Familial partial trisomy 5p resulting from segregation of an insertional translocation

Whole-genome array CGH identifies pathogenic copy number variations in fetuses with major malformations and a normal karyotype

Despite a wide range of clinical tools, the etiology of mental retardation and multiple congenital malformations remains unknown for many patients. Array-based comparative genomic hybridization (aCGH) has proven to be a valuable tool in these cases, as its pangenomic coverage allows the identification of chromosomal aberrations that are undetectable by other genetic methods targeting specific genomic regions. Therefore, aCGH is increasingly used in clinical genetics, both in the postnatal and the prenatal settings. While the diagnostic yield in the postnatal population has been established at 10-12%, studies investigating fetuses have reported variable results. We used whole-genome aCGH to investigate fetuses presenting at least one major malformation detected on ultrasound, but for whom standard genetic analyses (including karyotype) failed to provide a diagnosis. We identified a clinically significant chromosomal aberration in 8.2% of tested fetuses (4/49), and a result of unclear clinical significance in 12.2% of tested fetuses (6/49). Our results document the value of whole-genome aCGH as a prenatal diagnostic tool and highlight the interpretation difficulties associated with copy number variations of unclear significance.

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 approximately 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.

De novo complete trisomy 5p: clinical and neuroradiological findings

Partial or complete duplication of 5p is a rare chromosomal abnormality in which genotype-phenotype correlation studies are hampered by other commonly associated chromosomal abnormalities. We report on a new patient in whom a complete de novo trisomy 5p in all metaphases represented the only chromosomal aberration. The present case further contributes to delineate the typical clinical picture of the trisomy 5p syndrome. Long-term clinical follow-up demonstrated low levels of secretory immunoglobulin A (IgA) on several occasions and likely related to the patient's recurrent respiratory infections (RRIs), a main clinical feature of the trisomy 5p syndrome. An extensive neuroradiological study detected a progressive triventricular hydrocephalus during the fist year of life with subsequent stabilization. Neuronal migration disorders were also present and probably account for the drug-resistant epilepsy presented by the patient.

Supernumerary marker chromosomes 5: confirmation of a critical region and resultant phenotype

A critical region exists at 5p13 for the phenotype associated with duplication 5p. Two unrelated Polynesian children are reported with supernumerary marker chromosomes (SMCs) 5. This brings to seven the total of reported SMCs derived from chromosome 5. The phenotype is clear, and the level of mosaicism of the marker chromosomes is contributory to the clinical severity.

Tertiary trisomy due to a reciprocal translocation of chromosomes 5 and 21 in a four-generation family

Tertiary trisomy, or double trisomy, is a rare occurrence. We present two individuals with a previously unreported tertiary trisomy for chromosomes 5p and 21q in an eight-generation pedigree. Their phenotypes are compared with other partial trisomies of either 5p or 21q from the literature. The propositus was diagnosed with trisomy 21 at 2 years of age after a karyotype study for short stature and developmental delay. His phenotype was described as atypical for Down syndrome. He presented at 9 years of age because of pervasive behavioral problems and obesity. He was brachycephalic with a flattened nasal bridge, but he lacked other characteristics of trisomy 21. Because of lack of phenotypic evidence of Down syndrome, a repeat karyotype was obtained and showed 47,XY, +der(21)t(5;21)(p15.1; q22.1), incorporating partial trisomies of both chromosomes 5 and 21. Mother had a balanced translocation, 46, XX,t(5;21)(p15.1; q22.1); 8 other relatives were examined. The translocation originated from the maternal great-grandmother, but only the propositus and his mentally retarded aunt had a similar phenotye and the derivative chromosome. Fluorescence in situ hybridization showed absence of band 21q22.2 in the derivative chromosome of the propositus and his aunt, indicating that neither had trisomy for the Down syndrome critical region. These cases represent a unique double partial trisomy of chromosome arms 5p and 21q that occurred because of 3:1 malsegregation of a reciprocal translocation. These cases further demonstrate that phenotypic discordance with cytogenetic results dictate further investigation using advanced cytogenetic hybridization.

Identification of supernumerary marker chromosomes derived from chromosomes 5, 6, 19, and 20 using FISH

A large number of cases with supernumerary marker chromosomes (SMCs) should be compared to achieve a better delineation of karyotype-phenotype correlations. Here we present four phenotypically abnormal patients with autosomal marker chromosomes analysed by fluorescence in situ hybridisation using centromeric, telomeric, and unique sequence probes, as well as forward and reverse painting. We also report the first case, to the best of our knowledge, of an SMC derived from chromosome 5. Furthermore, a marker chromosome 20 in a patient with sex differentiation abnormalities, a double mar(6) in a boy with psychomotor retardation, and the association of r(19) with dup(21q21.2q22.12) are described. Although the mar(6) was very small, the presence of euchromatin was shown, suggesting that the partial trisomy of pericentric region derived sequences is implicated in the aetiology of the abnormal phenotypes.

Proximal partial 5p trisomy resulting from a maternal (19;5) insertion

We present a case with a partial duplication 5p11-->5p13.3 resulting from a maternal ins (19,5)(p11;p11-p13.3). The diagnosis was confirmed by FISH and complement component determinations. The clinical picture was similar to those described in patients with complete duplication of the short arm and in some patients with partial 5p duplications, affecting at least band 5p13. A special significance of band 5p13 in the clinical severity of 5p duplications is discussed.

Interstitial deletion 5p accompanied by dicentric ring formation of the deleted segment resulting in trisomy 5p13-cen

Karyotypes with an interstitial deletion and a marker chromosome formed from the deleted segment are rare. We identified such a rearrangement in a newborn infant, who presented with macrocephaly, asymmetric square skull, minor facial anomalies, omphalocele, inguinal hernias, hypospadias, and club feet. The karyotype 46,XY,del(5) (pter --> p13::cen --> qter)/47,XY,+dicr(5)(:p13 --> cen::p13 --> cen), del(5)(pter --> p13::cen --> qter) was identified by banding studies and FISH analysis in the peripheral lymphocytes. One breakpoint on the del(5) maps distal to GDNF, and FISH analysis using an alpha-satellite probe suggests that the proximal breakpoint maps within the centromere. The dicentric r(5) consists of two copies of the segment deleted in the del(5), resulting in trisomy of proximal 5p (5p13-cen). The phenotype of the propositus is compared with other trisomy 5p cases and possible mechanisms for the generation of this unique chromosomal rearrangement are discussed.

Partial trisomy for short arm of chromosome 5

We present two unrelated cases of partial trisomy for the short arm of chromosome 5, the first such cases reported in Japan. The features are characterized by hypertelorism, low set ears, arachnodactyly, laryngostenosis, hypotonia and some cerebral malformation. The characteristic facial expression and arachnodactyly are the key features used to diagnose this disorder. A high-resolution chromosome banding technique showed that the karyotype of the first patient was 46,XX,inv dup(5) (p13.1-->p15.3) de novo and that of the second patient was 46,XX,dir dup(5) (p13.3-->p15.2) de novo. The similar symptoms in the two cases, despite the difference in karyotypes, were caused by duplication of 5p including segment 5p13. This would be a key site for this disorder.

Mosaic 5p tetrasomy

We report on a mildly abnormal 5-year-old girl with seizures, psychomotor retardation, and areas of hyperpigmentation who had a supernumerary marker chromosome in fibroblasts which was identified as an i(5p). To our knowledge, this is the first reported case of tetrasomy 5p. She shares in common some, but not all, manifestations of the dup (5p) syndrome. Cytogenetic analysis of relatives showed that the phenotypically apparently normal mother, maternal grandmother, and a brother of the proband also had a marker chromosome in their lymphocytes which was unrelated to the i(5p).

Apparent Opitz BBBG syndrome with a partial duplication of 5p

We describe a patient with a paracentric inversion and partial duplication of chromosome 5p. In addition this patient presented with a malformation pattern consistent with Opitz BBBG syndrome. This implies that the gene responsible for this single gene defect may be located within this duplicated region.

Pure partial trisomy of the short arm of chromosome 5

We describe a male infant with multiple dysmorphic features who is trisomic for chromosome segment 5p13.32----5p14.2 as a result of recombination aneusomy. His father is a balanced carrier of an inverted insertion of this chromosome segment. The clinical features of this patient are compared with those of other patients with isolated partial 5p trisomy reported in the literature.