Inverted duplication with deletion: first interstitial case suggesting a novel undescribed mechanism of formation

Inverted duplications with terminal deletions are a well-defined family of complex rearrangements already observed for most of chromosome extremities. Several mechanisms have been suggested which could lead to their occurrence, either through non-homologous end joining, non-allelic homologous recombination, or more recently through an intrastrand fold-back mechanism. We describe here a patient with intellectual disability and pharmacoresistant epilepsy, for which array CGH analysis showed the first interstitial case of inverted duplication with deletion on chromosome 1p. Furthermore, SNP array analysis revealed an associated segmental isodisomy for the distal part of 1p, which led us to consider a replicative mechanism to explain this abnormality. This observation extends the range of this once telomeric rearrangement.

Translocation (Y;22) resulting in the loss of SHOX and isolated short stature

Chromosomal rearrangements involving both chromosome Y and chromosome 22 are rare, and may result in a number of different phenotypes. We report on a 4-year-old child with short stature and a dicentric chromosome with a deletion of the distal end of chromosome Yp. The pregnancy was uneventful, until intra-uterine growth retardation was noted. Prenatal karyotyping showed a (Y;22) translocation. No structural fetal abnormality was shown at ultrasound examination, and the pregnancy went to term. A growth-retarded boy with an otherwise normal physical examination was delivered at 39 weeks. At age 4, the child had short stature (-3 SD) without mental retardation. Radiological examination of the wrist was normal. A blood karyotype confirmed the chromosomal rearrangement previously seen on the amniotic fluid cells. C-banding showed a dicentric chromosome, and fluorescence in situ hybridization (FISH) with centromeric probes confirmed the presence of both chromosome Y and 22 centromeres on the derivative chromosome. The karyotype was thus 45,X,der(Y;22)(p11;q11)del(Y)(p11p11). Our patient's phenotype and chromosomal rearrangement prompted us to further investigate the distal Yp region. FISH using a subtelomeric probe showed a deletion of the distal Yp region. This technique also revealed that this chromosomal rearrangement resulted in the deletion of SHOX but not SRY. Although haploinsufficiency of SHOX may result in Léri-Weill Dyschondrosteosis, this diagnosis did not seem obvious in this young patient. This observation confirms the importance of FISH in the investigation of chromosomal abnormalities, and further delineates the phenotype of SHOX deleted patients.

Pregnancy outcome following prenatal diagnosis of an isodicentric X chromosome: first case report

An isodicentric X chromosome, idic (X)(q27) was found in a female fetus during cytogenetic studies performed on amniotic cells due to advanced maternal age. No mosaicism was observed. Although segmental inversion duplications have been described for several other chromosomes, isodicentric chromosomes are reported only for gonosomes. Genetic counselling was based on ultrasound findings, cytogenetic replication studies and published cases of X chromosomes duplications ascertained pre- and postnatally. The pregnancy resulted in the birth of a healthy female infant.

Polymerase Chain reaction generated probes for fluorescence in situ hybridization

The extended use of Fish with centromeric probes in many cytogenetic laboratories is often impaired by the cost of this technique. Polymerase Chain Reaction (PCR) constitutes a simple way to generate and label such centromeric probes at low cost. Two types of human DNA source can be used: 1--Somatic hybrid cell lines containing a unique human chromosome. The specific amplification of the human subset of alphoid DNA is realised with a primer pair specific for the consensus region of human alpha satellite sequence. 2--Total Human DNA. This time, a primer pair specific for the alpha satellite DNA of the chromosome of interest must be designed. These probes, labelled during the PCR reaction by direct incorporation of modified dUTP, are actually widely used in our laboratory, alone or mixed with other probes (chromosome painting or locus specific probes).

French multi-centric study of 2000 amniotic fluid interphase FISH analyses from high-risk pregnancies and review of the literature

This prospective and multi-centric study confirms the accuracy and the limitations of interphase FISH and shows that any cytogenetics laboratory can perform this technique. With regard to the technical approach, we think that slides must be examined by two investigators, because the scoring may be subjective. The main problem with the AneuVysion kit concerns the alpha satellite probes, and especially the chromosome 18 probe, which is sometimes very difficult to interpret because of the high variability of the size of the spots, and this may lead to false negative and uninformative cases. The best solution would be to replace these probes by locus-specific probes. Concerning clinical management, we offer interphase FISH only in very high-risk pregnancies or/and at late gestational age because of the cost of the test. We think that an aberrant FISH result can be used for a clinical decision when it is associated with a corresponding abnormal ultrasound scan. In other cases, most of the time, we prefer to wait for the standard karyotype.

Heteromorphism 18ph+ : with or without reproductive consequences?

Heteromorphism or chromosomal variants are usually attributed to structural variations in constitutive heterochromatin. In the case of chromosome 18, 25 cases of 18ph+ have been reported to date. Using the Primed In Situ Labelling technique (PRINS) to study 2 new cases of 18ph+, we have been able to confirm their molecular nature and assuming a mechanism of formation. Although such chromosomal variants are usually thought to have no adverse clinical consequence, a review of the literature shows that many cases were diagnosed because of recurrent abortion, malformed or mentally retarded children suggesting the possible relationship between 18ph+ and such clinical outcomes.

45,X/46,XY mosaicism: report of 27 cases

OBJECTIVES

There exist substantial differences between prenatally and postnatally diagnosed cases of 45,X/46,XY mosaicism. Ninety percent of prenatally diagnosed cases show a normal male phenotype, whereas the postnatally diagnosed cases show a wide spectrum of phenotypes. This 10% risk of an abnormal outcome in prenatally diagnosed cases requires further attention. The purpose of the present study is to provide more information on the postnatally diagnosed 45,X/46,XY mosaicism cases. To date, only a few series have been reported. An accurate diagnosis in these patients is essential not only to their follow-up, but also to providing appropriate genetic counselling and subsequent prenatal diagnosis to their parents.

METHODS

The clinical, cytogenetic, endocrinologic, histologic and molecular biological findings of 27 patients with 45, X/46,XY mosaicism are analyzed.

RESULTS

The reported cases showed a wide spectrum of phenotypes as Turner syndrome, mixed gonadal dysgenesis (MGD), male pseudohermaphroditism (MPH) and apparently normal male. However, Ulrich-Turner stigmata were the most common features found in this series. Patients with MGD or MPH presented with various degrees of sex reversal such as hypospadias and/or abnormal internal genitalia. No correlation between the proportion of the 45,X/46,XY cell lines in the blood or the fibroblasts and the phenotype was found. Mild mental retardation was present in 4 of the patients and 2 patients showed signs of autism.

CONCLUSIONS

Two major points are emphasized in this series: 1) the presence in 7 histologically analyzed streak gonads of a homogeneous 45,X chromosomal complement suggests that the invasion of the primitive genital ridge by a such a cell line may induce abnormal gonadal development; 2) 3 males, apparently normal at birth, developed late onset abnormalities such as dysgenetic testes leading to infertility, Ulrich-Turner stigmata, dysmorphic features, and mild mental retardation. These data indicate the importance of an accurate clinical and histologic evaluation of any patient presenting with 45, X/46,XY mosaicism.