Ring chromosome 12 with variable phenotypic features: clinical report and review of the literature

Chromosomal abnormalities and Y chromosome microdeletions in infertile men with azoospermia and oligozoospermia in Eastern China

Objective

The objective was to investigate the frequency and type of chromosomal abnormalities and Y chromosome microdeletions in infertile men with azoospermia and oligozoospermia to ensure appropriate genetic counseling before assisted reproduction in Eastern China.

Methods

A total of 201 infertile men (148 with azoospermia and 53 with oligozoospermia) were enrolled. Real-time PCR using six Y-specific sequence-tagged sites of the azoospermia factor (AZF) region was performed to screen for microdeletions. Karyotype analyses were performed on peripheral blood lymphocytes with standard G-banding.

Results

Out of 201 infertile patients, 22 (10.95%) had Y microdeletions [17/148 (11.49%) men with azoospermia and 5/53 (9.43%) men with oligozoospermia]. The most frequent microdeletions were in the AZFc region, followed by the AZFa+b + c, AZFb+c, AZFa, and AZFb regions. Chromosomal abnormalities were detected in 18.91% (38/201) of patients, 34 of which were sex chromosome abnormalities (16.92%) and 4 of which were autosomal abnormalities (1.99%). Chromosomal abnormalities were more prevalent in men with azoospermia (22.97%) than in those with oligozoospermia (7.55%).

Conclusions

We detected a high incidence of chromosomal abnormalities and Y chromosomal microdeletions in infertile Chinese men with azoospermia and oligozoospermia. These findings suggest the need for genetic testing before the use of assisted reproduction techniques.

Ring chromosome 12 with inverted microduplication of 12p13.3 involving the Von Willebrand Factor gene associated with cryptogenic stroke in a young adult male

We report a 35-year-old male with a ring chromosome 12 originally diagnosed 20 years prior to presentation with an ischemic stroke. Array CGH analysis revealed a sub-microscopic microdeletion and microduplication within 12p13.3 and a microdeletion in 12q24.33. FISH analysis further revealed that the duplication was in an inverted orientation and included exons 35-52 of the dosage-sensitive Von Willebrand Factor (VWF) gene. Partial duplication of this gene, which has a role in the clotting cascade, suggests a potential mechanism for generating a pro-thrombotic state that may have contributed to a premature cerebrovascular event. Evidence of raised VWF antigen levels and VWF activity levels in the highest quartile provides support for this hypothesis. This case illustrates that when a ring chromosome is identified, the possibility of cryptic genomic rearrangements needs to be considered as these may have implications in predicting natural history.

Ring chromosome 12 and severe oligospermia: a case report

OBJECTIVE

To describe an unusual presentation of ring chromosome 12, which manifested as severe azoospermia, resulting in male infertility.

DESIGN

Case report.

SETTING

In vitro fertilization center at a tertiary care hospital.

PATIENT(S)

A 27-year-old man diagnosed with unexplained azoospermia and ring chromosome 12 abnormality during a workup for primary infertility.

INTERVENTION(S)

In vitro fertilization with preimplantation genetic diagnosis.

MAIN OUTCOME MEASURE(S)

To confirm the importance of obtaining karyotypes in individuals with severe oligospermia.

RESULT(S)

Full-term pregnancy after IVF using donor sperm.

CONCLUSION(S)

Severe oligospermia and male infertility should be included in the spectrum of findings found in ring chromosome 12.

Mosaic ring 20 with no detectable deletion by FISH analysis: Characteristic seizure disorder and literature review

Ring chromosome 20 is a rare chromosome disorder characterized by a typical seizure phenotype consisting of complex partial seizures, frequent progression to generalized tonic or tonic-clonic seizures, and nocturnal frontal lobe seizures with frequent episodes of non-convulsive status epilepticus. Development may be normal or mildly delayed, followed by cognitive and behavioral decline after seizure onset. Here, we describe a patient with a typical severe seizure phenotype and a mosaic ring chromosome 20 without loss of p or q subtelomere regions or telomeric sequences. The ring had a longer telomere length than either of the telomere ends of its homologous chromosome 20 by quantitative fluorescence in situ hybridization analysis, suggesting that it might be derived from telomere-telomere fusion. The phenotypic comparison of this patient and other chromosome 20 cases that had terminal deletions of 20qter (n = 1) and 20pter (n = 7), shows that the epilepsy phenotype and electroencephalographic abnormalities are characteristic in patients with ring chromosome 20. Several hypotheses have been proposed to address the elusive mechanisms underlying the seizure disorder in ring chromosome 20. These possibilities include haploinsufficiency of two epilepsy genes CHRNA4 and KCNQ2 located at 20qter, silencing of these genes by a telomere position effect, or microdeletions or rearrangements of genetic material during the ring formation.

Detailed clinical description of four patients with 1.3 and 2.1 Mb chromosome imbalances derived from a familial t(12;17)(q24.33;q25.3)

We describe a family carrying a submicroscopic reciprocal translocation involving 12qter and 17qter detected by subtelomeric FISH analysis. Four family members inherited unbalanced variants-two cases inherited the derivative chromosome 12 and the other two the derivative chromosome 17. The two individuals with the derivative chromosome 17 showed a distinct phenotype with mild mental retardation in combination with multiple minor malformations, while the phenotype in the cases with the derivative chromosome 12 was milder and only partly concordant. Detailed FISH analysis using 19 BAC clones covering the distal part of chromosome 12q and 17q estimated the imbalances to 2.1 and 1.3 Mb, respectively. The clinical and cytogenetic findings of the two different genotypes are reported and discussed. This family illustrates that small chromosome imbalances can be detected in individuals with mild phenotype and normal, or near-normal, cognitive functions.