Free proximal trisomy 21 without the Down syndrome

Analysis of partial duplication of chromosome 21 suggests that band 21q22 contains determinants for the Down syndrome. We report two cases of free proximal trisomy 21 without manifestations of the Down syndrome. Phenotypic anomalies included marked microcephaly, short stature, hypoplastic nails, and mental retardation/developmental delay. Our cases are consistent with the assignment of band 21q22 as the causal duplicated segment in the Down syndrome.     

Familial t (4;21)(q2.4;q2.2) leading to unbalanced offspring with partial duplication of 4q and of 21q without manifestations of the Down syndrome

We report on an infant with a malformation syndrome who had a combination of partial duplication of 4q and 21q as the result of a maternal unbalanced translocation. She has duplication of the proximal portion of chromosome 21, without manifestation of the Down syndrome.     

Tetrasomy 21 pter→q22.1 and Down syndrome: Molecular definition of the region

Down syndrome is usually caused by complete trisomy 21. Rarely, it is due to partial trisomy of the segment 21q22. We report on a 33-month-old girl with tetrasomy 21 pter → q22.1 resulting from an extra chromosome idic(21)(q22.1). She has craniofacial traits typical of Down syndrome, including brachycephaly, third fontanel, upward slanting palpebral fissures, round face, and protruding tongue. Speech development is quite delayed whereas motor development is only mildly retarded. The molecular content of the extra isodicentric chromosome was defined by molecular genetic investigations using 13 single copy probes unique to chromosome 21, and SOD1 expression studies. The child was found to have 4 copies of the region defined by D21S16 (21cen) through D21S93 on 21q22.1 and two copies of the remaining region defined by SOD1 → D21S55 → D21S123. In view of the recent assignment of Down syndrome facial characters to the 21q22 region, defined in part by D21S55, it is significant that this child shows a subset of Down syndrome facial manifestations, without duplication of this region. These results suggest that genes contributing to the facial and some of the hand manifestations of Down syndrome also exist in the chromosomal region proximal to D21S55 in band 21q22.1. © 1994 Wiley-Liss, Inc.     

Recombinant Down syndrome: a case report and literature review

We report a case of a child with features of Down syndrome (DS) but with an atypical karyotype. Initial chromosome analysis was 46,XX,dup(21q).ish 21(wcp21+). The father's chromosomes were normal. However, the mother was found to have mosaicism for a pericentric inversion of chromosome 21 (19/30 cells). The revised chromosome result of the child was 46,XX,rec(21)dup(21q)inv(21)(p12q21.1)mat. A literature review of similar cases (hereafter referred to as rec dup(21q)) was conducted to aid counselling about recurrence risks and the prognosis for this child. All previous reports of rec dup(21q) were secondary to a maternal pericentric inversion. Male carriers did not seem to be at risk of having offspring with the rec dup(21q), although the number of male carriers was limited. In those with rec dup(21q), the risk of congenital heart disease was similar to that of trisomy 21. In reported cases, the facial appearance was suggestive of Down syndrome but perhaps less striking. Although the data are limited, there is an indication the developmental disabilities and short stature are milder in those with rec dup(21q) compared to trisomy 21. These observations promote the concept that the region of chromosome 21 proximal to the duplication contains genetic information contributing to the expression of some features of Down syndrome.     

Lumpers,splitters, and FGFRs

We report on a girl with a large interstitial deletion of the long arm of chromosome 21 and with mild mental retardation, congenital hypothyroidism, and hyperopia. The deletion [del(21)(q11.1–q22.1)] extends molecularly from marker D21S215 to D21S213. The distal breakpoint is not clearly defined but is situated between markers D21S213 and IFNAR. This patient has the largest deletion of chromosome 21 known without having severe mental retardation or malformations. The deletion does not involve the “Down syndrome chromosome” region, the region of chromosome 21 which in trisomy causes most of the manifestations of Down syndrome. Apparently, the proximal part of the long arm of chromosome 21 does not include genes that are responsible for severe clinical effects in the event of either deletion or duplication, since several reported patients with either trisomy or deletion of this region have mild phenotypic abnormalities. Congenital hypothyroidism is much more common in Down syndrome than in the average population. Thus, the congenital hypothyroidism of the present patient might indicate that there is one or several genes on the proximal part of chromosome 21, which might be of importance for the thyroid function. © 1996 Wiley-Liss, Inc.     

Del(X) (q26) in a phenotypically normal woman and her daughter who also has trisomy 21

We present a phenotypically normal woman with del(X)(q26) with no evidence of mosaicism, who had two pregnancies resulting in two live-born infants. Her first child had trisomy 21 Down syndrome and the del(X)(q26). To our knowledge, this woman is the first known case of presumably nonmosaic del(Xq) producing live-born infants. This finding can be explained on the basis of persistence into adulthood of germ cells in ovaries of the rare del(Xq) individuals. The normal phenotype in this woman supports the hypothesis that the absence of genes of middle Xq segment.(q13 → q26) is responsible for the somatic manifestations of the Ullrich-Turner syndrome. Our finding suggests that prenatal diagnosis should be offered not only to pregnant women with numerical X chromosome abnormalities, as suggested previously, but also to those with structural X chromosome abnormalities, because of the possibility of chromosome aberrations in the offspring of such women.     

Mental retardation, congenital heart malformation, and myelodysplasia in a patient with a complex chromosomal rearrangement involving the critical region 21q22

The region 21q22 is considered crucial for the pathogenesis of both Down syndrome (DS) and the partial monosomy 21q syndrome. Haploinsufficiency of the RUNX-1 gene, mapping at 21q22 is responsible for a platelet disorder and causes predisposition to myelodysplastic syndrome (MDS). We describe a 3-year-old girl with mental retardation, congenital heart malformation, and subtle dysmorphic facial features. The patient developed thrombocytopenia when she was 2 years old. Bone marrow smear led to the diagnosis of myelodysplasia. Prenatal karyotyping had shown chromosome 21 pericentric inversion. Postnatally the array-CGH revealed duplication at bands 21q11.2-21q21.1 and a simultaneous deletion involving the region 21q22.13-21q22.3. RUNX-1 mRNA levels analyzed in patient's skin fibroblasts were reduced. In this child the monosomy of the region 21q22 likely had the main role in determining the phenotype. Although the RUNX-1 gene is localized outside the deleted region, we speculate that RUNX-1 reduced expression, is probably due to the deletion of regulatory factors and caused the hematologic disorder in the patient. The present report underlines also the importance of array-CGH in characterizing patients with a complex phenotype.     

Antenatal manifestations of Smith-Lemli-Opitz (RSH) syndrome: a retrospective survey of 30 cases

We report on a case of an interstitial duplication of 11q in a patient with developmental delay and in his moderately delayed mother. Partial trisomy 11q is well documented in the literature with most cases involving the distal region of the long arm of chromosome 11. In almost all cases, this trisomy is associated with monosomy of the second chromosome involved in the parental translocation. The most common, partial 11q and 22q trisomy syndrome, is observed in offspring of t(11;22)(q23;q11.2) carriers from a 3:1 tertiary trisomic malsegregation. We found only two previous reports of pure partial trisomy 11q in the literature. Comparison of the clinical findings of our patient and another single published report of duplication in the same segment of chromosome 11 suggests that the duplication of this region manifests mild phenotypic abnormalities.     

Mosaicism del(22)(q11.2q11.2)/dup(22)(q11.2q11.2) in a patient with features of 22q11.2 deletion syndrome

The chromosome 22q11 region is prone to rearrangements, including deletions and duplications, due to the presence of multiple low copy repeats (LCRs). DiGeorge/velo-cardio-facial syndrome is the most common microdeletion syndrome with more than 90% of patients having a common 3-Mb deletion of 22q11.2 secondary to non-homologous recombination of flanking LCRs. Meiotic reciprocal events caused by LCR-mediated rearrangement should theoretically lead to an equal number of deletions and duplications. Duplications of this region, however, have been infrequently reported and vary in size from 3 to 6 Mb. This discrepancy may be explained by the difficulty in detecting the duplication and the variable, sometimes quite mild phenotype. This newly described 22q duplication syndrome is characterized by palatal defects, cognitive deficits, minor ear anomalies, and characteristic facial features. We report on a male with truncus arteriosus and an interrupted aortic arch, immunodeficiency, and hypocalcemia. The patient is mosaic for two abnormal cell lines: a deletion [del(22)(q11.2q11.2)] found in 11 cells and a duplication [dup(22)(q11.2q11.2)] found in 9 cells. Molecular cytogenetic analysis in our patient revealed a 1.5 Mb deletion/duplication, the first duplication reported of this size. Deletion/duplication mosaicism, which is rare, has been reported in a number of cases involving many different chromosome segments. We present the clinical phenotype of our patient in comparison to the phenotypes seen in patients with the 22q11.2 deletion or duplication alone. We propose that this rearrangement arose by a mitotic event involving unequal crossover in an early mitotic division facilitated by LCRs.     

Patient with terminal duplication 3q and terminal deletion 5q: comparison with the 3q duplication syndrome and distal 5q deletion syndrome

Partial duplication of chromosome 3q is a well-described condition of multiple congenital anomalies and developmental delay that resembles the Brachmann-de Lange syndrome. Similarly, an emerging phenotype of a distal 5q deletion syndrome has recently been described. The combination of both chromosome abnormalities has not been previously described. We report on a child with both a de novo duplication of distal 3q (q27 --> qter) and terminal deletion of 5q (q35.2 --> qter). The patient had facial anomalies, hypoplastic toenails, lymphedema of the dorsum of the feet, type I Chiari malformation, a seizure disorder, and moderate developmental delays. The phenotype is compared and contrasted to the few reports of patients with similar terminal 3q duplications and 5q deletions. Our patient did not have the characteristic phenotype of the 3q duplication syndrome, suggesting that the chromosome region responsible for this phenotype is more proximal than the terminal 3q27 region. In addition, comparison with three other reported cases of terminal 5q35 deletions suggests a possible association of terminal 5q deletions with central nervous system (CNS) structural abnormalities.     

Mirror-symmetric duplicated chromosome 21q with minor proximal deletion, and with neocentromere in a child without the classical Down syndrome phenotype

We report on a mentally retarded child with multiple minor anomalies and an unusually rearranged chromosome 21. This der(21) chromosome has a deletion of 21p and of proximal 21q, whereas the main portion of 21q is duplicated leading to a mirror-symmetric appearance with the mirror axis at the breakpoint. The centromere is only characterized by a secondary constriction (with a centromeric index of a G chromosome) at an unexpected distal position, but fluorescence in situ hybridization (FISH) with either chromosome specific or with all human centromeres alpha satellite DNA shows no cross hybridization. Thus, the marker chromosome represents a further example of an "analphoid marker with neocentromere." Molecular analysis using polymorphic markers on chromosome 21 verified a very small monosomic segment of the proximal long arm of chromosome 21, and additionally trisomy of the remaining distal segment. Although trisomic for almost the entire 21q arm, our patient shows no classical Down syndrome phenotype, but only a few minor anomalies found in trisomy 21 and in monosomy of proximal 21q, respectively.     

Two cases of partial trisomy 21 (pter-q22.1) without the major features of Down syndrome

We report two cases of partial trisomy 21 with clinical features distinct from Down syndrome (DS). These patients presented with moderate mental retardation and short stature, but the typical facial appearance of DS was not observed. Each patient had a similarly sized extra chromosome 21. We performed FISH analysis to examine whether deletions of reported approximately 5 Mb DS critical region (DSCR) might be associated with unusual clinical features in these cases. The results showed that each of their extra chromosomes 21 contained a distal part of chromosome 3p or 14q at the telomeric region of chromosome 21q. The translocation breakpoint of 21q for each patient was located on the centromeric side of DSCR (DSCR was deleted) and the sizes of partial trisomy 21 in respective patients are approximately 34.5 (21pter-q22.12) and approximately 33.0 Mb (21pter-q22.11). In one patient, the additional region of the short arm of chromosome 3 was 3pter-p26.1 from maternal origin, measuring approximately 9 Mb in size. The second patient had an extra 14q32.1-qter of maternal origin, measuring approximately 14 Mb in size. These are one of the shortest partial distal trisomy among reported cases. Taken together, two patients with partial trisomy 21 lack all of DSCR on 21q22, and their distinct clinical features are likely caused by the genes located at 21pter-q22.1 and the distal part of chromosome 3p or 14q.     

Duplication 6q syndrome.

Duplication (partial trisomy) of the long arm of chromosome 6 has been described in 5 children [Robertson et al, 1975, Chen et al, 1976, Clark, 1977]. We wish to report here an additional case due to a familial translocation in which the proband's karyotype is 46,XX,der(3),rcp(3;6)(p25;q21)mat. The phenotypes of the 6 children with duplication 6q are strikingly similar. Each child has duplication involving approximately the distal 1/3 to 1/2 of the long arm of chromosome 6. Distinctive features present in all 6 children include microcephaly, acrocephaly, prominent forehead, flat facial profile, depressed nasal bridge, flat malar areas, "carp" mouth, micrognathia and mental retardation. The phenotype of the duplication 6q syndrome is distinctive enough to be clinically recognizable.     

Pure familial 6q21q22.1 duplication in two generations

Familial transmissions of unbalanced chromosomal abnormalities are rare. We report here the first case of a maternally inherited pure partial duplication of the long arm of chromosome 6 [46,XX,dup(6)(q21q22.1)mat]. The proband was referred for karyotyping as she presented intrauterine growth retardation (IUGR), moderate mental retardation and facial dysmorphism. Molecular cytogenetics analysis with various BACs showed a duplication of 5-10 Mb between 6q21 and 6q22.1. The proband's mother was found to have the same chromosome abnormality and a similar phenotype, but less severe dysmorphism. This variability in clinical findings between generations may have several causes, including attenuation with aging, imprinting or mosaicism. Only three other cases of pure partial 6q duplication similar to that of our case have been reported. The available information for all four cases was used to refine the karyotype-phenotype correlations for duplications of the 6q21q22 segment.     

Cryptic duplication of 21q in an individual with a clinical diagnosis of Down syndrome

We describe an adult male who was diagnosed with Down syndrome (DS) at 9 months of age, but had repeatedly normal karyotypes until recent mid‐resolution chromosome studies showed a possible duplication of 21q22.13 to 21q22.3. The abnormality was investigated using fluorescent in situ hybridization (FISH) studies. These showed hybridization of a whole chromosome paint probe (wcp21, Oncor Coatasome 21) to the entire length of both chromosome 21 homologues and one very large hybridization signal of a cosmid contig probe localized within bands 21q22.13‐21q22.2(LSI‐21, Vysis) on the ?dup(21q) homologue. CGH analysis identified a ratio of 1.5 for the segment of chromosome 21 involving band 21q22, indicating a gain of part, or all, of the terminal band of chromosome 21. The karyotype was thus defined as 46,XY,?dup(21) (q22.13q22.2).ish dup(21)(LSI‐21++,wcp21+). Common DS characteristics in our case and 12 previously reported cases with duplications involving chromosome 21 included mental retardation, fifth finger clinodactyly, open mouth and oblique eye fissures. Transverse palmar creases and congenital heart defects, seen in DS less than 40% of the time, were infrequent. Presence of these features did not appear to depend on the specific portion of chromosome 21 that was duplicated. A review of 18 additional clinical features showed no consistent phenotype–genotype correlations.     

Further delineation of the partial proximal trisomy 10q syndrome.

We report on a girl with a partial duplication of the proximal part of the long arm of chromosome 10, confirmed by chromosome painting. The phenotypic findings are compared to those found in six other published cases with the same karyotype. Recognition of a specific partial proximal trisomy 10q syndrome seems to be possible, consisting of mild to moderate developmental delay, postnatal growth retardation, microcephaly, prominent forehead, small and deep set eyes, epicanthus, upturned nose, bow shaped mouth, micrognathia, thick and flat helices of the ears, and long, slender limbs. Severe ocular malformations are possibly part of the syndrome. No major phenotypic differences were seen between patients with a duplication of segment 10q11-->10q22 and patients with a duplication of 10q21-->10q22.     

Down syndrome due to partial trisomy 21q

A patient is reported with a typical Down syndrome phenotype, caused by patrial trisomy of chromosome 21. Based on the present case and data from the literature, it is suggested that the Down phenotype is due to the trisomy of the distal portion of the band (q22) of chromosome 21.     

Duplication 8q12: confirmation of a novel recognizable phenotype with duane retraction syndrome and developmental delay

Duane retraction syndrome (DRS) is a rare congenital strabismus condition with genetic heterogeneity. DRS associated with intellectual disability or developmental delay is observed in several genetic diseases: syndromes such as Goldenhar or Wildervanck syndrome and chromosomal anomalies such as 12q12 deletion. We report on the case of a patient with DRS, developmental delay and particular facial features (horizontal and flared eyebrows, long and smooth philtrum, thin upper lip, full lower lip and full cheeks). We identified a duplication of the long arm of chromosome 8 (8q12) with SNP-array. This is the third case of a patient with common clinical features and 8q12 duplication described in the literature. The minimal critical region is 1.2 Mb and encompasses four genes: CA8, RAB2, RLBP1L1 and CHD7. To our knowledge, no information is available in the literature regarding pathological effects caused by to overexpression of these genes. However, loss of function of the CHD7 gene leads to CHARGE syndrome, suggesting a possible role of the overexpression of this gene in the phenotype observed in 8q12 duplication patients. We have observed that patients with 8q12 duplication share a common recognizable phenotype characterized by DRS, developmental delay and facial features. Such data combined to the literature strongly suggest that this entity may define a novel syndrome. We hypothesize that CHD7 duplication is responsible for a part of the features observed in 8q12.2 duplication.     

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.     

Mirror‐symmetric duplicated chromosome 21q with minor proximal deletion,and with neocentromere in a child without the classical Down syndrome phenotype

We report on a mentally retarded child with multiple minor anomalies and an unusually rearranged chromosome 21. This der(21) chromosome has a deletion of 21p and of proximal 21q, whereas the main portion of 21q is duplicated leading to a mirror‐symmetric appearance with the mirror axis at the breakpoint. The centromere is only characterized by a secondary constriction (with a centromeric index of a G chromosome) at an unexpected distal position, but fluorescence in situ hybridization (FISH) with either chromosome specific or with all human centromeres alpha satellite DNA shows no cross hybridization. Thus, the marker chromosome represents a further example of an “analphoid marker with neocentromere.” Molecular analysis using polymorphic markers on chromosome 21 verified a very small monosomic segment of the proximal long arm of chromosome 21, and additionally trisomy of the remaining distal segment. Although trisomic for almost the entire 21q arm, our patient shows no classical Down syndrome phenotype, but only a few minor anomalies found in trisomy 21 and in monosomy of proximal 21q, respectively. Am. J. Med. Genet. 91:116–122, 2000. © 2000 Wiley‐Liss, Inc.