Mosaic trisomy 22: A case presentation and literature review of trisomy 22 phenotypes

In a case of mosaic trisomy 22 the trisomic cells were detected primarily in fibroblasts. Results of initial lymphocyte chromosome analysis were normal. However, mosaicism was suspected because the patient had hypomelanosis of Ito, hemiatrophy, failure to thrive, and mental retardation. Mosaicism was confirmed in cultured fibroblasts. Repeat cytogenetic analysis of peripheral blood demonstrated a low level of trisomic metaphase cells, which was confirmed by interphase fluorescent in situ hybridization (FISH) analysis. Molecular studies supported maternal disomy in the child's disomic cells. The phenotype of this condition overlaps that of non-mosaic trisomy 22 chromosome mosaicism in general and to some extent the Ullrich-Turner syndrome phenotype. Improved cytogenetic and molecular techniques now allow better delineation of aneuploidy syndromes. Molecular and FISH studies added information about this case (mosaicism and uniparental disomy) not appreciated by routine cytogenetic analysis of lymphocytes. The detection of low-level mosaicism and/or uniparental disomy in such cases may change the clinical classification and our understanding of pathogenesis and recurrence risk of these disorders. Am. J. Med. Genet. 71:406–413, 1997. © 1997 Wiley-Liss, Inc.     

Isochromosome 22 in trisomy 22 mosaic with five cell lines

This report describes a full-term male infant with trisomy 22 due to an isochromosome 22. Prenatal diagnosis with amniotic fluid showed two cell lines, one with an isochromosome 22 and the other with a deleted isochromosome 22. Subsequent cytogenetic analyses of cord blood, umbilical cord tissue, and placenta revealed additional cell lines. A normal cell line was found in umbilical cord tissue and two of three placental sites. The newborn had numerous dysmorphic features and died within 48 hrs of birth.     

Fryns syndrome phenotype and trisomy 22

Trisomy 22 was detected in a 32-week-old fetus born to an overweight mother with hypertension. Severe intrauterine growth retardation was associated with phenotypic manifestations of Fryns syndrome: diaphragmatic hernia, facial defects, and nail hypoplasia with short distal fifth phalanges. This is the second report of congenital diaphragmatic hernia in trisomy 22. This case demonstrates the importance of karyotyping malformed fetuses or newborns, even if a nonchromosome syndrome seems identifiable on clinical grounds. To date, at least 10 cases of Fryns syndrome have been reported without chromosome analysis. © 1996 Wiley-Liss, Inc.     

Hydrocephalus in an infant with trisomy 22.

We present an infant with true trisomy 22. Mosaicism is ruled out by the finding of a 47,XX, +22 karyotype in all cells analysed originating from two embryonic germ layers. The physical findings are consistent with the previously noted features including developmental delay, ear abnormalities, micrognathia, clefting, and congenital heart disease. The patient is the first described with macrocephaly and hydrocephalus and the second with holoprosencephaly.     

Alterations in thymocyte subpopulations in Down's syndrome (trisomy 21)

To correlate the histologically observed thymic abnormalities with the cellular immunodeficiency found in Down's syndrome (DS), thymus fragments and thymocyte suspensions from 14 noninstitutionalized DS subjects were studied. Histologic examination and immunohistologic studies using an anticluster of differentiation (CD) 1 monoclonal antibody showed a contracted cortex due to cortical thymocyte depletion. When DS unselected thymocytes were phenotyped, a significant reduction of CD3-, CD1-, CD4-, and CD8-positive cells was found as compared to controls. To evaluate if the deficient expression of these markers was due to the reduction of thymocyte subsets identifiable on the basis of their physical properties, we separated DS unselected thymocytes into 10 fractions by continuous Percoll density gradient centrifugation. DS thymuses were almost completely devoid of high density thymocytes. Since in normal thymus, these cells correspond to small CD1+, CD4+, CD8+, and 50% CD3+ cortical thymocytes, their absence may explain the unrestricted reduction of markers on DS unfractionated thymocytes. Furthermore DS thymuses appeared to be enriched in CD1+ first fraction (Fr1) low density thymocytes of the Percoll gradient. Fr1 CD1+ cells constitute the main spontaneously proliferating pool in normal human thymus. When the spontaneous proliferating activity of DS Fr1 was compared to that of the control, a significant reduction was observed. This reduction associated with the absence of high density thymocytes, with the reduction of cells expressing alpha- and beta-chains of the T cell receptor and in conclusion with the lymphocyte depletion, suggests that in DS thymuses there is a deficient expansion of immature T cells resulting in a reduction of the various thymocyte subpopulations, including the thymocyte pool able to differentiate into functionally mature T cells.     

Confirmation of trisomy 22 by trypsin-giemsa staining.

A small-for-dates male infant with mental retardation, microcephaly, malformed ears, preauricular sinuses, epicanthal folds, micrognathia, congenital heart diseases, micropenis, and micropolygyria of the parietal and occipital lobes of the cerebral cortex was shown to have a 47,XY,+22 karyotype by trypsin-giemsa banding. Review of reported cases confirms that there may be distinctive trisomy 22 syndrome.     

Costovertebral dysplasia in a patient with partial trisomy 22

A newborn female presented with costovertebral dysplasia (CVD), subtle facial anomalies, and neonatal respiratory distress. Her karyotype demonstrated a small supernumerary NOR-positive marker that was subsequently identified as del(22)(q11.2). This extra structurally abnormal chromosome was found by DNA microsatellite marker analyses to be derived from a paternal chromosome 22. The child has had severe growth and developmental delay along with pulmonary insufficiency and hypoxia but is presently stable at age 20 months. Findings in our patient correlate with similar observations in children with small markers derived from D/G and D/D translocations reported before banding technology was available. These reports and recent mapping results suggest that a pericentric gene family, distributed on one or more acrocentric chromosomes, may have played a role in the development of the human axial skeleton. Data from additional studies will be needed to confirm or refute this hypothesis.     

Functional neuroanatomy of the primate isocortical motor system

The concept of the primate motor cortex based on the cytoarchitectonic subdivision into areas 4 and 6 according to Brodmann or the functional subdivision into primary motor, supplementary motor, and lateral premotor cortex has changed in recent years. Instead, this cortical region is now regarded as a complex mosaic of different areas. This review article gives an overview of the structure and function of the isocortical part of the motor cortex in the macaque and human brain. In the macaque monkey, the primary motor cortex (Brodmann’s area 4 or area F1) with its giant pyramidal or Betz cells lies immediately anterior to the central sulcus. The non-primary motor cortex (Brodmann’s area 6) lies further rostrally and can be subdivided into three groups of areas: the supplementary motor areas ”SMA proper” (area F3) and ”pre-SMA” (area F6) on the mesial cortical surface, the dorsolateral premotor cortex (areas F2 and F7) on the dorsolateral convexity, and the ventrolateral premotor cortex (areas F4 and F5) on the ventrolateral convexity. The primary motor cortex is mainly involved in controlling kinematic and dynamic parameters of voluntary movements, whereas non-primary motor areas are more related to preparing voluntary movements in response to a variety of internal or external cues. Since a structural map of the human isocortical motor system as detailed as in the macaque is not yet available, homologies between the two species have not been firmly established. There is increasing evidence, however, that a similar organizational principle (i.e., primary motor cortex, supplementary motor areas, dorso- and ventrolateral premotor cortex) also exists in humans. Imaging studies have revealed that functional gradients can be discerned within the human non-primary motor cortex. More rostral cortical regions are active when a motor task is nonroutine, whereas more routine motor actions engage more caudal areas. Accepted: 3 July 2000     

Complex chromosomal rearrangement leading to partial trisomy 22.

We have examined a boy with a peculiar facial appearance and mental retardation. Cytogenetic studies showed 47,XY, monosomy 22, two marker chromosomes, M1 and M2. The karotype is interpreted as functionally partial trisomy 22. Chromosome analyses of both parents and three sibs were normal.     

Familial translocation with partial trisomy of 13 and 22: evidence that specific regions of chromosomes 13 and 22 are responsible for the phenotype of each trisomy.

A newborn infant with clinical and pathological findings typical trisomy 13 and 22 syndromes had an extra chromosome which was a derivative chromosome from maternal balanced translocation affecting Nos. 13 and 22; 47,XY,+der(22),t(13:22)(q22:q12)Mat. The presence of extra specific euchromatic regions of No. 13(13q22 and/or 13q34) and No. 22 (22q11) seem to be responsible for the trisomy 13 and 22 syndromes.     

Origin, prenatal development and structural organization of layer I of the human cerebral (motor) cortex

Summary The composition and structural organization of layer I of the human motor cortex were studied throughout the course of prenatal cortical neurogenesis with the rapid Golgi method. The components of layer I are six. The specific afferents of layer I (primitive corticipetal fibers) and the Cajal-Retzius neurons are its essential intrinsic components, while the apical dendritic bouquets of all pyramidal neurons and the axonic terminations of all Martinotti neurons are its essential extrinsic elements. These four components are recognized throughout the entire course of prenatal cortical neurogenesis. The small neurons and terminals from afferent systems of lower cortical strata, which are incorporated into layer I late in cortical neurogenesis, represent its non-essential components. The specific afferents of layer I are the first corticipetal fibers to arrive at the developing telencephalic vesicle marking the beginning of cortical neurogenesis. These primitive fibers extend throughout the surface of the cerebral vesicle establishing an external white matter. They are considered to be the stimulus for the development and maturation of the Cajal-Retzius neurons. Together they form a primitive cortical organization, the primordial plexiform layer, which precedes the appearance of the cortical plate and is considered to be common to and shared by amphibians, reptiles and mammals including man. Layer I evolves from this primordial cortical lamination. The Cajal-Retzius neurons are all characterized by a single descending axonic process which becomes a long horizontal (tangential) fiber in the lower half of layer I. Although the body and main dendrites of these neurons are only found at strategic and old cortical regions (e.g. the motor, acoustic and visual areas) their long horizontal axons extend, anteroposteriorly, throughout the entire surface of the cerebral cortex and establish synaptic connections with the apical dendrites of all pyramidal neurons regardless of location, cortical depth or functional role.In the course of cortical development, all developing pyramidal neurons ascend through the cortical plate in order to establish primary synaptic contacts with layer I. Only then, do they become ready to be displaced downward by the arrival of the next set of migrating neuroblasts. All pyramidal neurons of the cerebral cortex are actually suspended from layer I anchored to it by their apical dendritic bouquets. The need for all pyramidal neurons to reach and establish original synaptic connections with layer I could explain the remarkable inside-out formation of the cortical plate. This fact could also explain the characteristic shape of these neurons, as well as their abundance, structural uniformity and universal radial orientation to layer I. The functional role of layer I seems to be the spreading of the same kind of primitive information to all pyramidal neurons of the cerebral cortex whether they be motor, sensory, acoustic, visual or associational in nature, or whether they be large or small.The observations presented in this study further corroborate the concept of the dual origin of the mammalian cerebral cortex. The study emphasizes the important role played by layer I in the overall organization of the cerebral cortex. It proposes that in the course of cortical neurogenesis all future pyramidal neurons are attracted to layer I where they establish original synaptic connections and all receive from it the same kind of primitive information needed for their maturation. There seems to be no obvious reason to believe that the original synaptic contacts established between all pyramidal neurons and layer I disappear in the course of cortical neurogenesis. On the contrary, the progressive growth of the apical dendritic bouquets within layer I seems to indicate that they actually expand.This work has been supported by The National Institute of Child Health and Human Development (Grant #09274) NIH. U.S.A.     

Co-occurrence of chromosome 22q11.2 microdeletion and trisomy 21 mosaicism

This report describes a patient who had some phenotypic features of Down syndrome (DS) as well as severe conotruncal cardiac anomalies, including pulmonary atresia with ventricular septal defect (tetralogy of Fallot with pulmonary atresia), confluent pulmonary arteries, a large left-sided ductus arteriosus, left aortic arch, aberrant right subclavian artery, and secundum atrial septal defect. Cytogenetic and fluorescence in situ hybridization (FISH) analysis was carried out on peripheral blood lymphocytes and skin fibroblasts using probes specific for the chromosomal loci 21q22.13 to 21q22.2 and locus 22q11.2. This revealed 47,XX+21/46,XX mosaicism at a rate of 15:85 and the micro-deletion 22q11.2 (del22q11.2). Some patients'congenital cardiac anomalies are atypical for the type of mosaicism or aneuploidy. The case suggests that association of del22q11.2 should be considered in patients with chromosomal mosaicism or aneuploidy who also have particular conotruncal cardiac defects.     

A complex chromosome rearrangement resulting in trisomy 15q22→qter

A black infant with malformations was found to have trisomy 15q22→qter. The mother had a complex chromosomal rearrangement involving three chromosomes (5, 13, and 15). A comparison with previously published cases of trisomy for distal 15q suggests a pattern of clinical findings including retardation in growth and development, microcephaly, asymmetrical facies, prominent occiput, antimongoloid slant of the palpebral fissures, micrognathia, prominent nose, and congenital heart disease.