Array-CGH characterization of a prenatally detected de novo 46,X,der(Y)t(X;Y)(p22.3;q11.2) in a male fetus

Recurrent Xp22.31-Yq11 Unbalanced Translocations: Molecular Diagnosis and Clinical Implications in Three Families

Unbalanced translocation between chromosomes X and Y is a recurring chromosomal rearrangement. The presence of a derivative chromosome X (derX), where a Yq11-qter segment is attached to the short arm of chromosome X, replacing a terminal Xpter-p22.31, poses challenges for interpretation of findings by prenatal cell-free DNA (cfDNA) screening, establishing genotype-phenotype correlation in male and female individuals, and for genetic counseling. In this report, we provide clinical outcomes, inheritance, and clinical implications of derX in three families referred to diagnostic testing due to discrepant results for sex chromosomes reported by cfDNA, abnormal prenatal ultrasound findings, recurrent pregnancy losses, or affected family members with derX transmitted through multiple generations. Reports of discrepant sex and risk for sex chromosome aneuploidy such as 45,X, 47,XXY and 47,XYY are common false positive outcomes of a prenatal cfDNA screening if either a mother or a fetus has unbalanced Xp-Yq translocation. In addition, mothers who carry der(X) facing a recurrent risk of ambiguity in prenatal testing. Pregnancy loss and neonatal death/stillbirth of male offspring are common in affected families, but this risk does not directly correlate with the size of deleted Xp region. This study emphasizes the importance of CMA and familial testing for accurate diagnosis and genetic counseling.

Unbalanced X;9 translocation in an infertile male with de novo duplication Xp22.31p22.33

PURPOSE

Male carriers of an X-autosome translocation are generally infertile, regardless of the position of the breakpoint on the X chromosome while the pathogenicity of Xp22.3 subtelomeric duplications is under debate. To shed light into this controversy, we present a rare case, of an azoospermic male with no other significant clinical findings, in whom classical cytogenetics revealed additional unbalanced chromosomal material, at the telomere of the long arm of one homolog of chromosome 9.

METHODS

In peripheral blood specimens of the index case and his parents, we performed GBanding, Inverted-DAPI Banding, AgNOR staining, Telomere specific Fluorescence in Situ Hybridization (FISH), Molecular karyotyping by Multi-color FISH, whole genome SNP microarrays, sub-telomeric MLPA, and transcription analysis of the expression of KAL1 gene by RT-PCR.

RESULTS

Multi-color FISH revealed an unbalanced translocation involving the short arm of chromosome X. SNP microarray analysis combined to classical cytogenetics and MLPA demonstrated a de novo 8.796 Mb duplication of Xp22.31-p22.33. Compared to three control specimens, the patient presented significantly elevated expression levels of KAL1 mRNA in peripheral blood, suggesting transcriptional functionality of the duplicated segment.

CONCLUSIONS

The duplicated segment contains the pseudo-autosomal region PAR1 and more than 30 genes including SHOX, ARSE, STS, KAL1, and FAM9A and is not listed as polymorphic. Our data advocate that duplications of the Xp22.3 region may not be associated with a clinical consequence.

Characterization of the first adult de novo case of 46,X,der(Y)t(X;Y)(p22.3;q11.2)

Herein, we describe a case of an infertile man detected in postnatal diagnosis with FISH characterization and array-CGH used for genome-wide screening which allowed the identification of a complex rearrangement involving sex chromosomes, apparently without severe phenotypic consequences. The deletion detected in our patient has been compared with previously reported cases leading us to propose a hypothetical diagnostic algorithm that would be useful in similar clinical situations, with imperative multi disciplinary approach integrated with genetic counseling. Our patient, uniquely of reproductive age, is one of six reported cases of duplication of Xp22.3 (~8.4Mb) segment and contemporary deletion of Yq (~42.9Mb) with final karyotype as follows: 46,X,der(Y),t(X;Y)(Ypter→Yq11.221::Xp22.33→Xpter).ish der(Y) (Yptel+,Ycen+,RP11-529I21+,RP11-506M9-Yqtel−,Xptel+). arrXp22.33p22.31(702–8,395,963, 8,408,289x1), Yq11.221q12 (14,569,317x1, 14,587,321–57,440,839x0).