Mosaic tetrasomy 8p: molecular cytogenetic confirmation and measurement of glutathione reductase and tissue plasminogen activator levels

Prenatal diagnosis of mosaic tetrasomy 8p

Tetrasomy 8p is a rare chromosomal disorder that has only been detected in a mosaic form. At the present time, 11 cases have been reported; their phenotype included agenesis of the corpus callosum, enlarged ventricles, minor facial dysmorphism, rib and vertebral anomalies, and mild to moderate developmental delay. To the best of our knowledge, tetrasomy 8p has never been prenatally diagnosed. This 43-year-old woman was referred for amniocentesis at 20 weeks' gestation because of advanced maternal age. Amniotic fluid cells were cultured according to standard techniques by the in situ method. A supernumerary chromosomal marker was detected in a single clone of cultured amniotic cells and interpreted by RHG banding as an isochromosome of the short arm of chromosome 8 (i(8p)). The ultrasound investigation at 27 weeks gestation revealed enlarged ventricles and agenesis of the corpus callosum, which were confirmed at fetal autopsy after medical termination of the pregnancy. Chromosomal analyses, including RHG banding and FISH, of several tissues showed different levels of i(8p) mosaicism. Whereas no i(8p) was detected on cytotrophoblast nor additional amniotic fluid cells, 97% and 30% of cells from long-term cultures of placenta and lymphocytes, respectively, had the i(8p). Using DNA markers, the isochromosome 8p was interpreted as the result of a prezygotic event during maternal meiosis. Our findings suggest that the i(8p) is the subject of tissue selection. Tetrasomy 8p might be underdiagnosed during pregnancy; therefore, karyotyping on a fetal blood sample following detection of agenesis of the corpus callosum when no chromosomal abnormality has been found on the amniotic fluid cell cultures should be discussed with the parents.

Familial dup(8)(p12p21.1): mild phenotypic effect and review of partial 8p duplications

We describe a family with direct transmission of a duplication of 8p12-->8p21.1. The phenotype of affected relatives included mild mental retardation but no minor anomalies. The duplication was identified by means of GTG-banding and fluorescence in situ hybridization with a probe specific for 8p12 generated by microdissection and degenerate oligonucleotide primed-polymerase chain reaction. Assay of glutathione reductase, which has been localised to 8p21.1, was significantly increased when compared with controls with normal chromosomal constitution. To the best of our knowledge, a proximal direct duplication of 8p restricted to subbands p12-->p21.1 has not been reported so far. The reported aberration is compared with other partial duplications of 8p, in particular to inversion duplications 8p and to small direct distal duplications involving 8p23.1. Am. J. Med. Genet. 94:306-310, 2000.

Complex congenital heart malformations in mosaic tetrasomy 8p: case report and review of the literature

We describe a 5-month-old boy with complex congenital heart defects (dTGA, DORV, VSD, ASD, and PDA), minor facial and ear anomalies, deep palmar creases, multiple vertebral anomalies, agenesis of the corpus callosum, and mosaic tetrasomy 8p (47,XY,+i(8)(p10)[88%]/46,XY[12%] in blood with normal chromosomes in cultured skin fibroblasts. This infant represents the eleventh reported case of mosaic tetrasomy 8p since its first description by Kristofferson et al. [1988: Clin Genet 34:201-203]. The pattern of heart malformations and discordance of blood and fibroblast karyotypes make our case unique. Our report and review suggest that an important distinction between mosaic tetrasomy 8p and other chromosome 8 aneuploidies involves the increased incidence and complexity of congenital heart malformations.

Unravelling the genetics of vesicoureteric reflux: a common familial disorder

Primary vesicoureteric reflux (VUR) is one of the more common genetic disorders. Little is yet known about the genetics of this potentially manageable childhood condition, which is characterised by regurgitation of urine from the bladder to the kidney. The VUR phenotype is associated with shortness of the submucosal segment of the ureter due to congenital lateral ectopia of the ureteric orifice. VUR is found in 30-50% of infants and young children with a urinary tract infection. A serious concern in families with an affected patient is that approximately one half of siblings or offspring will be affected, but up to a half of these affected siblings and offspring may be asymptomatic in childhood. If left untreated, these patients may present later in life with proteinuria, hypertension or renal failure. VUR is the commonest cause of end-stage renal failure in children, and an important cause in adults. As the kidney damage resulting from severe VUR is preventable, early detection is desirable. The techniques for clinical diagnosis are invasive and costly, reinforcing the importance of identification of a gene for VUR to facilitate genetic screening. Although family studies suggest a major dominant gene, the inheritance pattern is still a matter of debate. In rare instances, VUR occurs in association with other diseases, such as the coloboma-ureteric-renal syndrome, which is caused by a PAX2 gene mutation. In this review, we present evidence that this common disorder may be caused by mutations in the developmental pathway of which the PAX2 gene forms a part.

Mosaic "tetrasomy" 8p: case report and review of the literature

A male infant presenting with multiple anomalies including a midline cleft palate, anasarca, hepatomegaly, pulmonary edema, agenesis of the corpus collosum, and complex congential cardiac anomalies was found to have mosaicism for an additional chromosome that appeared (following GTG-banding and FISH) to be a monocentric isochromosome of the short arm of chromosome 8 (46,XY/47,XY, +i(8p)). Nine other cases of mosaicism for an additional i(8p) were reviewed. Considerable phenotypic variation was noted. Consistent features were identified including agenesis of the corpus callosum, cardiac malformations, and minor facial dysmorphology. The phenotype of these patients partially overlaps those of trisomy 8 and trisomy 8p. By studying additional individuals with this condition, mosaic tetrasomy 8p may emerge as a recognizable clinical phenotype.

Trisomy 7p resulting from isochromosome formation and whole-arm translocation

A newborn boy with a large anterior fontanel, minor facial anomalies, postaxial polydactyly, patent ductus arteriosus, and developmental delay had trisomy of 7p due to an i(7p) and a concomitant t(2;7) (q37.3;q11.1). Significant enlargement of the fontanel is the most characteristic finding in most patients with duplications involving 7p15-pter. Asynchrony in fore- and hindbrain and hemisphere formation leading to brain asymmetry and various defects in the posterior fossa are typical of infants with duplications of 7p11-p12. A variety of heart defects has also been found in more than 50% of patients with duplication of 7p segments. Isochromosome formation accompanied by whole-arm translocation, resulting in uniparental isodisomy for the involved segment, is an extremely rare cause leading to partial trisomies. Although it is not clear whether isochromosome formation precedes the whole-arm translocation or follows it, the secondary rearrangement may have adaptive significance.

Mosaic tetrasomy 8p in two patients: clinical data and review of the literature

We report on 2 girls with mosaic tetrasomy 8p. Patient 1 showed the extra iso 8p chromosome in 20% of cultured lymphocytes and 18% of cultured fibroblasts [46,XX/47,XX,+i(8p)]. She presented with growth retardation, mild facial alterations, and motor developmental delay. Patient 2 presented with developmental delay, hypotonia, and slight facial alterations; she had the extra iso 8p chromosome in 94% of cultured peripheral lymphocytes. The patients are compared to the 6 previously reported cases. In our experience, the presently reported patients clinically resemble children with inv dup(8)(p21-p22) and patients with mosaic trisomy 8.