Characterisation of supernumerary chromosomal markers: a study of 13 cases

Marker chromosomes are defined as 'structurally abnormal chromosomes in which no part can be identified' (ISCN 1995). Supernumerary marker chromosomes (SMC) are 'additional markers' whose origin and composition cannot be determined by conventional cytogenetics. Molecular cytogenetic methods are necessary to identify these additional chromosomal markers. In one third, the SMCs are clinically well-defined in the literature, the remaining two thirds present a major problem for genetic counselling in prenatal diagnosis. At present, different molecular cytogenetic methods are used to determine the origin of SMCs. In this work, we studied 13 SMCs detected by RHG-banding, completed by C-banding and/or NOR-staining. 24-color FISH was used as the primary technique when the chromosomal origin was unknown. Targeted FISH procedures with specific probes (whole chromosome painting, centromeric probe, locus-specific identifier, BAC, etc.) were then performed to confirm and/or specify the chromosomal material present in the SMC. Seven SMCs were found to be associated with phenotypic abnormalities. Five derived from autosomes and two from gonosomes; these are: der(12)t(4;12), dic(15), i(18p), r(19), der(22)t(11;22), r(X), and der(Y). Two markers, r(8) and idic(15), were identified during investigations of infertile couples. Three cases seemed to be phenotypically normal. Four were discovered prenatally: r(2) and r(19) referred for elevated maternal serum markers, der(13/21) referred for advanced maternal age. The fourth SMC, der(14/22), was found during familial investigation following the identification of the same marker in an infertile son. The precise characterisation of the SMCs is of utmost importance for genetic counselling, especially in prenatal diagnosis.

Meiotic segregation in spermatozoa of a 45,XY,-14,der(18)t(14;18)(q11;p11.3) translocation carrier: a case report

A 35-year-old male was found to have a 45,XY,-14,der(18)t(14;18)(q11;p11.3) karyotype during the investigations for a couple with infertility for 8 years. Two sperm samples were obtained and analysed in triple fluorescence in situ hybridization (FISH) with the D18Z1 and LSI IGH/BCL2 probes. The frequency of gametes exhibiting a normal or balanced chromosomal equipment was 87.26 and 90.97% in samples 1 and 2, respectively. No statistically significant difference was found between the results of meiotic segregation of both samples. These proportions are close to those observed among Robertsonian translocation carriers. They can probably be explained by the formation of trivalent in cis configuration during meiosis I between the derivative chromosome and the normal chromosomes 14 and 18, as in Robertsonian translocation carriers. These results suggest that the configuration adopted at pachytene strongly determines the segregation mode that will be preferentially followed during anaphase I.

Effects of phlebotomy therapy on cytochrome P450 2e1 activity and oxidative stress markers in dysmetabolic iron overload syndrome: a randomized trial

AIM

To assess the effects of iron removal on cytochrome P450 2E1 activity and oxidative stress in dysmetabolic iron overload syndrome.

METHODS

Forty-eight patients were randomized to phlebotomy therapy consisting of removal of 300-500 mL of blood every 14 days until serum ferritin levels dropped under 100 microg/L or to follow-up without phlebotomy therapy. Cytochrome P450 2E1 activity was measured at baseline and at the end of treatment by using the 6-hydroxychlorzoxazone/chlorzoxazone blood metabolic ratio, 2 h after the intake of 500 mg of chlorzoxazone.

RESULTS

In the treatment group, a mean of 3.9 +/- 1.3 L of blood was removed and serum ferritin levels dropped from 715 +/- 397 to 74 +/- 34 microg/L. Variation of cytochrome P450 2E1 activity was not significantly different between the 2 groups (0.07 +/- 0.26 vs. 0.03 +/- 0.19, P = 0.36). In the treatment group, low-density lipoprotein cholesterol and vitamin E were lowered after treatment compared with control group (-0.15 +/- 0.51 vs. 0.24 +/- 0.58, P = 0.002 and -1.3 +/- 4.4 vs. 2.3 +/- 5.2, P = 0.03, respectively). Inversely, vitamin C was increased (0.5 +/- 3.5 vs. -1.8 +/- 3.9, P = 0.03).

CONCLUSIONS

In dysmetabolic iron overload syndrome, reduction of iron stores does not significantly influence cytochrome P450 2E1 activity but is associated with a significant decrease of low-density lipoprotein cholesterol, suggesting that venesection therapy may be a suitable option in these patients.

Longitudinal evaluation of a fibrosis index combining MMP-1 and PIIINP compared with MMP-9, TIMP-1 and hyaluronic acid in patients with chronic hepatitis C treated by interferon-alpha and ribavirin

We have recently described a fibrosis index combining serum procollagen type III N-terminal peptide (PIIINP) and matrix metalloproteinase 1 (MMP-1) concentrations for evaluating the amount of liver fibrosis in chronic hepatitis C patients. The aims of the present study were to validate this score in another cohort of patients and to assess its variations along those of TIMP-1, hyaluronic acid (HA) and MMP-9 during antiviral treatment. Seventy-nine patients treated by interferon-alpha and ribavirin for 24 or 48 weeks were included. A liver biopsy was performed within the 6 months before the start of treatment. Serum markers were measured in serum collected the day of the liver biopsy, at start of treatment, and every 3 months during treatment and a 6-month follow-up period. The PIIINP/MMP-1 index was significantly correlated to the METAVIR fibrosis (r = 0.68, P < 0.001). Its overall diagnostic value defined by the area under the receiver operating characteristics curves was 0.77 for discriminating F1 vs F2F3F4, and 0.81 for discriminating F1F2 vs F3F4, and was better than that observed for HA and TIMP-1. At the end of follow-up, the PIIINP/MMP-1 index significantly decreased in responders and remained stable in nonresponder patients. This decrease occurred early and continued regularly during the treatment period. This variation was because of both a decrease of PIIINP and an increase of MMP-1 concentrations. HA and TIMP-1 serum concentrations were also significantly lower at the end of follow-up in responder patients, but early changes were minimal and not influenced by the response to treatment. Our study shows that a noninvasive index combining PIIINP and MMP-1 is a useful tool to follow-up fibrosis change during and after antiviral therapy chronic hepatitis C patients.

Mitochondrial biochemical activities and heteroplasmy evolution in established D. subobscura cell line

A mutant strain of drosophila (D. subobscura) has two types of mitochondrial genomes: a small population (20%) identical to that of the wild strain (15.9 kb) and a predominant population (80%) which has undergone a 5-kb deletion affecting more than 30% of the coding zone. Two cell lines were established from homogenates of embryos from mutant and wild strains. The activities of the respiratory complexes measured in the different cell lines are much lower than in the flies, indicating a glycolytic metabolism. Various modifications of the medium composition did not change this metabolic pathway. The mutant cell line has two types of populations of mitochondrial genomes and the heteroplasmy is equivalent to that measured in the mutant strain. However, the biochemical characteristics differ from those observed in the flies (i.e., the decrease of complex I and III activities), and the various systems of compensation for the consequences of the deletion that are showed in the mutant strain are no longer observed. Furthermore, in contrast with observations made on mutant flies, the heteroplasmy appears unstable in the mutant cell lines: after 60 or so generations, it progressively decreases until it disappears completely. The limited importance of mitochondrial energy metabolism in cells may explain the low impact of the mutation on the established cell line, in contrast to what is seen in the mutant strain.

Meiotic segregation analysis in spermatozoa of pericentric inversion carriers using fluorescence in-situ hybridization

BACKGROUND

Pericentric inversions are structural chromosomal abnormalities resulting from two breaks, one on either side of the centromere, within the same chromosome, followed by 180 degrees rotation and reunion of the inverted segment. They can perturb spermatogenesis and lead to the production of unbalanced gametes through the formation of an inversion loop.

METHODS

We report here the analysis of the meiotic segregation in spermatozoa from six pericentric inversion carriers by multicolour fluorescence in-situ hybridization (FISH) and review the literature.

RESULTS

The frequencies of the non-recombinant products (inversion or normal chromosomes) were 80% for the inv(20), 91.41% for the inv(12), 99.43% for the inv(2), 68.12% for the inv(1), 97% for the inv(8)(p12q21) and 60.94% for the inv(8)(p12q24.1). The meiotic segregation of 20 pericentric inversions (including ours) is now available. The frequency of unbalanced spermatozoa varies from 0 to 37.85%. The probability of a crossover within the inverted segment is affected by the chromosome and region involved, the length of the inverted segment and the location of the breakpoints.

CONCLUSIONS

No recombinant chromosomes were produced when the inverted segment involved <30% of the chromosome length (independent of the size of the inverted segment). Between 30 and 50%, few recombinant chromosomes were produced, inducing a slightly increased risk of aneusomy of recombination in the offspring. The risk of aneusomy became very important when the inverted segment was >50% of the chromosome length. Studies on spermatozoa from inversion carriers help in the comprehension of the mechanisms of meiotic segregation. They should be integrated in the genetic exploration of the infertile men to give them a personalized risk assessment of unbalanced spermatozoa.

Segregation of chromosomes in sperm of Robertsonian translocation carriers

Robertsonian translocations are the most frequent structural chromosomal abnormalities in humans and can affect fertility, with various degrees of sperm alterations in men; or the pregnancy outcome of the carriers. The studies on meiotic segregation of chromosomes in sperm of Robertsonian translocation males find a majority of normal or balanced spermatozoa for the chromosomes related to the translocation (mean 85.42%; range 60-96.60%). Furthermore, recent studies suggest an interchromosomal effect. Studies on spermatozoa from translocation carriers, and in mouse models help the comprehension of the meiotic segregation mechanisms. Results of meiotic segregation analysis in man could be integrated in genetic counselling especially when assisted reproductive technology is required.

Prenatal diagnosis of a mosaic 45,X/46,X,r(X)46,XX with a small ring of the X chromosome

We report the prenatal diagnosis of a mosaic 45,X/46,X,r(X)/46,XX foetus after amniocentesis for maternal second-trimester serum screening. Biparental contribution for the X chromosomes suggest the postzygotic formation of the X ring. The ring is tiny but contains the X-inactive-specific transcript gene (XIST). However, we could not determine whether XIST was correctly expressed or not. The foetal ultrasound examination at 21, 25, 31 weeks' gestation showed no physical abnormalities, prompting the parents to continue the pregnancy. Physical examination at one year-old revealed normal growth and psychomotor development. Only three cases exhibiting an identical 45,X/46,X,r(X)/46,XX mosaicism, but detected postnatally, are reported in the literature. This is the first reported case ofa mosaic 45,X/46,X,r(X)/46,XX identified in the prenatal period.

Interchromosomal effect in sperm of males with translocations: report of 6 cases and review of the literature

Somatic chromosomal abnormalities are frequently found in infertile men, particularly in those with low sperm count and/or seeking intracytoplasmic sperm injection. These abnormalities mostly consist of numerical sex chromosome abnormalities and translocations (Robertsonian or reciprocal). In this study, we searched for the occurrence of non-disjunction of chromosomes not involved in translocations during meiosis, phenomenon called interchromosomal effect (ICE) and first described by Lejeune (1965). Ejaculate samples of two patients carrying a Robertsonian translocation and four a reciprocal translocation patients and four controls (men with a 46,XY karyotype and normal sperm parameters) were studied in dual FISH 7-9, dual FISH 13-21 and triple FISH X-Y-18. A statistically significant increase of disomy X, Y and XY (P = 0.009, P = 0.004, P < 0.001) was found in the Robertsonian der(13;14)(q10;q10) carrier but not in the der(14;21)(q10;q10) carrier compared with controls. Among reciprocal translocation carriers, a significant increase of disomy 21 (P = 0.033) was observed in a sole patient with a t(9;22)(q21;q11.2). The increase of meiotic non-disjunction for chromosome 21 and sex chromosomes is a recurrent event found in other studies. According to our results and published data, the ICE on some specific chromosomes is likely in men carrier of a translocation, although it cannot be excluded that the aneuploidy is related to the oligoasthenoteratozoospermia usually present in these men. Moreover, this phenomenon showed interindividual variations which cannot be predicted. The risk of aneuploidy in sperm of males used for ICSI need to be evaluated. It could be superadded to that of meiotic segregation of the translocation to give a more precise and personalized risk assessment of aneuploidy in the offspring of those men.

Detection of an unexpected subtelomeric 15q26.2 --> qter deletion in a little girl: clinical and cytogenetic studies

Unlike the small proximal 15q deletions causing Prader-Willi and/or Angelman syndrome, distal deletions of the terminal long arm of chromosome 15 have rarely been described. To the best of our knowledge, only four patients with a pure terminal 15q deletion have been documented in the literature. We report here on an unexpected abnormal hybridization pattern for the 15q specific subtelomeric control probe (clone 154P1) of the commercial SNRPN probe in a girl referred for suspicion of Angelman syndrome. Investigation by fluorescent in situ hybridization (FISH) using bacterial artificial chromosome (BAC) clones defined a partial monosomy 15q26.2 --> 15qter for a minimal critical region of approximately 5.7 Mb, which is the most distal de novo 15qter deletion reported to date. All the de novo 15qter deletion cases, including ours, presented with pre- and post-natal growth retardation related to the loss of one copy of the IGF1R gene. Based on the comparaison with the previous published cases and owing to the clinical phenotype of our patient, we define a new subtelomeric 15qter syndrome which would be characterized by intrauterine growth retardation and global post-natal growth failure, variable mental retardation, facial anomalies including relative micrognathia and triangular facies and minor malformations of the extremities including proximally placed thumbs, cubitus valgus, and brachydactyly with tappering of the digits.

Molecular cytogenetic characterization of two small chromosome 8 derived supernumerary mosaic markers

Two small supernumerary mosaic marker chromosomes (SMC) were identified by conventional cytogenetics, one prenatally, the other postnatally. Fluorescence in situ hybridization (FISH) techniques, including 24-color FISH, were applied to identify both SMCs and better characterize their constitution. Patient 1: a 29 year-old man, whose wife had a spontaneous abortion, was found to have a small ring of the pericentromeric region of chromosome 8 (47,XY,+r(8)(p11q11)/46,XY). Patient 2: a 37 year-old woman had amniocentesis. The fetus was found to have a SMC; its presence was confirmed postnatally. Several FISH techniques (24-color, whole chromosome paints, centromeres, telomeres, band 8p22) led to the identification of a small analphoid marker. The marker was an inversion-duplication for part of the short arm of chromosome 8 (47,XY,+inv dup (8)(p23pter)/46,XY). The 24-color FISH allowed us to conclude that both markers originated exclusively from chromosome 8. However, the structure and content of the markers were elucidated using other molecular cytogenetic techniques, showing their complementarity.

Lack of intraindividual variation of unbalanced spermatozoa frequencies from a 46,XY,t(9;22)(q21;q11.2) carrier: Case report

The meiotic segregation pattern of 83 men carrying a balanced reciprocal translocation between two autosomes has already been published. Nevertheless, the question of intraindividual variations has not been addressed yet. A 32-year-old patient was found to be a carrier of a t(9;22)(q21;q11.2) during the investigations for a couple with infertility for 3 years. Two sperm samples were obtained at more than 3 months interval. Both sperm samples were analyzed in triple FISH with the D9Z1 and LSI BCR/ABL ES translocation probes. The frequency of gametes exhibiting a chromosomal imbalance was 45.32% and 42.1% in samples 1 and 2, respectively, with the unbalanced spermatozoa resulting from adjacent 1, adjacent 2, and 3:1 segregation in decreasing frequencies. No statistically significant difference was found between both segregation profiles. Four studies have analyzed the meiotic segregation pattern of translocations within families; they found similar profiles of meiotic segregation in each family, but not between families. This suggests, along with our results, that meiotic segregation is not a random process. More studies on intraindividual variations are necessary to allow a better understanding of the meiotic behaviour of chromosomal rearrangements and the practical interest of studies of this kind.

Chromosome aneuploidy in the spermatozoa of two men with globozoospermia

The objective of this study was to determine the aneuploidy level in spermatozoa in two men with globozoospermia. Sperm nuclei were analysed by fluorescence in-situ hybridization (FISH) in two infertile males with globozoospermia. Dual FISH for chromosomes 7 and 9, 13 and 21, and triple FISH for chromosomes X, Y, and 18 was performed. The main outcome measured was meiotic segregation differences between both globozoospermic men and controls. A statistically significant difference in disomies 13 and 21 was found between patients 1 and 2. The diploidy rate of spermatozoa of patient 1 (0.876%) was significantly increased compared with that of patient 2 (0.304%) and control men (0.293%). In conclusion there seems to be a slightly increased frequency of aneuploidy in round-headed spermatozoa. However, it is unlikely that these aneuploid spermatozoa would be used in assisted reproduction techniques.

Chromosomal abnormalities in couples undergoing intracytoplasmic sperm injection. A study of 370 couples and review of the literature

Intracytoplasmic sperm injection (ICSI) is now widely acknowledged as the most effective therapeutic approach to severe male infertility or unsuccessful in vitro fertilization. Cytogenetic investigations were performed in 370 females and 335 males prior to ICSI between January 1997 and April 2003. Nine men (2.7%) and 48 women (13%) had an abnormal karyotype, 44 females having some degree of numerical sex chromosome mosaicism. A review of the literature showed the prevalence of all types of chromosomal abnormalities to be much higher among male and female partners of couples examined prior to ICSI than among newborns. As most ICSIs are performed with ejaculated spermatozoa from oligospermic men, the distribution and the prevalence of the several types of chromosomal abnormalities are closer to those of oligospermic rather than azoospermic males. Our results combined with those of the literature stress the importance of karyotyping both male and female partners before ICSI is started. Adequate genetic counselling, possibly followed by prenatal diagnosis, should be offered if a chromosomal anomaly is detected.