Gurbax S. Sekhon

Ventricular noncompaction and distal chromosome 5q deletion.

We describe a 7 1/2-year-old girl with mildly unusual phenotype and complex heart disease including ventricular myocardial noncompaction. She was found to have a distal 5q deletion, del(5)(q35.1q35.3). Fluorescent in situ hybridization showed that this deletion included the locus for the cardiac specific homeobox gene, CSX. This suggests that some instances of ventricular myocardial noncompaction may be caused by haploinsufficiency of CSX.

Utility of subtelomeric fluorescent DNA probes for detection of chromosome anomalies in 425 patients

Purpose: A complete set of subtelomeric fluorescent DNA probes, except the acrocentric p-arms, was developed in 1996, was optimized in 1998, and is commercially available. These and other fluorescence in situ hybridization (FISH) probes have been used to detect anomalies of the subtelomere regions among groups of patients with idiopathic mental retardation (MR), developmental delay (DD), and/or nonspecific dysmorphic features (NDF), and individuals with multiple miscarriages (MM) who were karyotypically normal by standard G-banding techniques.Methods: A total of 425 patients were analyzed, of whom 372 had idiopathic MR/DD/NDF and 53 were involved in MM. An effort was made to select individuals for this study who were either normal karyotypically or who had subtle chromosomal anomalies that were inconclusive by banded chromosome analysis, although this was not always possible.Results: Anomalies involving the subtelomere regions were detected at a frequency of 6.8% in the MR/DD/NDF group. The cryptic or subtle anomalies are estimated to be about 3.4%. It was necessary to use M-FISH, chromosome, and locus specific FISH probes to clarify some of the abnormalities. No abnormalities were detected in the MM group. Deletion variants were present for 2qter, 7pter, and Xpter/Ypter subtelomeric regions ranging from <1 to 9.6%.Conclusions: The subtelomeric FISH probes are instrumental in the detection of subtelomeric anomalies in a significant proportion, although no more than 50% are subtle, of patients with idiopathic MR/DD/NDF. In some cases, however, it was necessary to use other FISH probes to clarify the nature of these abnormalities. No subtelomeric abnormalities were detected in our group of 53 MM patients, suggesting a relatively low frequency of occurrence in this patient population.

Del(10)(q22.3q24,1) associated with juvenile polyposis

Juvenile polyps are the most frequent gastrointestinal polyps with a malignant potential for which the genetic basis is unknown. Juvenile polyps, with a normal epithelium but hypertrophic lamina propria, are histologically quite distinct from adenomatous polyps which have dysplastic changes in epithelial nuclei. Furthermore, the adenomatous polyposis coli (APC) gene on Chr 5, mutated somatically in adenomatous polyps and mutated in the germline of patients with familial adenomatous polyposis, is not linked to hereditary juvenile polyposis. We provide the first report indicating that a tumor suppressor gene associated with juvenile polyposis may be located at 10q22.3q24.1. Cytogenetic studies of a patient with juvenile polyposis and multiple congenital abnormalities of the head, extremities, and abdomen revealed a de novo interstitial deletion of Chr 10 as the only defect, del(10)(10q22.3q24.1).

Absence of predictable phenotypic expression in proximal 15q duplications

We describe ten individuals with an insertional duplication 15q12→q13. Phenotypic analysis of these individuals and 15 previously reported cases of proximal 15q duplications fails to show any consistent clinical manifestations. It appears that a duplication of this region is phenotypically silent.

Waisman syndrome, a human X-linked recessive basal ganglia disorder with mental retardation: Localization to Xq27.3-qter

Linkage of the gene responsible for an X-linked early onset parkinsonism disorder with mental retardation (McKusick 311510) to DNA probes that detect restriction fragment length polymorphisms is described. The disease gene is linked to the F8C gene, and to DNA probes detecting polymorphic loci DXS52, DXS15, DXS134, and DXS374 with maximum lod scores at theta = 0 of 5.08, 5.19, 5.00, 5.03, and 4.46, respectively. Multipoint linkage analysis gives a maximum multipoint lod score of 6.75 at the F8C gene. This places the disease gene in chromosomal region Xq27.3-qter.

Mapping of prolactin and tumor necrosis factor-beta genes on human chromosome 6p using lymphoblastoid cell deletion mutants.

A collection of human B lymphoblastoid cell lines (LCLs) was used to map two genetic sequences for which polymorphism had not been identified: human prolactin (PRL) and tumor necrosis factor-beta (TNFB). The LCLs have overlapping deletions on chromosome 6p produced by gamma-irradiation of LCL 721. After using two chromosome 6p sequences for which LCL 721 is heterozygous to validate our scanning denistometry (SD) method for inferring gene copy number, SD was used to map TNFBand PRL. TNFBmaps to the interval between the C4complement and HLA-Bloci within the MHC on chromosome 6p. PRLlies within the 6p21.3–6p22.2 interval distal to HLA-C.We found that LCL 721 is heterozygous for PRL DNA fragment lengths generated by HpaII but not MspI digestion, indicating that the two copies of PRLin LCL 721 are differentially methylated. This novel methylation RFLP was used to corroborate the region PRL assignment.

An XX male: Cytogenetic and endocrine studies

A 3 year old black male with ambiguous genitalia had a 46, XY karyotype in a bone marrow culture and an intermediate buccal smear result, suggestive of a mosaic of chromatin positive and chromatin negative cells. Upon re‐evaluation at age 15 years, he had a 30% positive buccal smear and a 46, XX karyotype in cultures of peripheral blood lymphocytes, skin fibroblasts, bone marrow, and testis. No Y‐body fluorescence was detectable in interphase cells from the testicular biopsy or the various cultures.

Application of multicolor fluorescent in situ hybridization for enhanced characterization of chromosomal abnormalities in congenital disorders.

OBJECTIVE To determine the efficacy of multicolor fluorescent in situ hybridization (M-FISH), which paints each chromosome in a unique color, for identification of congenital derivative and marker chromosomes. MATERIAL, METHODS AND CASES: Commercially available M-FISH probes were used to label each chromosome in a specific fluorescent color. Six representative cases involving derivative chromosomes, markers, and subtle anomalies were analyzed by M-FISH. RESULTS Three familial, rather subtle derivative chromosomes were identified by M-FISH with relative ease. A small ring that was unidentifiable by banded-chromosome analysis was identified by M-FISH. A case of a subtle telomeric anomaly could not be resolved without the use of telomeric-specific probes. The M-FISH results were confirmed by individual chromosome-specific painting probes. CONCLUSION M-FISH was helpful for identifying a wide range of congenital chromosomal anomalies. However, for subtle chromosomal abnormalities, use of locus-specific probes may be necessary.

Detection of Mosaicism in amniotic fluid cultures: A CYT02000 collaborative study

Purpose: To evaluate the assumptions on which the American College of Medical Genetics (ACMG) Standards and Guidelines for detecting mosaicism in amniotic fluid cultures are based.Methods: Data from 653 cases of amniotic fluid mosaicism were collected from 26 laboratories. A chi-square goodness-of-fit test was used to compare the observed number of mosaic cases with the expected number based on binomial distribution theory.Results: Comparison of observed data from the in situ colony cases with the expected distribution of cases detected based on the binomial distribution did not reveal a significant difference (P = 0.525).Conclusions: The empirical data fit the binomial distribution. Therefore, binomial theory can be used as an initial discussion point for determining whether ACMG Standards and Guidelines are adequate for detecting mosaicism.

Gene complementing xeroderma pigmentosum group A cells maps to distal human chromosome 9q.

Phenotypic complementation of xeroderma pigmentosum group A (XP-A) cells by microcell-mediated transfer of a single rearrangedneo-tagged human chromosome from a human-mouse somatic cell hybrid designated K3SUB1A9-3 was reported previously. Extended growth of this human-mouse hybrid in culture led to deletion of the small arm of the human chromosome, with concomitant loss of complementing ability when introduced into XP-A cells by microcell-mediated chromosome transfer. Cytogenetic analysis of both hybrids suggests that the complementing locus is on chromosome 9q22.2-q34.3, and Southern blot analysis confirms the presence of distal chromosome 9q sequences.