A boy with developmental delay and mosaic supernumerary inv dup(5)(p15.33p15.1) leading to distal 5p tetrasomy - case report and review of the literature.

BACKGROUND: With only 11 patients reported, 5p tetrasomy belongs to rare postnatal findings. Most cases are due to small supernumerary marker chromosomes (sSMCs) or isochromosomes. The patients share common but unspecific symptoms such as developmental delay, seizures, ventriculomegaly, hypotonia, and fifth finger clinodactyly. Simple interstitial duplications leading to trisomies of parts of 5p are much more frequent and better described. Duplications encompassing 5p13.2 cause a defined syndrome with macrocephaly, distinct facial phenotype, heart defects, talipes equinovarus, feeding difficulties, respiratory distress and anomalies of the central nervous system, developmental delay and hypotonia. CASE PRESENTATION: We present a boy with dysmorphic features, developmental delay, intellectual disability and congenital anomalies, and a mosaic sSMC inv dup(5)(p15.33p15.1). He is the fourth and the oldest reported patient with distal 5p tetrasomy. His level of mosaicism was significantly different in lymphocytes (13.2%) and buccal cells (64.7%). The amplification in our patient is smaller than that in the three previously published patients but the only phenotype difference is the absence of seizures in our patient. CONCLUSIONS: Our observations indicate that for the assessment of prognosis, especially with respect to intellectual functioning, the level of mosaicism could be more important than the extent of amplification and the number of extra copies. Evaluation of the phenotypical effect of rare chromosomal aberrations is challenging and each additional case is valuable for refinement of the genotype-phenotype correlation. Moreover, our patient demonstrates that if the phenotype is severe and if the level of sSMC mosaicism is low in lymphocytes, other tissues should be tested.

Molecular Cytogenetic Diagnostics of Marker Chromosomes: Analysis in Four Prenatal Cases and Long-Term Clinical Evaluation of Carriers.

The prenatal finding of a small supernumerary marker chromosome (sSMC) is a challenge for genetic counseling. Our analytic algorithm is based on sSMC frequencies and multicolor FISH to accelerate the procedure. The chromosomal origin, size, and degree of mosaicism of the sSMC then determine the prognosis. We illustrate the effectiveness on 4 prenatally identified de novo mosaic sSMCs derived from chromosomes 13/21, X, 3, and 17. Three sSMC carriers had a good prognosis and apparently healthy children were born, showing no abnormality till the last examination at the age of 4 years. One case had a poor prognosis, and the parents decided to terminate the pregnancy. Our work contributes to the laboratory and clinical management of prenatally detected sSMCs. FISH is a reliable method for fast sSMC evaluation and prognosis assessment; it prevents unnecessary delays and uncertainty, allows informed decision making, and reduces unnecessary pregnancy terminations.

A girl with neurofibromatosis type 1, atypical autism and mosaic ring chromosome 17.

We describe a girl with neurofibromatosis type 1 (NF1), mild dysmorphic features, growth and mental retardation, autism, and mosaicism of ring chromosome 17 and chromosome 17 monosomy. The extent of genetic material deleted from the ring chromosome was determined using a combination of classical cytogenetics, fluorescence in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA) to be 0.6-2.5 Mb on 17p, and up to about 10 Mb on 17q. Based on our observations and on a review of the literature we argue that in addition to a universal "ring syndrome" which is based on ring instability and is less specific for the chromosome involved, various ring chromosomes underlie their own characteristic phenotypes. We propose that the symptoms leading to the diagnosis of NF1 in our patient could be attributed to mosaic hemizygosity for the NF1 gene in some of her somatic cells. A similar mechanism or a direct involvement of respective disease genes in the aberration could possibly influence also the development of autism and other symptoms. We raise a question if the loss of one copy of chromosome 17 from a substantial fraction of somatic cells can have specific consequences also for future risks of the patient, for example, due to the mosaic hemizygosity for the BRCA1 and TP53 genes.

Prader-Willi syndrome due to uniparental disomy in a patient with a balanced chromosomal translocation.

OBJECTIVES: In contrast to most human autosomal genes which are expressed biallelically, the expression of imprinted genes depends on the parental origin of the allele. Prader-Willi syndrome is a neurobehavioral disorder in which the expression of active paternal alleles of imprinted genes from chromosomal region 15q11-q13 is abolished by deletions, maternal uniparental disomy or imprinting defects. We report an unusual case of maternal uniparental disomy of chromosome 15 due to a balanced translocation t(8;15)(q24.1;q21.2) leading to Prader-Willi syndrome in a 3-year-old girl. METHODS AND RESULTS: Cytogenetic investigation revealed a balanced translocation t(8;15)(q24.1;q21.2) in the patient and subsequently also in her unaffected mother. Fluorescence in situ hybridization analysis did not reveal any deletion of the PWS critical region, but methylation analysis of the SNRPN gene showed an abnormal methylation pattern indicating the absence of paternal chromosome 15. Microsatellite analysis of multiple loci and methylation-specific MLPA analysis confirmed maternal uniparental heterodisomy of chromosome 15 as the cause of PWS in the patient. CONCLUSIONS: This example emphasizes the importance of uniparental disomy testing in pregnancies of carriers of chromosomal aberrations with participation of chromosomes carrying imprinted genes involved in human diseases.

Early development of immunity in diGeorge syndrome.

BACKGROUND: diGeorge syndrome is a relatively common congenital disorder with developmental defects, including hypoplasia or pathologic migration of the thymus, associated with deletion of contiguous genes on chromosome 22. We prospectively followed a cohort of children with confirmed 22q11.2 deletion. MATERIAL/METHODS: One to six repeated examination were performed in 13 boys and 21 girls, age 4 days to 19 years. Due to the proposed role of the thymus in T lymphocyte selection, we studied T lymphocytes and their function, and also the presence of double positive CD4+CD8+ and gamma/delta T lymphocytes in peripheral blood. RESULTS: A low number of T lymphocytes was detected in the majority of patients before the age of 2 years. Both spontaneous and PHA-induced proliferation were unexpectedly higher than in normal samples from children <2 years old. Both T cell numbers and function normalized thereafter in the majority of patients. Double positive T cells were detected in one boy, together with transient positivity of antinuclear antibodies. Gamma/delta T cells were greater than 5% in 21% of the children. In our 5-year prospective study we have not yet observed serious clinical signs of immunodeficiency or autoimmunity in these patients, except for repeated respiratory infections. CONCLUSIONS: All patients classified as partial diGeorge syndrome presented with delayed but gradual development of immune function against a background of impaired support by the thymus.

DiGeorge/velocardiofacial syndrome: FISH studies of chromosomes 22q11 and 10p14, and clinical reports on the proximal 22q11 deletion.

DiGeorge anomaly/velocardiofacial syndrome (DG/VCFS) occurs with different deletion intervals on chromosomes 22q11, while the DiGeorge anomaly (with other findings) is seen in patients with deletions of 10p14. The clinical outcome with the common 22q11 deletion (90% of cases) is well known, but the outcome with the less frequent deletion types has not been well documented. Using cytogenetic and fluorescence in situ hybridization (FISH) analysis we studied a series of 295 patients with suspected DG/VCFS. We identified 58 subjects with a 22q11 deletion, and none with a 10p deletion. Fifty-two subjects had the common deletion, five had the proximal deletion, and one had an atypical proximal deletion due to a 1;22 translocation. We report clinical data of four subjects with the proximal 22q11 microdeletion, and of one patient with the atypical proximal deletion. The anomalies observed with the proximal 22q11 microdeletion fell within the DG/VCFS spectrum. Two females, 6 and 25 years old, had normal mental development. Normal development has been reported with the common 22q11 deletion, but only in a minority of cases. This study may indicate a better intellectual and/or behavioral outcome with the proximal vs. the common 22q11 deletion, rather than a chance finding.