Catherine Sarri

Tetrasomy 18p de novo: Parental Origin and Different Mechanisms of Formation

We have used eight PCR-based DNA polymorphisms to determine the parental origin and mechanisms of formation in 9 patients with de novo nonmosaic tetrasomy 18p. The 9 patients, 4 girls and 5 boys, had clinical features characteristic of i(18p) syndrome. The supernumerary marker chromosome was identified by fluorescence in situ hybridization (FISH) analysis using centromeric probes and a flow-sorted 18p-specific library. The isochromosome was of maternal origin in all 9 cases. The formation of tetrasomy 18p cannot be explained by a single model. In 6 cases, meiosis II nondisjunction, followed by subsequent postzygotic misdivsion, and in 1 case postzygotic nondisjunction and postzygotic misdivision were the most likely mechanisms of formation. Alternative mechanisms are suggested in the remaining 2 cases.

Partial trisomy 17q22‐qter and partial monosomy Xq27‐qter in a girl with a de novo unbalanced translocation due to a postzygotic error: Case report and review of the literature on partial trisomy 17qter

Partial trisomy 17q22-qter is a rare but well-recognized clinical entity. We present a case of partial trisomy for the long arm of chromosome 17, which was detected in a female infant with severe psychomotor and somatic retardation, Stargardt disease, short limbs, and numerous minor anomalies. Differential chromosomal staining demonstrated an excess of genetic material on the long arm of the late replicating X chromosome. FISH and DNA polymorphism analysis showed that the extra material belonged to the distal part of the long arm of chromosome 17 and that there was a partial monosomy of the distal part of the long arm of the derivative X chromosome. The breakpoint regions of this translocation were identified by molecular analysis using polymorphic microsatellite markers on human chromosomes 17 and X. The origin of the abnormal X chromosome was found to be paternal, whereas the origin of the duplicated part of chromosome 17 was maternal. The unbalanced translocation between the paternal X and the maternal chromosome 17 is, therefore, suggested to be due to a postzygotic error.

A report of pure 7p duplication syndrome and review of the literature

We report on a case of a 9‐month‐old female infant with a direct duplication of the 7p13‐p22.1 chromosome region diagnosed by combining conventional cytogenetic, FISH, and multicolor banding (MCB) studies. Traditional G‐banding detected a partial 7p duplication, which was further demonstrated to be entirely of chromosome 7 origin by using a whole chromosome paint for chromosome 7, and derived from 7p13‐p22.1 by MCB. The infant presented with characteristic dysmorphic features, psychomotor retardation, and generalized hypotonia. The phenotypic manifestations of partial 7p trisomy with or without other chromosome involvement are briefly reviewed. Our observations in combination with other cases confirm that 7p trisomy due to dir dup(7p) can be regarded as a defined chromosome syndrome.

Double supernumerary isodicentric chromosomes derived from 15 resulting in partial hexasomy

We report two unrelated patients each with two supernumerary marker chromosomes (SMCs) derived from chromosome 15, and thus resulting in partial hexasomy. Hexasomy in the one case (family 1) was diagnosed at prenatal diagnosis and did not include the Prader–Willi/Angelman critical region (PWACR). The double SMCs were also found in the mother, the pregnancy continued to term, and an apparently phenotypically normal child was born. This represents the first report of transmission of double SMCs from mother to child. In the second case (family 2), the hexasomy did include the PWACR and was de novo in origin. This patient manifested severe psychomotor retardation, clefting of the soft palate, hypotonia, seizure‐like episodes, and other phenotypic features. The aberrant phenotype is attributable to the hexasomy for the PWACR gene loci. The normal homologs of chromosome 15 proved to be biparental in origin while the two SMCs appeared maternal.

Pure de novo partial trisomy 6p in a girl with craniosynostosis.

Duplications of chromosome 6p are rarely reported. We present the case of a girl with a de novo trisomy 6p12.3–p21.1 who showed clinical features characteristic of this syndrome, notably facial anomalies, psychomotor delay, and recurrent respiratory tract infections. The most striking feature, however, was craniosynostosis, manifested by the premature fusion of the right coronal and sagittal sutures. A review of the literature revealed that the presence of abnormal fontanelles and sutures is relatively common among patients with proximal trisomy 6p. Exclusion of the most frequently occurring craniosynostosis mutations, as well as of further chromosomal anomalies in our case, suggest the presence of a gene regulating suture formation within this region. Based on recent findings, we hypothesize that the runt‐related transcription factor 2 (RUNX2) may be a reasonable candidate gene for craniosynostosis in such patients.

Combined 22q11.1-q11.21 deletion with 15q11.2-q13.3 duplication identified by array-CGH in a 6 years old boy

BackgroundDeletions of chromosome 22q11 are present in over 90% of cases of DiGeorge or Velo-Cardio-Facial syndrome (DGS/VCFS). 15q11-q13 duplication is another recognized syndrome due to rearrangements of several genes, belonging to the category of imprinted genes. The phenotype of this syndrome varies but has been clearly associated with developmental delay and autistic spectrum disorders. Co-existence of the two syndromes has not been reported so far.ResultsHere we report a 6-year-old boy presenting growth retardation, dysmorphic features and who exhibited learning difficulties. Fluorescence in situ hybridization (FISH) analysis of the proband revealed a deletion of DiGeorge Syndrome critical region (TUPLE). Array-CGH analysis revealed an interstitial duplication of 12 Mb in size in the area 15q11.2-q13.3, combined with a 3.2 Mb deletion at region 22q11.1-q11.21. FISH analysis in the mother showed a cryptic balanced translocation between chromosome 15 and chromosome 22 (not evident by classic karyotyping).DiscusionThe clinical manifestations could be related to both syndromes and the importance of array-CGH analysis in cases of unexplained developmental delay is emphasized. The present case further demonstrates how molecular cytogenetic techniques applied in the parents were necessary for the genetic counseling of the family.

Sister-chromatid exchange in highly purified human CD4+ and CD8+ lymphocytes

Sister-chromatid exchange (SCE) frequencies were determined in human peripheral blood CD4+ and CD8+ T lymphocyte subpopulations which were rapidly and highly purified from pooled T lymphocytes by immunological methods. The purified lymphocytes were stimulated with phytohemagglutinin (PHA) for 4 days. CD4+ lymphocytes showed significantly higher SCE frequencies than autologous CD8+ lymphocytes when measured simultaneously after identical bromodeoxyuridine (BrdU) incubation times. Differences in SCE frequencies between CD4+ and CD8+ lymphocytes were also detected when mitomycin C (MMC) was added to the cultures. Higher SCE frequencies in CD4+ lymphocytes were associated with lower proliferating rate indices (PRI) as compared to autologous CD8+ lymphocytes. Abnormalities in CD4+ T lymphocyte function and number in peripheral blood have been observed in several diseases characterized by immunological disorders. Thus, our data may suggest a link between some immunological disturbances and abnormal SCE frequencies in T lymphocyte subsets.

Supernumerary marker chromosome 5 diagnosed by M-FISH in a child with congenital heart defect and unusual face.

We describe a female patient with a small supernumerary marker chromosome (sSMC) present in mosaic and characterized in detail by fluorescence in situ hybridization (FISH) using all 24 human whole chromosome painting probes, multicolor banding (MCB) and subcentromere specific multicolor FISH (subcenM-FISH). The sSMC was demonstrated to be derived from chromosome 5 and the karyotype of our patient was as follows: 47,XX,+mar.ish r(5)(::p13.2∼p13.3→q11.2::) [60%]/46,XX [40%]. Partial trisomy for the proximal 5p and q chromosomal regions is a rare event. A critical region exists at 5p13 for the phenotype associated with duplication 5p. As far as we know, eight similar cases have been published up to now. We describe a new case which, to our knowledge, is the first characterized in such detail. The role of uniparental disomy (UPD) in cases of SMC is also discussed.

Complex distal 10q rearrangement in a girl with mild intellectual disability: Follow up of the patient and review of the literature of non-acrocentric satellited chromosomes†

We report on an intellectually disabled girl with a de novo satellited chromosome 10 (10qs) and performed a review of the literature of the non‐acrocentric satellited chromosomes (NASC). Satellites and stalks normally occur on the short arms of acrocentric chromosomes; however, the literature cites several reports of satellited non‐acrocentric chromosomes, which presumably result from a translocation with an acrocentric chromosome. This is, to our knowledge, the third report of a 10qs chromosome. The phenotype observed in the proband prompted a search for a structural rearrangement of chromosome 10q. By microsatellite analysis we observed a 4 Mb deletion on the long arm of chromosome 10, approximately 145 kb from the telomere. FISH and array CGH analyses revealed a complex rearrangement involving in range from the centromere to the telomere: A 9.64 Mb 10q26.11–q26.2 duplication, a 1.3 Mb region with no copy number change, followed by a 5.62 Mb 10q26.2–q26.3 deletion and a translocation of satellite material. The homology between the repeat sequences at 10q subtelomere region and the sequences on the acrocentric short arms may explain the origin of the rearrangement and it is likely that the submicroscopic microdeletion and microduplication are responsible for the abnormal phenotype in our patient. The patient presented here, with a 15‐year follow‐up, manifests a distinct phenotype different from the 10q26 pure distal monosomy and trisomy syndromes.

De novo inverted interstitial duplication 8q22.1‐q21.1 in a boy with moderate learning disabilities, mild autistic and dysmorphic features

We describe a 13 1/2‐year‐old boy with de novo inverted interstitial duplication 8q22.1‐q21.1 associated with mild phenotypic abnormalities, learning disabilities and autism. Psychometric and psychiatric evaluation was performed. Clinical genetic evaluation was supported by chromosome analysis of blood lymphocytes using GTG‐banding technique and Fluorescent In Situ Hybridization (FISH) with whole chromosome painting 8 probe. Clinical evaluation revealed mild phenotypic abnormalities, moderate learning disabilities and mild autistic disorder. The karyotype of the proband was interpreted as 46, XYqh+pat, 8q+.ish inv dup(8)(q22.1;q21.2)(wcp8+) de novo. Although partial trisomy for other segments of 8q, as well as mosaic trisomy 8, have been described in numerous cases, interstitial duplication of 8q21‐q22 seems extremely rare and the severity of the phenotypic abnormalities ranges from mild to profound.