Mosaic 5p tetrasomy

Cytogenomic characterization of small supernumerary marker chromosomes in patients with pigmentary mosaicism

Introduction

The combination of gene content on the marker chromosome, chromosomal origin, level of mosaicism, origin mechanism (chromothripsis), and uniparental disomy can influence the final characterization of sSMCs. Several chromosomal aberrations, including sSMCs, have been observed in 30%-60% of patients with pigmentary mosaicism, and in more than 80%, chromosomal abnormalities are present in the mosaic state. In patients with pigmentary mosaicism the most representative chromosomes involved in sSMCs are 3, 5, 6, 9, 10, 13, 15, 18, 20, and X. In this study, we included the complete clinical, cytogenetic, and molecular characterization of seven patients with pigmentary mosaicism associated with the presence of SMCs of different chromosomal origins.

Methods

The patients were diagnosed by the Genetics and Dermatology Department of three different hospitals. Cytogenetic and FISH analyses were performed on peripheral blood, light skin, and dark skin. FISH analysis was performed using different probes, depending on the marker chromosome description. Different array analysis was performed.

Results

To date, of the seven cases studied, the chromosomal origins of six were successfully identified by FISH or array analysis. The chromosomes involved in SMCs were 6, 9, 15, and 18, X. The most frequently found was the centric minute structure.

Discussion

To date, this group of seven patients constitutes the largest clinical and cytogenetically finely described study of cases with pigmentary mosaicism associated with sSMCs. Undoubtedly, analysis of the two skin types is a fundamental part of our study, as numerical differences may occur in the cell lines found in each skin type. The knowledge generated in this study will help delineate a very heterogeneous entity more accurately, and in the future, analyzing more patients with PM will likely establish a more definite association with the presence of this genetic alteration.

Diagnosis and clinical delineation of mosaic tetrasomy 5p

OBJECTIVE

Our objective was to review the phenotypic and genetic characteristics of tetrasomy 5p from the fetal period until adulthood including prenatal diagnostic evaluations.

BACKGROUND

Tetrasomy 5p is a rare chromosomal abnormality. Of the 14 reports, most document mosaic tetrasomy 5p resulting from a supernumerary marker chromosome or isochromosome. There is a wide range of phenotypic manifestations with severity related to more proximal breakpoints and the degree of mosaicism.

DESIGN

We conducted a systematic review using Scopus, PubMed Central® and Ovid MEDLINE® from inception through July 1, 2018 for all articles describing tetrasomy 5p. All articles describing the syndrome of tetrasomy 5p were included.

RESULTS

Of the 15 included cases, 13 exhibited mosaic tetrasomy and two had complete tetrasomy identified by amniocentesis. The most common features include seizures (8/11 live births, 73%), hypotonia (7/11 live births, 64%), developmental delay (7/9 cases that reached childhood, 78%), abnormal external ears (6/11 live births, 55%), short stature (6/11 live births, 55%), ventriculomegaly (5/11 live births, 45.5%) and congenital heart defect (6/15 cases, 40%). The clinical phenotype ranged in severity from mild with no defining characteristics to severe with seizures, developmental delay, and multiple congenital anomalies, resulting in early death. Of these 15 cases, only 6 were diagnosed prenatally by prenatal genetic testing (40%) with prenatal ultrasound identifying abnormalities in 4/6 (67%). Confined placental mosaicism (CPM) was diagnosed in six additional cases due to discordance between CVS and amniocentesis results. Four of the five live births returned for evaluation and each showed normal development.

CONCLUSIONS

Fourteen out of 15 (93%) cases of tetrasomy 5p were associated with an abnormal phenotype. Once a diagnosis is made prenatally, a detailed anatomy ultrasound and fetal echocardiogram must be performed to further characterize any structural abnormalities of the fetus and potentially estimate the clinical severity. Caution should be exercised when prenatal diagnosis of mosaic tetrasomy 5p is found by chorionic villus sampling. CVS alone is insufficient to diagnose tetrasomy 5p and needs to be confirmed with amniocentesis. Our review seeks to inform clinicians on the current literature regarding tetrasomy 5p so that they may better counsel patients when this syndrome is diagnosed.

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.

Electronic supplementary material

The online version of this article (10.1186/s13039-018-0377-1) contains supplementary material, which is available to authorized users.

Small supernumerary marker chromosomes and their correlation with specific syndromes

A small supernumerary marker chromosome (sSMC) is a structurally abnormal chromosome. It is an additional chromosome smaller than one chromosome most often lacking a distinct banding pattern and is rarely identifiable by conventional banding cytogenetic analysis. The origin and composition of an sSMC is recognizable by molecular cytogenetic analysis. These sSMCs are seen in different shapes, including the ring, centric minute, and inverted duplication shapes. The effects of sSMCs on the phenotype depend on factors such as size, genetic content, and the level of the mosaicism. The presence of an sSMC causes partial tris- or tetrasomy, and 70% of the sSMC carriers are clinically normal, while 30% are abnormal in some way. In 70% of the cases the sSMC is de novo, in 20% it is inherited from the mother, and in 10% it is inherited from the father. An sSMC can be causative for specific syndromes such as Emanuel, Pallister-Killian, or cat eye syndromes. There may be more specific sSMC-related syndromes, which may be identified by further investigation. These 10 syndromes can be useful for genetic counseling after further study.

Altered DNA copy number in patients with different seizure disorder type: by array-CGH

Epilepsy is one of the most common but genetically complex neurological disorders in children. Previous studies have showed that chromosomal abnormalities confer susceptibility to epilepsy. To identify new chromosomal abnormalities associated with epilepsy, DNA samples from patients with idiopathic generalized epilepsy (IGE), partial epilepsy (PE), and febrile seizures (FS) were analyzed using array comparative genome hybridization technique (array-CGH). Genomic aberrations were detected throughout whole chromosome. The most frequently altered loci were gains noted in: 1p (60%), 5p (55%), 8q (55%), 10q (55%), and losses in 7q (55%). The most frequent chromosomal aberrations for each seizure type were: IGE-1p (60%), 5p (55%), and 10q (55%), PE-11p (45%), 21q (45%) and FS-8q (55%), and losses in 7q (55%). To validate the array-CGH results, real time PCR was performed for several genes (EPM2AIP1, OSM, AFP, CYP19A1, SLC6A13, and COL6A2). The results from the real time PCR were consistent with those from the array-CGH. Therefore, we found that the three types of seizures disorder studied have different chromosomal aberrations. These results might be used for further investigation of the pathogenesis of epilepsy.

Abnormal pigmentation in hypomelanosis of Ito and pigmentary mosaicism: the role of pigmentary genes

There is increasing evidence that hypomelanosis of Ito and related disorders such as linear and whorled naevoid hypermelanosis are due to mosaicism for a variety of chromosomal abnormalities. This group of disorders is better termed 'pigmentary mosaicism'. In this review we explain how disparate chromosomal abnormalities might manifest as a common pigmentary phenotype. In particular, we provide evidence supporting the hypothesis that the chromosomal abnormalities reported in these disorders specifically disrupt expression or function of pigmentary genes.

Pigmentary mosaicism with mosaic chromosome 5p tetrasomy

Pigmentary mosaicism with mosaic chromosome 5p tetrasomy is described. A 5-year-old girl had phylloid hyperpigmentation segregated in the midline, and neurological deficits. Chromosome analysis performed on blood lymphocytes was normal, whereas skin fibroblasts from affected skin areas revealed chromosomal mosaicism.

Isochromosome 5p mosaicism at prenatal diagnosis: observations and outcomes in six cases at chorionic villus sampling and one at amniocentesis

We present six cases of 47,+i(5p)/46 mosaicism diagnosed at chorionic villus sampling (CVS), this being the first prospective series to be reported. The clinical indication in each was advanced maternal age. Further prenatal studies in four (amniocentesis, plus fetal blood sampling in one) did not show the isochromosome. In one case, subsequent amniocentesis showed 1/48 in situ colonies with the isochromosome, but fetal blood was karyotypically normal. These five pregnancies resulted in phenotypically normal livebirths; further normal follow-up reports (from age 4 months through 4 years) are noted in four of these. Analysis of placental tissue in one case confirmed the presence of the i(5p) mosaicism. In the remaining case, in which 100% of CVS cultured cells had the i(5p), the pregnancy was terminated. Fetal skin fibroblasts did not show the i(5p). Thus, in none of these six cases was true fetal mosaicism detected, nor an abnormal phenotype noted. We suggest that a 47,+i(5p)/46 karyotype, detected at CVS, may frequently reflect confined placental mosaicism. In addition, we report a case of the primary diagnosis of 47,+i(5p)/46 mosaicism at amniocentesis. The infant appeared normal at birth, but a brain malformation was subsequently identified.

Prenatal diagnosis of mosaic tetrasomy 5p

We report the prenatal diagnosis of a fetus with tetrasomy 5p mosaicism resulting from a supernumerary isochromosome for the short arm of chromosome 5. The pregnancy was terminated and fetal autopsy revealed minor facial abnormalities (long philtrum, up-slanting palpebral fissures and a broad nasal bridge). Cultures were established from fetal skin, kidney, and pancreas for cytogenetic analysis; the i(5p) was observed only in the skin fibroblasts. To our knowledge, this is the fourth report of mosaic tetrasomy 5p and the first report of prenatal diagnosis of this abnormality.

MRI findings in a patient with partial monosomy 10p

Partial monosomy 10p is a rare chromosomal disorder characterised by frontal bossing, micrognathia, congenital heart defects, vesicoureteral abnormalities, and developmental delay. This is the first report to describe seizures not associated with hypocalcaemia, as well as cortical atrophy and decreased white matter volume on magnetic resonance imaging, in a patient with documented partial monosomy 10p. The neuroradiographic abnormalities found in this patient provide a first step towards understanding the aetiology of the developmental delay and ventriculomegaly associated with this chromosomal abnormality.

Linear hypopigmentation and hyperpigmentation, including mosaicism

Linear streaks of hypopigmentation or hyperpigmentation along Blaschko's lines are currently grouped under the names hypomelanosis of Ito (HI) and linear and whorled hypermelanosis (LWH). Recent studies have suggested that these linear pigmentary anomalies reflect underlying genetic mosaicism. Mosaic individuals are composed of two or more genetically distinct cell populations, a normal and an abnormal population. In HI and LWH, the types of genetic defects that are detectable in the abnormal population are highly variable, including tetraploidy, partial or complete trisomies, translocations, and point mutations. These results, together with recent studies indicating the incidence of extracutaneous anomalies is lower in HI but higher in LWH than previously estimated, have important clinical implications. The need for a revised nomenclature as well as possible modifications in current recommendations for patient management are 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.

Mosaic tetrasomy 15q25-->qter in a newborn infant with multiple anomalies

We describe a premature boy with metopic craniosynostosis, facial anomalies, atrial-septal defect, hydronephrosis and flexion contractures of lower limbs, and mosaic tetrasomy 15q25-->qter. The extra chromosome material was present in the form of an acentric marker. A number of clinical manifestations observed in this child were also found in 3 previously reported patients who were trisomic for the same part of chromosome 15 and in 2 patients who were tetrasomic for a larger segment of 15q.

Asymmetry and skin pigmentary anomalies in chromosome mosaicism

We report six persons mosaic for a chromosome anomaly. All were mentally retarded and dysmorphic. Unilateral or asymmetrical features were found in all cases, in one an unusual transverse terminal limb anomaly, and in the others various degrees of hemiatrophy of the left side of the body. Five of the subjects had skin pigmentary anomalies which were distributed in the lines of Blaschko. The abnormal cell lines found were ring chromosome 22, trisomy 22, a large acrocentric marker, a deletion of 18q, a deletion of 8q, and triploidy. In four cases the clinical diagnosis was only confirmed by skin biopsy. In one case low level mosaicism in blood was fortuitously detected because of cytogenetic fragile X screening and confirmed in a skin biopsy. The sixth case was of dynamic mosaicism of a non-mosaic deletion 18q with a chromosome 18 derived marker present in a proportion of cells. Chromosome mosaicisn may cause subtle and asymmetrical clinical features and can require repeated cytogenetic investigations. The diagnosis should be actively sought as it enables accurate genetic counselling to be given.

Mosaicism with a normal cell line and an autosomal structural rearrangement

Over three decades, 12 cases of mosaicism for an autosomal rearrangement were recognised in the major cytogenetics laboratories in New Zealand, eight of which were studied between 1990 and 1992. One case inferentially involved the gonad, eight the soma, and three both gonad and soma. This mosaicism could have arisen as a postzygotic event either in a conceptus that was initially normal, with the generation of an abnormal cell line, or in a conceptus having a supernumerary chromosome which was lost at a subsequent mitosis, thereby restoring a normal cell line. Three of the 12 cases involved a presumed direct duplication, an otherwise very uncommon rearrangement. This may indicate a propensity for direct duplications to arise at mitosis rather than at meiosis; unequal sister chromatid exchange is a plausible mechanism. Mosaicism has clinical relevance for genetic counselling, as an intragonadal cell line carrying a rearrangement could generate multiple unbalanced gametes. Mosaicism for an autosomal rearrangement my be very much more common that is, or ever could be, recognised.

Tetrasomy 5p mosaicism in a boy with delayed growth, hypotonia, minor anomalies, and an additional isochromosome 5p [46,XY/47,XY, + i(5p)]

We describe a 1-year-old boy with a rare de novo 46,XY/47,XY, + i(5p) mosaicism (ratios 28/3 in peripheral blood lymphocytes and 2/12 in skin fibroblasts). The boy, born after a pregnancy of 34 weeks, had lung hypoplasia, persistent hypotonia, and postnatal growth failure. Craniofacial anomalies were also present. His clinical manifestations correspond to those described in trisomy 5p patients. Prenatal diagnosis on maternal age indication had shown normal male chromosomes in 16 cells in the short term culture of a chorionic villus sampling. Retrospectively, 1 out of 217 cells in this culture showed the i(5p). Several mechanisms could have resulted in the formation of this 46/47, + i(5p) mosaic. Postzygotic local incorrect ligation during chromatid replication, followed by a second replication offers an attractive model on theoretical grounds since it needs only one step to explain both isochromosome formation and mosaicism. Differences between the various tissues in selection pressure on cells with the isochromosome might explain the different ratios of mosaicism found.