Features of trisomy 18 and 18p-syndromes in an infant with 46, XY, i(18q)

An isochromosome for the long arm of chromosome number 18 - 46,XY,i(18q) - was found in an infant who had features of both trisomy 18 and 18p- syndromes. Findings compatible with trisomy 18 included postmature delivery, prominent occiput, severe congenital heart disease, overlapping fingers, and rocker-bottom feet. Those of 18p- syndrome, which frequently resembles Turner syndrome, were downward obliquity to the palpebral fissures, short, webbed neck, low posterior hairline, and widely-spaced nipples. The infant died of heart failure at 3.5 months of age. Parental karyotypes were normal.     

Clinical delineation of a patient with trisomy 12q23q24

Trisomies of 12q23q24 have been described rarely in literature. Only a few case-reports have been published so far almost exclusively reporting on neonates or young infants. We present a 16-year-old patient with a trisomy of 12q23.3q24.3. Full phenotypic evaluation at this age comprised: severe growth retardation, developmental delay, intellectual disability and characteristic facial dysmorphisms. Initially, in the proband an insertion was cytogenetically mapped at chromosome 16: der(16)dir ins(16; 12)(q12.1; q24.11q24.31). The mother appeared carrier of a balanced insertion. Subsequent SNP-array analysis in the proband revealed a 16.3 Mb gain of 12q23.3 → 12q24.31. The clinical and molecular findings in this patient are compared with previous literature on cases with overlapping isolated 12q trisomies. The common phenotype observed consists of severe growth retardation, intellectual disability and characteristic facial features with hypertelorism, flat nasal bridge, down-turned mouth and poorly lobulated/low set ears. In addition, pediatric follow up into adolescence showed feeding difficulties requiring gastric tube feeding, recurrent otitis media, progressive contractures of joints and genito-renal problems, speech, communication and behavioral problems. These symptoms should be taken into account in the care and management of children with this condition.     

Isolated skeletal malformations in a child with a small mosaic ring microduplication of 18 p11.21q11.2: genotype-phenotype correlations

We describe a developmentally normal Amish child who has a karyotype with 47 chromosomes, including a supernumerary ring-shaped chromosome 18 in each metaphase studied. The only phenotypic findings in the patient were hemivertebrae and rib anomalies. Further analysis of interphase cells revealed an additional, less frequent mosaic, apparently normal cell population. Genes in the triplicated region that possibly are contributing to her skeletal phenotype include GATA6, MC2R, MC5R, RBBP8, ESCO1, and ROCK1, among others. By studying such patients with abnormal genetic dosage, genotype-phenotype correlations can be used to refine gene function.     

自贡地区630例智力低下、发育异常患者的细胞遗传学分析

目的通过对智力低下、发育异常患者进行细胞染色体核型分析,探讨智力低下、发育异常与染色体异常的关系。方法对630例智力低下、发育异常患者外周血进行淋巴细胞培养,制备染色体进行G显带,分析其染色体核型。结果630例智力低下、发育异常患者中染色体异常者219例,栓出率为34．8％,包括染色体数目异常、嵌合体、易位、倒位、及染色体多态性等多种改变,分别占20．5％、5．9％、4．1％、3．3％及1．0％,其中21-三体综合征核型最多见,共138例,占异常核型的63．O％,包括标准型、易位型及嵌合体型,分别占21-三体核型中的74．6％、15．2％及10．1％。结论染色体异常与智力低下、发育异常密切相关,应引起高度重视,对高危人群进行染色体检查,对临床诊断、治疗及指导优生优育具有重要意义。     

Prenatal detection of trisomy 18 caused by isochromosome 18p and 18q formation

We report on the prenatal detection and further genetic studies in a case of trisomy 18 caused by isochromosome 18p [i(18p)] and 18q [i(18q)] formation. The diagnosis was made by standard cytogenetic techniques in amniotic fluid cells and confirmed by fluorescence in situ hybridization. The formation of the isochromosomes cannot be explained by a single model; centromere misdivision and meiosis II nondisjunction without recombination or mitotic misdivision are the most likely mechanisms of formation as indicated by DNA analysis. Am. J. Med. Genet. 86:151–155, 1999. © 1999 Wiley-Liss, Inc.     

Trisomy (18q) and tetrasomy (18p) resulting from isochromosome formation

In this paper we report two clinically recognizable chromosomal syndromes, both resulting from isochromosome 18 formation, i.e. trisomy 18q and tetrasomy 18p. The possible mechanisms of the isochromosome formation are discussed and the literature on subject is reviewed.     

Trisomy 18 and 18p- features in a case of isochromosome 18q [46,XY,i(18q)]: prenatal diagnosis and autopsy report

This paper reports the prenatal diagnosis and autopsy findings of a case of true isochromosome 18q [46,XY,i(18q)] with severe cephalic malformations. Comparison is made with other cases of i(18q).     

1680例智力低下儿童的遗传咨询研究

1991年10月至1997年6月通过遗传咨询观察了智力低下（MR）儿童1680例,其中男性占53．3％,女性占46．7％;伴癫痫者占11．2％,伴脑瘫者占21％,第一胎占82．6％,轻度MR占73．8％,中度MR占22．9％,重度MR占3．3％,染色体核型异常检出率为14．6％．其中常染色体异常占73．1％,性染色体异常占26．9％,在病因探讨中,属于出生前因素占41．2％．出生时因素占26．5％,出生后因素占2．7％,原因不明占29．6％。     

Mild mental retardation in a child with a de novo interstitial deletion of 15q21.2q22.1: a comparison with previously described cases

We report on a child with mild mental retardation, hypotelorism, blepharophimosis, face slight asymmetry and partial hypoplasia of corpus callosum, with an interstitial deletion of a chromosome 15. The deletion was molecularly characterized by array-CGH and FISH techniques. This rearrangement has a 7.18 Mb extension and maps to 15q21.2q22.1. To date, there have been only six individuals reported with a deletion of 15q21; in three cases, the rearrangement was characterized by molecular cytogenetic techniques. After a comparison with these three cases, it appeared that the deletion we found is one of the smallest and it overlaps the distal portion of the ones taken into account. Finally, we tried to delineate the genotype–phenotype correlation in patients with a deletion of 15q21.     

Low-level complex mosaic with multiple cell lines affecting the 18q21.31q21.32 region in a patient with de novo 18q terminal deletion

We describe a 5-year-old girl who was diagnosed at birth with 18q de novo homogeneous deletion at G-banding karyotype. Her clinical condition, characterized by hypotonia, psychomotor retardation, short stature, deafness secondary to bilateral atresia of the external auditory canals, was in agreement with the 18q deletion syndrome though presence of coloboma of a single eye only suggested a mosaic condition as an unusual sign. By combining multiple technologies including array-CGH, FISH, and WGS, we found that the terminal deletion 18q21.32q23 (21 Mb) was in segmental mosaicism of the proximal region 18q21.31q21.32 (2.7 Mb), which showed a variable number of copies: one, two, or three, in 7, 41 and 55% of the cells respectively. Breakpoint junction analysis demonstrated the presence of an inv-dup del (18q) with a disomic segment of 4.7 kb between the inverted and non-inverted copies of the duplicated region 18q21.31q21.32. From these results, we propose that all three types of abnormal chr18 (the inv-dup del and the two 18q terminal deletions of different sizes) arisen from breaks in a dicentric mirror chromosome 18q, either in more than one embryo cell or from subsequent breaking-fusion-bridge cycles. The duplication region was with identical polymorphisms as in all non-recurrent inv-dup del rearrangements though, in contrast with most of them, the 18q abnormality was of maternal origin. Taking into account that distal 18q deletions are not rarely associated with inv-dup del(18q) cell lines, and that the non-disjunction of chromosome 18 takes place especially at maternal meiosis II rather than meiosis I, multiple rescue events starting from trisomic zygotes could be considered alternative to the postmitotic ones. From the clinical point of view, our case, as well as those of del(18q) in mosaic with the dic(18q), shows that the final phenotype is the sum of the different cell lines that acted on embryonic development with signs typical of both the 18q deletion syndrome and trisomy 18. Asymmetrical malformations, such as coloboma of the iris only in the right eye, confirm the underlying mosaicism regardless of whether it is still detectable in the blood.     

Recognizable behavioral and somatic phenotype in patients with proximal interstitial 18q deletion: Report on a new affected child and follow-up on the original reported familial cases

We describe a moderately retarded boy with a chromosome 18 deletion involving the regions q11.2q12.2. His phenotype is similar to that of other reported cases of proximal interstitial deletions involving 18q. We also provide follow-up information on the first 4 cases of proximal interstitial deletion of 18q from a family with a complex chromosome rearrangement originally reported in 1974. © 1992 Wiley-Liss, Inc.     

Translocation 46XY, t (17;18) (q25;q21) in a mentally retarded boy with progressive eye abnormalities

A 10-year-old boy with reciprocal translocation between chromosomes 17 and 18- 46XY,t (17;18) (q25; q21), appeared cytogenetically balanced. The patient was a healthy, thriving boy whose main abnormal feature was moderate mental retardation. However, abnormal ocular signs were present, including macular "fibrosis", optic disc abnormalities with a traction retinal detachment, tapeto-retinal degeneration, and tilting of the disc to the nasal side. These changes are consistent with the ocular changes previously described in the 18q- syndrome, suggesting that there has been a minimal deletion of chromosome material at the 18q21 breakpoint. The case also demonstrates that the ocular changes of the 18- syndrome may be progressive.     

Cytogenetic molecular delineation of a terminal 18q deletion suggesting neo-telomere formation

Deletion of the long arm of chromosome 18 is one of the most common segmental aneusomies compatible with life and usually involves a deletion of the terminal chromosomal region. However, the mechanisms implicated in the stabilization of terminal deletions are not well understood. In this study, we analyzed a girl with moderate mental retardation who had a cytogenetically visible terminal 18q deletion. In order to characterize the breakpoint in the terminal 18q region, we used fluorescence In situ hybridization (FISH) with bacterial artificial chromosomes (BACs) and pan-telomeric probes and also the array technique based on comparative genomic hybridization (array-CGH). FISH with pan-telomeric probes revealed no signal in the terminal region of the deleted chromosome, indicating the absence of normal telomere repeat (TTAGGG)n sequences in 18q. We suggest that neo-telomere formation by chromosome healing was involved in the repair and stabilization of this terminal deletion.     

Azoospermia in a man with a constitutional ring 22 chromosome

A mosaic ring chromosome 22 (mos 46,XY,r(22)[93]/45,XY,-22[7]) was found in an euploid azoospermic otherwise phenotypically normal individual. Testicular cytological analysis showed hypospermatogenesis with a complete spermatogonial arrest. The majority of subjects with constitutional r(22) are dysmorphic and mentally retarded due to deletion of a sizable segment of the chromosome 22q. Only a few cases of r(22) chromosome are known in which deletion of the very distal telomeric regions is associated with unremarkable phenotype and fertility, both in males and females. The present patient is the first example of male infertility associated with this cytogenetic anomaly. It is likely that infertility arose from a mechanical block of meiosis, resulting from pairing failure of chromosomes 22, similarly to azoospermia occurring in few known males with r(21) chromosomes.     

Chromosome 18q paracentric inversion in a family with mental retardation and hearing loss

We report on a mother and child with a paracentric inversion of the long arm of chromosome 18: 46,XX,inv(18)(q21.1q23). The child had findings in common with those seen in 18q- syndrome including: microcephaly, epicanthal folds, midface hypoplasia, and abnormally modeled ears, dermatoglyphic whorls on fingertips, clubfeet, hearing loss, and developmental delay. The mother and several maternal relatives had mild mental retardation and hearing loss. Magnetic resonance imaging of the child's brain showed abnormal myelination. Molecular studies including PCR-based markers for the MBP locus and fluorescent in situ hybridization with a P1 genomic clone on mother and child demonstrated only one copy of the MBP locus (18q23) with the deletion extending beyond the MBP locus. Therefore, the deletion in the MBP region may account for the abnormal myelination seen in the patient. The other clinical findings, including mental retardation and hearing loss in this family, may reflect disruption of distal or proximal genes within the deleted MBP region or at the more proximal breakpoint 18q21.1, and may represent a contiguous gene syndrome. Further study of this family may help define those genes functioning in the MBP region that contribute to the phenotype of 18q- syndrome. Am. J. Med. Genet. 76:372–378, 1998. © 1998 Wiley-Liss, Inc.     

2q24-q31 deletion: report of a case and review of the literature

We report a patient with a de novo interstitial deletion of the long arm of chromosome 2 involving bands 2q24.3-q31.1. The patient shows postnatal growth retardation, microcephaly, ptosis, down-slanting palpebral fissures, long eyelashes and micrognathia. Halluces are long, broad and medially deviated, while the other toes are laterally deviated and remarkably short with hypoplastic phalanges. She also showed developmental delay, seizures, lack of eye contact, stereotypic and repetitive hand movements and sleep disturbances with breath holding. Prenatal and three independent postnatal karyotypes were normal. Array-CGH analysis allowed us to identify and characterize a "de novo" 2q interstitial deletion of about 10.4Mb, involving segment between cytogenetic bands 2q24.3 and 2q31.1. The deletion was confirmed by quantitative PCR. About 30 children with 2q interstitial deletion have been reported. The deletion described here is overlapping with 15 of these cases. We have attempted to compare the clinical features of our patient with 15 overlapping cases. The emerging phenotypes include low birth weight, postnatal growth retardation, mental retardation and developmental delay, microcephaly, and peculiar facial dysmorphisms. Peculiar long and broad halluces with an increased distance between the first and the second toe are ("sandal gap" sign) present in most of the described patients. The gene content analysis of the deleted region revealed the presence of some genes that may be indicated as good candidates in generating both neurological and dysmorphic phenotype in the patient. In particular, a cluster of SCNA genes is located within the deleted region and it is known that loss of function mutations in SCNA1 gene cause a severe form of epilepsy.     

Case report of de novo dup(18p)/del(18q) and r(18) mosaicism

This is a report of a 27-year-old woman with an unusual de novo chromosomal abnormality. Mosaicism was identified in peripheral blood cells examined by standard G-bands by trypsin using Giemsa (GTG) analysis and fluorescence in situ hybridization (FISH) analysis with chromosome-18 region-specific probes, 46,XX,del(18)(pter → q21.33:)[41], 46,XX,r(18)(::p11.21 → q21.33::)[8], and 46,XX,der(18)(pter → q21.33::p11.21 → pter)[1]. On the other hand, the karyotype of periodontal ligament fibroblasts was nonmosaic, 46,XX, der(18)(pter → q21.33::p11.21 → pter)[50]. All cell lines appeared to be missing a portion of 18q (q21.33 → qter). The pattern of the dup(18p)/del(18q) in the rod configuration raises the possibility of an inversion in chromosome 18 in one of the parents. However, no chromosomal anomaly was detected in either parent. The most probable explanation is that de novo rod and ring configurations arose simultaneously from an intrachromosomal exchange. The unique phenotype of this patient, which included primary hypothyroidism and primary hypogonadism, is discussed in relation to her karyotype.     

一例22号环状染色体合并22ql3微缺失综合征患儿的临床及遗传学分析

目的探讨1例语言发育滞后患儿的遗传学病因。方法对患儿进行外周血染色体G显带分析以及单核昔酸多态性微阵列芯片(single nucleotide polymorphism microarray,SNP array)检测。结果患儿染色体核型为46,XY,r(22)(pll.2ql3),SNP array检测在22ql3区发现一处1.67 Mb的缺失,具体为arr[Hgl9]22ql3.33(49531302〜51197766)X1O结论患儿同时携带22号环状染色体以及22ql3微缺失,为明确其病因和遗传咨询提供了重要的线索。     

Congenital anomalies and anthropometry of 42 individuals with deletions of chromosome 18q

Deletions of chromosome 18q are among the most common segmental aneusomies compatible with life. The estimated frequency is approximately 1/40,000 live births [Cody JD, Pierce JF, Brkanac Z, Plaetke R, Ghidoni PD, Kaye CI, Leach RJ. 1997. Am. J. Med. Genet. 69:280–286]. Most deletions are terminal encompassing as much as 36 Mb, but interstitial deletions have also been reported. We have evaluated 42 subjects with deletions of 18q at our institution. This is the largest number of individuals with this chromosome abnormality studied by one group of investigators. Here we report the physical findings in these individuals. We have compared our findings with those of previously reported cases and have found a significantly different incidence of several minor anomalies in our subjects. We also describe here several anomalies not previously reported in individuals with deletions of 18q, including short frenulum, short palpebral fissures, disproportionate short stature, overlap of second and third toes, and a prominent abdominal venous pattern. Characteristics found in subjects were analyzed for correlation with cytogenetic breakpoints. Several traits were found to correlate with the extent of the deletion. Large deletions were associated with significantly decreased head circumference and ear length as well as the presence of proximally placed and/or anomalous thumbs. Individuals with the smallest deletions were more likely to have metatarsus adductus. Although relatively few genotype/phenotype correlations were apparent, these data demonstrate that correlations with breakpoint are possible. This implies that more correlations will become evident when the more precise molecularly based genotyping is completed. These correlations will identify critical regions on the chromosome in which genes responsible for specific abnormal phenotypes are located. Am. J. Med. Genet. 85:455–462, 1999. © 1999 Wiley-Liss, Inc.