Tetrasomy 9p caused by idic (9) (pter----q13----pter)

A Systematic Clinical Review of Prenatally Diagnosed Tetrasomy 9p

Tetrasomy 9p was first described in 1973 and approximately 68 cases with a variable phenotype have been reported to date with 22 of them being detected prenatally. The objective of this study was to review prenatally-reported cases of tetrasomy 9p thus far and to identify ultrasound phenotypes that may be suggestive of this specific syndrome. A PubMed database search was done in February 2018 without any restriction of publication date orjournals, with the use of the following keywords: tetrasomy 9p, tetrasomy 9p prenatal, mosaic tetrasomy 9p, mosaic tetrasomy 9p prenatal, isochromosome 9p, duplication 9p prenatal, trisomy 9p prenatal. Reported cases were included if the clinical presentation and diagnostic approach of each case was clearly described. The most common characteristics of prenatally-detected tetrasomy 9p are intrauterine growth retardation (IUGR, 57.0%), central nervous system (CNS) abnormalities (59.0%), skeletal anomalies (29.0%), genitourinary and renal anomalies (29.0%) and cardiac defects (29.0%). The phenotypic spectrum of tetrasomy 9p is rather unspecific as these findings are commonly associated with other chromosome anomalies, as well as microdeletion/microduplication or monogenic syndromes. The combination of early fetal morphology and diagnostic genetic testing enables a definite tetrasomy 9p diagnosis and effective further pregnancy management.

Clinical and molecular delineation of Tetrasomy 9p syndrome: report of 12 new cases and literature review

Tetrasomy 9p is a generic term describing the presence of a supernumerary chromosome incorporating two copies of the 9p arm. Two varieties exist: isodicentric chromosome 9p (i(9p)), where the two 9p arms are linked by a single centromeric region, and pseudodicentric 9p (idic(9p)), where one active and one inactive centromere are linked together by a proximal segment of 9q that may incorporate euchromatic material. In living patients, i(9p) and idic(9p) are usually present in a mosaic state. Fifty-four cases, including fetuses, have been reported, of which only two have been molecularly characterized using array-CGH. Tetrasomy 9p leads to a variable phenotype ranging from multiple congenital anomalies with severe intellectual disability and growth delay to subnormal cognitive and physical developments. Hypertelorism, abnormal ears, microretrognathia and bulbous nose are the most common dysmorphic traits. Microcephaly, growth retardation, joint dislocation, scoliosis, cardiac and renal anomalies were reported in several cases. Those physical anomalies are often, but not universally, accompanied by intellectual disability. The most recurrent breakpoints, defined by conventional cytogenetics, are 9p10, 9q12 and 9q13. We report on 12 new patients with tetrasomy 9p (3 i(9p), 8 idic(9p) and one structurally uncharacterized), including the first case of parental germline mosaicism. All rearrangements have been characterized by DNA microarray. Based on our results and a review of the literature, we further delineate the prenatal and postnatal clinical spectrum of this imbalance. Our results show poor genotype-phenotype correlations and underline the need of precise molecular characterization of the supernumerary marker.

Replication error, a new hypothesis to explain the origin of a supernumerary marker chromosome in a mentally retarded boy

A marker chromosome present in all the lymphocytes of a mentally retarded boy (47,XY,+mar) was identified. The karyotype of all fibroblasts was normal, 46,XY. His parents had normal karyotypes. The supernumerary marker chromosome was interpreted as a dicentric palindromic chromosome iso(9) (pter----q12, q12----pter). The marker chromosome may have originated through a ligation error in a replication fork during the S-phase followed by a new replication (endoreduplication).

Two cases of tetrasomy 9p syndrome with tissue limited mosaicism

Tetrasomy of short arm of chromosome 9 constitutes a clinically recognizable chromosomal syndrome. Isochromosome 9p shows a strong propensity to tissue-limited mosaicism. It occurs predominantly in peripheral blood cultures, often at a lower frequency or even absent in skin, amniotic fluid or chorionic villous cell cultures. Tissue-limited nature of mosaicism may render prenatal detection of this condition very difficult. Herein, we report two new cases of mosaic tetrasomy 9p. Conventional cytogenetics (CC) and FISH studies demonstrated a differential expression of the mosaicism in several tissues. We review the literature and discuss the implications of these findings in cytogenetic prenatal diagnosis.

New case of non-mosaic tetrasomy 9p in a severely polymalformed newborn girl

BACKGROUND

The phenotypic expression of an additional chromosome 9 causes a very broad clinical spectrum of anomalies. The prognosis for infants with non-mosaic tetrasomy 9p is poor, and they usually die at a very early age.

CASE

In this article we present a new case of complete tetrasomy 9p in a newborn girl with multiple dysmorphologic features. Cytogenetic studies were carried out by CBG, GTG, and QFQ chromosome bandings, as well as by fluorescence in situ hybridization (FISH). The cytogenetic findings for the newborn girl showed an extra chromosome interpreted as an isochromosome 9p. The karyotype was characterized as 47,XX,+mar.ish i(9)(p10)(wcp9+). The parental chromosomes were normal.

CONCLUSIONS

The karyotype and clinical features of the newborn girl (e.g., typical craniofacial dysmorphism, severe skeletal anomalies, and visceral and genito-urinary malformations), compared with cases reported in the literature, give additional support to a clinical definition of this chromosomal syndrome.

Three cases of tetrasomy 9p

We report three cases of tetrasomy 9p, two of which were confirmed prenatally. All three had characteristic findings on ultrasound and at birth. We also present a review of the literature, which suggests that a recognizable phenotype for this condition is emerging. Common findings on prenatal ultrasound include intrauterine growth restriction, ventriculomegaly, cleft lip or palate, and renal anomalies. These findings can provide a clue toward the prenatal diagnosis of this condition. There is also a clearly recognizable phenotype at birth. Facial characteristics include hypertelorism, broad nasal bridge/bulbous or beaked nose, cleft lip/palate, ear anomalies, and micrognathia. The exact extent of the isochromosome does not seem to predict severity, but mosaic cases are less severe, or at least have a greater probability of survival.

Tetrasomy 9p due to an intrachromosomal triplication of 9p13-p22

To date, approximately 30 patients have been described with a tetrasomy 9p, all being caused by the presence of an isochromosome 9p. We now report on a 3-year-old boy with a de novo intrachromosomal triplication of 9p13-p22, resulting in partial tetrasomy 9p. We compared his phenotype with cases of tetrasomy 9p caused by the presence of an extra isochromosome 9p. He has facial anomalies similar to those of cases of tetrasomy 9p, central nervous system abnormalities, and severe psychomotor retardation but no other major congenital anomalies. Fluorescence in situ hybridization with region-specific probes showed that the middle repeat of the triplicated part is inverted. Microsatellite analysis demonstrated an involvement of both paternal chromosome 9 homologues in the triplication. This is compatible with either unequal crossing over of three of the four chromatids in paternal meiosis I or with a double crossing over in meiosis I and II (or an early mitotic division).

Prenatal identification of de novo marker chromosomes using micro-FISH approach

Chromosome microdissection combined with polymerase chain reaction (PCR) and reverse chromosome painting ('micro-FISH') is a powerful technique for the unequivocal identification of complex or subtle chromosomal aberrations. We have applied this technique to the prenatal diagnosis of three fetuses with de novo marker chromosomes. One small supernumerary satellited marker chromosome was shown to have originated from the fusion of the centromeric heterochromatin of one or both of chromosomes 14 and 22. The second marker was identified as i(9)(p10) while the third marker chromosome was shown to have been derived from the 1p13.1-1q21.3 region. At birth, the clinical outcome correlated well with that expected from the prenatal cytogenetic findings. Our study highlights the importance of the application of 'micro-FISH' to prenatal diagnosis.

Moving towards a syndrome: a review of 20 cases and a new case of non-mosaic tetrasomy 9p with long-term survival

Tetrasomy 9p is a rare syndrome that has now been described in nearly a score of cases. We present a new case of i(9p) that presented to us early in infancy with significant dysmorphological features, including growth retardation, psycho-motor delay, hemifacial microsomia, auditory canal atresia, high-arched palate, bulbous nose, strabismus, epicanthic folds, congenital heart disease, dislocated hips, hypoplastic external genitalia, simian palmar creases, dysplastic nails and small digits. Chromosomal analysis revealed a 47,XX,idic(9)(q12) karyotype on GTG- and C-banding studies on peripheral blood lymphocytes. Fluorescent in situ hybridization (FISH) studies confirmed the origin of the extra chromosome. A review of the literature and a comparative analysis of the several well-documented cases of i(9p) revealed a pattern of recurring features, including ear malformations, skeletal and joint problems (especially dislocations), hypoplasia of nails and digits, palatal abnormalities, hypertelorism, urogenital anomalies and developmental retardation. In the light of this analysis, we feel that tetrasomy 9p will soon be considered a clinically recognizable syndrome.

Non-mosaic tetrasomy 9p in a liveborn infant with multiple congenital anomalies: case report and comparison with trisomy 9p

Tetrasomy of the short(p) arm of chromosome 9 has been reported in few cases. Most of these children present with microbrachycephaly, wide forehead, hypertelorism, lowset, malformed ears, beaked noses, and micrognathia. Additional anomalies include short neck, congenital heart disease, genital abnormalities, multiple limb defects, hypotonia, and early death.

Duplication of 9P and hyperplasia of the choroid plexus: a pathologic, radiologic, and molecular cytogenetics study

Duplication of the short arm of chromosome 9 is a rare constitutional abnormality, and the presence of pathologically confirmed hyperplasia of the choroid plexus in one of two cases, and a choroid plexus papilloma in another, raises the possibility of a relationship between the 9p abnormality and abnormal growth of the choroid plexus. Molecular cytogenetic analysis using fluorescence in situ hybridization was used for detection of chromosome 9-derived material in various formalin-fixed choroid plexus abnormalities. Extra copies of chromosome 9-derived material was found in the hyperplastic choroid plexus and in a choroid plexus carcinoma. These findings suggest that there may be an association between duplication of chromosome 9 material and abnormal development of the choroid plexus.

A case of tetrasomy 9p

A case of mosaic 9p tetrasomy (46,XX/47,XX, + dic[9] [q21]) is reported. Clinical manifestations of the patient were generalized hypotonia, severe mental retardation and characteristic dysmorphic features of 9p tetrasomy. A brief review of the literature is also included.

Syndactyly, ectodermal dysplasia, and cleft lip/palate

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Tetrasomy 9p: tissue-limited idic(9p) in a child with mild manifestations and a normal CVS result. Report and review

Supernumerary isochromosomes resulting in autosomal tetrasomy are rare and have been described only for 12p, 18p, and 9p. Nineteen previous cases of tetrasomy 9p have been reported, and in 6 cases, tissue-specific mosaicism was implied with the i(9p) cell line present exclusively or predominantly in blood. We report on an infant who had apparently normal chromosomes (46,XY) on CVS. He was referred for genetic evaluation because of mild developmental delay and minor anomalies. In 75% of blood cells he had an extra isodicentric 9p chromosome (pter-->q12-->pter). The interpretation of tetrasomy 9p was confirmed by elevated GALT activity. No tetrasomy 9p cells were seen in 100 skin fibroblasts. This case demonstrates the tissue specific mosaicism in tetrasomy 9p which rendered the anomaly undetectable by CVS. It also demonstrates the mild end of the clinical spectrum associated with tetrasomy 9p.

Tetrasomy of the short arm of chromosome 9: prenatal diagnosis and further delineation of the phenotype

A fetus with multiple malformations was identified by prenatal ultrasound investigation. Cordocentesis and fetal lymphocyte chromosome analysis demonstrated a model number of 47 chromosomes. The extra chromosome material was identified as an isochromosome of the entire short arm of chromosome 9 with no involvement of the heterochromatic region of the long arm [47,XY, + i(9p)]. This represents the first report of prenatal diagnosis of tetrasomy 9p. Further delineation of the phenotype is discussed.

Tetrasomy 9p: an emerging syndrome

An infant with non-mosaic 9p tetrasomy is described. The tetrasomy apparently results from a translocation involving the 9qh region. All the cells analyzed from multiple banding techniques from lymphocyte culture as well as skin fibroblast culture were 9p tetrasomic. The infant, who had the characteristic dysmorphic features of 9p tetrasomy, survived for 2 months. Prominent features included: low birth weight, severe retardation, brachycephaly with large anterior fontanelle, hypertelorism with short bilateral palpebral fissures, beaked nose, bilateral cleft lip and palate, and low-set, malformed ears. Skeletal anomalies, ambiguous genitalia and heart defect were also observed. These features are highly characteristic of the 9p tetrasomy syndrome based on six pure tetrasomy and four cases of tetrasomy that included part of the 9qh region.

Tissue limited mosaicism in a patient with tetrasomy 9p

Cytogenetic analysis of an abnormal newborn girl showed an extra chromosome with the characteristics of an isodicentric 9p chromosome [idic (9)(pter----q12----pter)] in 98% of peripheral lymphocyte metaphases examined. This cytogenetic interpretation was substantiated by quantitative measurement of erythrocyte galactose-1-P-uridyltransferase (GALT) activity, which is consistent with the expression of 4 normal GALT genes. Cytogenetic results from skin fibroblasts showed mosaicism with only 11% of the metaphases having the extra chromosome. Selective genetic pressure based on a functional disadvantage of tetrasomy 9p in the skin is proposed. The in vivo establishment of cytogenetically normal cells in various tissues may be necessary for in utero survival of tetrasomy 9p infants.

Prenatal diagnosis of a case of tetrasomy 9p

A male fetus with tetrasomy 9p [47,XY, + i(9p)] is presented. The cytogenetic interpretation of the marker chromosome was confirmed by assessing the activity of the enzyme galactose I-phosphate uridyl transferase. The clinical findings of the case show features in common with previously reported cases.

Partial tetrasomy 9 in an infant with clinical and radiological evidence of multiple joint dislocations

We report on an infant with partial tetrasomy of chromosome 9 due to the presence in her peripheral lymphocytes and in 55% of skin fibroblasts of an isochromosome 9 comprised of the p arm and of a portion of the q arm extending to band q21.1. The phenotype is comparable to that of other cases with a similar chromosome aberration, with multiple joint dislocations as a prominent manifestation.