Molecular characterization of Spanish patients with MECP2 duplication syndrome

MECP2 duplication syndrome (MDS) is an X-linked neurodevelopmental disorder characterized by a severe to profound intellectual disability, early onset hypotonia and diverse psycho-motor and behavioural features. To date, fewer than 200 cases have been published. We report the clinical and molecular characterization of a Spanish MDS cohort that included 19 boys and 2 girls. Clinical suspicions were confirmed by array comparative genomic hybridization and multiplex ligation-dependent probe amplification (MLPA). Using, a custom in-house MLPA assay, we performed a thorough study of the minimal duplicated region, from which we concluded a complete duplication of both MECP2 and IRAK1 was necessary for a correct MDS diagnosis, as patients with partial MECP2 duplications lacked some typical clinical traits present in other MDS patients. In addition, the duplication location may be related to phenotypic severity. This observation may provide a new approach for genotype-phenotype correlations, and thus more personalized genetic counselling.

A 11.7-Mb Paracentric Inversion in Chromosome 1q Detected in Prenatal Diagnosis Associated with Familial Intellectual Disability

Most apparent balanced chromosomal inversions are usually clinically asymptomatic; however, infertility, miscarriages, and mental retardation have been reported in inversion carriers. We present a small family with a paracentric inversion 1q42.13q43 detected in routine prenatal diagnosis. Molecular cytogenetic methods defined the size of the inversion as 11.7 Mb and excluded other unbalanced chromosomal alterations in the patients. Our findings suggest that intellectual disability is caused by dysfunction, disruption, or position effects of genes located at or near the breakpoints involved in this inversion.

Trisomy 18p caused by a supernumerary marker with a chromosome 13/21 centromere: a possible recurrent chromosome aberration

We present a clinical and molecular cytogenetic characterization of two new patients with a complex supernumerary marker consisting of the entire short arm of chromosome 18 with a chromosome 13/21 centromere. One patient is a girl with a nonsyndromic intellectual disability and the second is a prenatally diagnosed fetus. To our knowledge, these are the fourth and fifth such cases to be described in the literature, suggesting the existence of a possible recurring constitutional structural chromosome abnormality.

Supernumerary ring chromosome: an etiology for Pallister-Killian syndrome?

Characterization of marker chromosomes before the introduction of array CGH (aCGH) assays was only based on their banding patterns (G, C, and NOR staining) and fluorescent in situ hybridization techniques. The use of aCGH greatly improves the identification of marker chromosomes in some cases. We describe an atypical case of Pallister-Killian syndrome (PKS) detected at prenatal diagnosis with a very unusual cytogenetic presentation: a supernumerary ring chromosome including two copies of 12p. A similar anomaly described in a postnatal patient suggests ring chromosome as a possible cause of PKS. Extra ring chromosomes might be a more common etiology for PKS than previously thought, given the difficulty in their characterization before the advent of aCGH.

Hidden mosaicism in patients with Klinefelter's syndrome: implications for genetic reproductive counselling

BACKGROUND

Most individuals with Klinefelter's syndrome (KS) are azoospermic but residual foci of spermatogenesis have been observed in some patients. However, no consistent predictive factors for testicular sperm extraction success have been established and mosaicism could be a factor to investigate. In this study, we have assessed the degree of mosaicism in somatic and germinal tissues in KS, the meiotic competence of 47,XXY germ cells and the aneuploidy rate of post-reductional cells.

METHODS

Five patients with KS previously diagnosed as pure 47,XXY have been studied. Samples from four donors were processed as controls. The chromosome constitution of lymphocytes, buccal mucosa and testicular tissue was assessed by interphase fluorescence in situ hybridization for chromosomes X, Y and 18. In meiotic figures, sex chromosome number and pairing was confirmed.

RESULTS

46,XY cell lines were observed in all patients and tissues analysed. The degree of mosaicism (mean ± SD) differed among tissues (lowest in lymphocytes: 4.8 ± 2.5%; highest in Sertoli cells: 42.3 ± 11.1%). Meiotic figures were found in three cases (KS1, KS2 and KS5), all of them showed an XY complement. Hyperhaploid post-reductional cells were found in all patients (range: 3.3-36.4%) and increased rates versus controls (P< 0.05) were observed.

CONCLUSIONS

Diagnosis of homogeneous KS based on lymphocyte karyotyping should be contrasted in other tissues. Mucosa cells could help to better approximate the degree of germ cell mosaicism. Our results indicate that 47,XXY germ cells are not meiotically competent. Increased post-reductional aneuploidy rate is related to meiotic errors in 46,XY cells. Appropriate genetic counselling is recommended in KS.

Non-mosaic trisomy 20 of paternal origin in chorionic villus and amniotic fluid also detected in fetal blood and other tissues

Trisomy 20 mosaicism is a common abnormality found in prenatal diagnosis. Its clinical significance remains unclear since approximately 90-93% of cases result in normal phenotype. Only 5 cases of non-mosaic trisomy 20 in amniotic fluid culture surviving beyond the first trimester have been reported. Moreover, trisomic cells are generally not detectable in blood and have only been reported in three cases. We present a case of non-mosaic trisomy 20 found in chorionic villi sample and amniotic fluid culture in a fetus with minor abnormalities not detected by ultrasound examination. Pathological examination of the fetus only revealed right pulmonary isomerism and camptodactily, and no major malformations were disclosed. Trisomic lineage was also detected in fetal blood, kidney, skin and brain tissue cultures. Molecular analysis revealed that the extra chromosome 20 was originated in paternal meiosis. To our knowledge, we report the first prenatal case of non-mosaic trisomy 20 of paternal origin that has been confirmed in several fetal tissues, including blood, in a fetus with minor malformations not detected prenatally.

Variegated aneuploidy related to premature centromere division (PCD) is expressed in vivo and is a cancer-prone disease

We present three patients with variegated aneuploidy and premature centromere division (PCD), a rare chromosomal abnormality in humans. Comparison of these three and eight other patients with variegated aneuploidy related to PCD demonstrates a phenotype comprising most frequently microcephaly, CNS anomalies (with cerebellar affection and migration defects), mental retardation, pre-and postnatal growth retardation, flat and broad nasal bridge, apparently low-set ears, eye and skin abnormalities, and ambiguous genitalia in male patients. The occurrence of Wilms tumor in three patients, rhabdomyosarcoma in two others and acute leukemia in a fifth characterizes this condition as a chromosome or genome instability disorder with a high risk of malignancy. FISH studies in uncultured blood and buccal smear cells demonstrate that the random aneuploidies are not limited to cultured cells, but also occur in vivo.

Efficiency of MicroSort flow cytometry for producing sperm populations enriched in X- or Y-chromosome haplotypes: a blind trial assessed by double and triple colour fluorescent in-situ hybridization

Using fluorescent in-situ hybridization (FISH) we have evaluated, on a blind basis, the efficiency of flow cytometry to separate human X- and Y-chromosome bearing spermatozoa. Our data demonstrate that human spermatozoa can be sorted to a purity of 80-90% for X spermatozoa and of 60-70% for Y spermatozoa. Our results using triple FISH fully agree with the sorting treatment used in each case and corroborate the efficiency of the flow sorting technique for sperm sex selection. In these limited samples (200-500 sperm/donor), the frequencies of disomic or diploid spermatozoa were not increased when comparing the sorted samples with unselected samples or with our control series.

Sephadex filtration and human serum albumin gradients do not select spermatozoa by sex chromosome: a fluorescent in-situ hybridization study

Fluorescent in-situ hybridization (FISH) of decondensed sperm nuclei has been used directly to evaluate the enrichment efficiency of human sperm separation using Sephadex gel filtration and human serum albumin (HSA) gradients. Control and processed spermatozoa were fixed and their nuclei decondensed. In-situ hybridization was carried out with a Y-specific DNA probe (DYZ1). Sephadex filtration yielded 52.5% Y-chromosome-bearing spermatozoa, HSA separation resulted in 49.4% Y-chromosome-bearing spermatozoa and in the untreated control sample the percentage of Y spermatozoa was 49.3%. Statistical analysis revealed no significant differences between the selection methods employed and the controls, and no real enrichment for X- or Y-bearing spermatozoa was detected for any of the selection methods assayed. The usefulness of the protocols reported for selection of spermatozoa by sex chromosome in couples at risk for X-linked diseases is discussed.

The genetic risks of in vitro fertilization techniques: the use of an animal model

PURPOSE

The influence of some technical and biological parameters on the genetic characteristics of embryos derived from in vitro fertilization (IVF) techniques was studied.

METHOD

Using a murine model, we assessed the effect of gamete manipulation, gamete maturation stage, and maternal age on the chromosome complements of first-cleavage embryos.

RESULTS AND CONCLUSIONS

We found a positive correlation between some of these parameters and the incidence of the different chromosome abnormalities studied. Regarding aneuploidy, we observed an influence of maternal age, using both prepubertal and old females. Polyspermy showed a positive correlation with in vitro fertilization, the immaturity and overmaturity of the oocytes employed, and the use of prepubertal females. The appearance of diploid female complements was related to oocyte immaturity and prepubertal females, while diploid male complements were directly related to in vitro fertilization. Premature chromosome condensation (PCC) had a direct relationship with oocyte immaturity and in vitro maturation of the oocyte. Finally, structural abnormalities were associated with the process of sperm aging in vitro.

Chromosomes of mouse embryos in vivo and in vitro: effect of manipulation, maternal age and gamete ageing

The use of human material does not allow the determination of the influence of different parameters on the genetic characteristics of the embryos derived from in-vitro fertilization (IVF) techniques. Using a murine model we assessed the effect of gamete manipulation, maternal age and oocyte ageing on the chromosome complements of the embryos. We have found a positive correlation between all these parameters and the incidence of chromosome abnormalities in first-cleavage mouse embryos obtained by IVF.