First report of a partial trisomy 3q12-q23 de novo--FISH breakpoint determination and phenotypic characterization

Retrospective karyotype study in mentally retarded patients

OBJECTIVE

To describe the chromosomal alterations in patients with mental retardation (MR) using G-banding karyotype analysis.

METHOD

A retrospective study of the results G-banding karyotype analysis of 369 patients investigated for MR was performed. Based on the structural rearrangements found, the authors searched all chromosomal regions related with breakpoints, and these were compared with the literature on MR and databases.

RESULTS

338 (91.6%) normal cases, and 31 (8.4%) with some type of chromosomal abnormality were identified. Among the altered cases, 21 patients (67.8%) were identified with structural chromosomal alterations, nine (29%) with numerical alterations, and one (3.2%) with numerical and structural alterations.

CONCLUSION

Structural chromosomal abnormalities were observed more frequently in this study. G-banding karyotyping contributes to the investigation of the causes of MR, showing that this technique can be useful for initial screening of patients. However, higher resolution techniques such as array based comparative genomic hybridization (aCGH) and multiplex ligation-dependent probe amplification (MPLA) can detect submicroscopic alterations commonly associated with MR.

Prenatally diagnosed partial trisomy 3q case with an omphalocele and less severe phenotype

Trisomy 3q is a very rarely reported chromosomal disorder. Duplication of part of the long arm of human chromosome 3 causes a distinct and severe syndrome that leads to multiple congenital abnormalities. A 27 year-old pregnant woman was admitted to our clinic at 17 weeks of gestation. Prenatal sonography identified a fetus with an omphalocele that contained the liver and bowel, mild ventriculomegaly and polyhydramnios. Amniocentesis revealed the karyotype of 46, XY, der (3) (3qter→3q21: : 3pter→3qter). The pregnancy was subsequently terminated. Postnatally, the proband showed midfacial hypoplasia, micrognathia, hypoplastic 12th ribs, omphalocele and prominent heels. We reported this partial trisomy 3q case because he had less marked malformations compared to other reported cases and also different features such as an omphalocele and hypoplastic 12th rib which have not been described previously in an isolated Trisomy 3q case with this karyotype.

Clinical characterization of individuals with deletions of genes in holoprosencephaly pathways by aCGH refines the phenotypic spectrum of HPE

Holoprosencephaly (HPE) is the most common developmental forebrain anomaly in humans. Both environmental and genetic factors have been identified to play a role in the HPE phenotype. Previous studies of the genetic bases of HPE have taken a phenotype-first approach by examining groups of patients with HPE for specific mutations or deletions in known or candidate HPE genes. In this study, we characterized the presence or absence of HPE or a microform in 136 individuals in which microarray-based comparative genomic hybridization (aCGH) identified a deletion of one of 35 HPE loci. Frank holoprosencephaly was present in 11 individuals with deletions of one of the common HPE genes SHH, ZIC2, SIX3, and TGIF1, in one individual with a deletion of the HPE8 locus at 14q13, and in one individual with a deletion of FGF8, whereas deletions of other HPE loci and candidate genes (FOXA2 and LRP2) expressed microforms of HPE. Although individuals with deletions of other HPE candidates (DISP1, LSS, HHIP, SMO, BMP4, CDON, CDC42, ACVR2A, OTX2, and WIF1) had clinically significant features, none had frank HPE or a microform. A search for significant aCGH findings in individuals referred for testing for HPE revealed a novel association of a duplication involving GSK3B at 3q13.33 with HPE or a microform, seen in two unrelated individuals.