mental retardation11,12 vealed additional marker chromosomes of unknown or- and intellectual disability.13 igin, two of which were mosaic marker chromosomes. The In this study we also identified three cases of addition- cases of mosaic presented 47,XX,+mar[13]/46,XX[17] al marker chromosomes, two with mosaic karyotype karyotype (mosaicism for one lineage with presence of an (47,XX,+mar[13]/46,XX[17] and 47,XY,+r[8]/46,XY[22]). additional marker chromosome, and another lineage with Supernumerary marker chromosomes are a heterogeneous normal complement) and 47,XY,+r[8]/46,XY[22] karyo- group of structurally