Partial trisomy of chromosome 22 resulting from an interstitial duplication of 22q11.2 in a child with typical cat eye syndrome

Prenatal Diagnosis Using Chromosomal Microarray Analysis in High-Risk Pregnancies

Background: To assess the value of chromosomal microarray analysis (CMA) during the prenatal diagnosis of high-risk pregnancies. Methods: Between January 2016 and November 2021, we included 178 chorionic villi and 859 amniocentesis samples from consecutive cases at a multiple tertiary hospital. Each of these high-risk singleton pregnancies had at least one of the following indications: (1) advanced maternal age (AMA; ≥35 years; 546, 52.7%); (2) fetal structural abnormality on ultrasound (197, 19.0%); (3) high-risk first- or second-trimester Down syndrome screen (189, 18.2%), including increased nuchal translucency (≥3.5 mm; 90, 8.7%); or (4) previous pregnancy, child, or family history (105, 10.1%) affected by chromosomal abnormality or genetic disorder. Both G-banding karyotype analysis and CMA were performed. DNA was extracted directly and examined with oligonucleotide array-based comparative genomic hybridization. Results: Aneuploidies were detected by both G-banding karyotyping and CMA in 42/1037 (4.05%) cases. Among the 979 cases with normal karyotypes, 110 (10.6%) cases had copy number variants (CNVs) in CMA, including 30 (2.9%) cases with reported pathogenic and likely pathogenic CNVs ≥ 400 kb, 37 (3.6%) with nonreported VOUS, benign, or likely benign CNVs ≥ 400 kb, and 43 (4.1%) with nonreported CNVs < 400 kb. Of the 58 (5.6%) cases with aneuploidy rearrangements, 42 (4.1%) were diagnosed by both G-banding karyotyping and CMA; four inversions, six balanced translocations, and six low mosaic rates were not detected with CMA. Conclusions: CMA is an effective first step for the prenatal diagnosis of high-risk pregnancies with fetal structural anomalies found in ultrasonography or upon positive findings.

Müllerian Agenesis in Cat Eye Syndrome and 22q11 Chromosome Abnormalities: A Case Report and Literature Review

BACKGROUND

Although Müllerian agenesis is the second most common cause of primary amenorrhea the underlying etiology in most cases is unknown. Müllerian agenesis has been reported as a rare finding associated with chromosomal aberrations of the 22q11 chromosomal region including at least 1 individual with cat eye syndrome (CES) and 10 individuals with deletions or duplications of the 22q11.2 region. However, a potential link between 22q11 abnormalities and uterine malformations has been difficult to adequately ascertain because of the limited case reports in the literature.

CASE

We report a second case of Müllerian agenesis in a girl with CES. A 16-year-old girl presented with bilateral colobomata, primary amenorrhea, and absence of the uterus and upper vagina on pelvic magnetic resonance imaging. Microarray analysis showed tetrasomy of the pericentromeric region of chromosome 22 diagnostic of CES.

SUMMARY AND CONCLUSION

Müllerian aplasia/hypoplasia might represent a rare feature in CES and should be considered in the investigation of young girls with this syndrome. An increasing number of cases with 22q11 chromosome abnormalities and Müllerian agenesis further highlights the possibility of a gene within the 22q11 region that might mediate normal Müllerian development in girls.

22q11.2 microduplication syndrome with associated esophageal atresia/tracheo-esophageal fistula and vascular ring

This case report describes a patient with a 22q11.2 duplication. His features, which include VACTERL association with an esophageal atresia/tracheo‐esophageal fistula and a vascular ring, expand the previously described phenotype for this duplication.

Genetic Techniques in the Evaluation of Short Stature

Normal growth is a complex dynamic process dependent on the coordination of multiple factors including genetics, nutrition and hormones that are all working in balance. This chapter will review selected features of commonly utilized genetic techniques such as chromosomal analysis, microarray analysis, targeted gene screening and whole exome sequencing that are being used to identify genes influencing growth. As genetic technologies continue to improve and become more accessible many of these techniques will help to provide a better understanding of mechanisms underlying abnormal growth and will eventually lead to novel management approaches for abnormal growth.

Cytogenomic Aberrations in Congenital Cardiovascular Malformations

Congenital cardiovascular malformations are the most common birth defects, with a complex multifactorial etiology. Genetic factors play an important role, illuminated by numerous cytogenetically visible abnormalities, as well as submicroscopic genomic imbalances affecting critical genomic regions in the affected individuals. Study of rare families with Mendelian forms, as well as emerging next-generation sequencing technologies have uncovered a multitude of genes relevant for human congenital cardiac diseases. It is clear that the complex embryology of human cardiac development, with an orchestrated interplay of transcription factors, chromatin regulators, and signal transduction pathway molecules can be easily perturbed by genomic imbalances affecting dosage-sensitive regions. This review focuses on chromosomal abnormalities contributing to congenital heart diseases and underscores several genomic disorders linked to human cardiac malformations in the last few decades.

Severe psychomotor delay in a severe presentation of cat-eye syndrome

Cat-eye syndrome is a rare genetic syndrome of chromosomal origin. Individuals with cat-eye syndrome are characterized by the presence of preauricular pits and/or tags, anal atresia, and iris coloboma. Many reported cases also presented with variable congenital anomalies and intellectual disability. Most patients diagnosed with CES carry a small supernumerary bisatellited marker chromosome, resulting in partial tetrasomy of 22p-22q11.21. There are two types of small supernumerary marker chromosome, depending on the breakpoint site. In a very small proportion of cases, other cytogenetic anomalies are reportedly associated with the cat-eye syndrome phenotype. Here, we report a patient with cat-eye syndrome caused by a type 1 small supernumerary marker chromosome. The phenotype was atypical and included a severe developmental delay. The use of array comparative genomic hybridization ruled out the involvement of another chromosomal imbalance in the neurological phenotype. In the literature, only a few patients with cat-eye syndrome present with a severe developmental delay, and all of the latter carried an atypical partial trisomy 22 or an uncharacterized small supernumerary marker chromosome. Hence, this is the first report of a severe neurological phenotype in cat-eye syndrome with a typical type 1 small supernumerary marker chromosome. Our observation clearly complicates prognostic assessment, particularly when cat-eye syndrome is diagnosed prenatally.

Altered Tbx1 gene expression is associated with abnormal oesophageal development in the adriamycin mouse model of oesophageal atresia/tracheo-oesophageal fistula

INTRODUCTION

Oesophageal atresia/tracheo-oesophageal atresia (OA/TOF) frequently arises with associated anomalies and has been clinically linked with 22q11 deletion syndromes, a group of conditions due to Tbx1 gene mutation which include Di George syndrome. Tbx1 and Tbx2 genes modulate pharyngeal and cardiac development, but are also expressed in the developing foregut and are known to interact with key signalling pathways described in oesophageal formation including bone morphogenic proteins. The adriamycin mouse model (AMM) reliably displays OA/TOF-like foregut malformations providing a powerful system for investigating the disturbances in gene regulation and morphology involved in tracheo-oesophageal malformations. We hypothesised that foregut abnormalities observed in the AMM are associated with altered Tbx1 and Tbx2 gene expression.

METHODS

Time-mated CBA/Ca mice received intra-peritoneal injection of adriamycin (for treated) or saline (for controls) on embryonic days (E)7 and 8. Untreated Cd1 embryos were used to establish normal expression patterns. Embryos harvested on E9-E11 underwent whole-mount in situ hybridization with labelled RNA probes for Tbx1 and Tbx2. Optical projection tomography was used to visualise expression in whole embryos by 3D imaging.

RESULTS

Tbx1 expression was visualised in a highly specific pattern in the proximal oesophageal endoderm in normal and control embryos. In the AMM, extensive ectopic expression of Tbx1 was detected in the dorsal foregut and adjacent to the TOF. The focally restricted oesophageal expression pattern persisted in the AMM, but was posteriorly displaced in relation to the tracheal bifurcation. Tbx2 was widely expressed in the ventral foregut mesoderm of controls, lacking specific endoderm localisation. In the AMM, altered Tbx2 expression in the foregut was only seen in severely affected embryos.

CONCLUSION

Highly specific Tbx1 expression in the proximal oesophageal endoderm suggests that Tbx1 may be an important regulator of normal oesophageal development. Altered Tbx1 expression in dorsal foregut and adjacent to the TOF in the AMM suggests that Tbx1 gene disruption may contribute to the pathogenesis of tracheo-oesophageal malformations.

Coloboma and anorectal malformations: a rare association with important clinical implications

PURPOSE

In a patient with an anorectal malformation (ARM), the presence of a coloboma is commonly associated with other serious anomalies.

METHODS

Our database and the world literature were reviewed searching for associated defects in patients with ARM and coloboma.

RESULTS

Of 2,482 ARMs in our database, 11 had coloboma (0.4%): 2 were females. No specific associated type of ARM was identified. Six patients were developmentally delayed. Eight had a cardiac anomaly (3 had TAPVR, 2 VSD, 3 ASD), five required a cardiac operation. Five had a gastrointestinal anomaly (3 malrotation, 1 biliary and 1 duodenal atresia). Six had eye and seven had ear anomalies. Five had a genetic abnormality. In the literature, 71 patients with ARM and coloboma were found: 65 % were females. 24% died prematurely. 74% were developmentally delayed. 70% had a cardiac malformation (35% had TAPVR, 38% required an operation). 57% had gastrointestinal anomalies (31% malrotation, 31 % biliary atresia, 17% Hirschsprung disease). Eye and ear anomalies were present in 80 and 97% of patients, respectively. 81% had a genetic abnormality.

CONCLUSIONS

An ocular inspection in patients born with ARM is crucial. The finding of a coloboma should increase awareness to evaluate for a developmental, cardiologic or gastrointestinal anomaly.

Hemifacial microsomia in cat-eye syndrome: 22q11.1-q11.21 as candidate loci for facial symmetry

Cat-Eye syndrome (CES), (OMIM 115470) also known as chromosome 22 partial tetrasomy or inverted duplicated 22q11, was first reported by Haab [1879] based on the primary features of eye coloboma and anal atresia. However, >60% of the patients lack these primary features. Here, we present a 9-month-old female who at birth was noted to have multiple defects, including facial asymmetry with asymmetric retrognathia, bilateral mandibular hypoplasia, branchial cleft sinus, right-sided muscular torticollis, esotropia, and an atretic right ear canal with low-to-moderate sensorineural hearing loss, bilateral preauricular ear tag/pits, and two skin tags on her left cheek. There were no signs of any colobomas or anal atresia. Hemifacial microsomia (HFM) was suspected clinically. Chromosome studies and FISH identified an extra marker originated from 22q11 consistent with CES, and this was confirmed by aCGH. This report expands the phenotypic variability of CES and includes partial tetrasomy of 22q11.1-q11.21 in the differential diagnosis of HFM. In addition, our case as well as the previous association of 22q11.2 deletions and duplications with facial asymmetry and features of HFM, supports the hypothesis that this chromosome region harbors genes important in the regulation of body plan symmetry, and in particular facial harmony.

A de novo sSMC(22) Characterized by High-Resolution Arrays in a Girl with Cat-Eye Syndrome without Coloboma

Cat-eye syndrome (CES) results from trisomy or tetrasomy of proximal 22q originated by a small supernumerary marker chromosome (sSMC). Two critical regions for the major clinical features of CES (CESCRs) have been suggested; however, CES clinical presentation often does not correlate with the sSMC genetic content. We report here a CES girl without coloboma and carrier of a de novo type I sSMC(22) as determined by G- and C-banding, NOR staining and microarrays. This sSMC included 6 distal genes outside the original CESCR and led to a tetrasomy for 22q11.1-22q11.21. The patient's final karyotype was 47,XX,+psu dic(22)(q11.21).arr 22q11.1q11.21(15,250,000-17,035,860)×4 dn. The amplified region outside of CESCR included some genes that may be related to neurologic, heart and renal abnormalities. Conversely, even though the amplification included the CECR2 gene, a major candidate for eye features, there was no coloboma in the patient. The genetic delineation of the present sSMC further strengthens that the CES clinical presentation does not fit completely with the duplicated genetic content and that CES is actually a genomic disorder. Furthermore, since we observed no mosaicism, we believe that other mechanisms might be behind the variability of CES phenotypes as well, mainly those related with functional interactions among amplified genes.

An unusual case of Cat-Eye syndrome phenotype and extragonadal mature teratoma: review of the literature

BACKGROUND Cat-Eye syndrome (CES) with teratoma has not been previously reported. We present the clinical and molecular findings of a 9-month-old girl with features of CES and also a palpable midline neck mass proved to be an extragonadal mature teratoma, additionally characterized by array comparative genomic hybridization (aCGH). RESULTS High resolution oligonucleotide-based aCGH confirmed that the supernumerary marker chromosome (SMC) derived from chromosome 22, as was indicated by molecular cytogenetic analysis with fluorescence in situ hybridization (FISH). Additionally, aCGH clarified the size, breakpoints, and gene content of the duplication (dup 22q11.1q11.21; size:1.6 Mb; breakpoints: 15,438,946-17,041,773; hg18). The teratoma tissue was also tested with aCGH, in which the CES duplication was not found, but the analysis revealed three aberrations: del Xp22.3 (108,864-2788,689; 2.7 Mb hg18), dup Yp11.2 (6688,491-7340,982; 0.65 Mb, hg18), and dup Yq11.2q11.23 (12,570,853-27,177,133; 14.61 Mb, hg18). These results indicated 46 XY (male) karyotype of the teratoma tissue, making this the second report of mature extragonadal teratoma in a female neonate, probably deriving from an included dizygotic twin of opposite sex (fetus in fetu). CONCLUSIONS Our findings extend the phenotypic spectrum of CES syndrome, a disorder with clinical variability, pointing out specific dosage-sensitive genes that might contribute to specific phenotypic features.

A 600 kb triplication in the cat eye syndrome critical region causes anorectal, renal and preauricular anomalies in a three-generation family

Cat eye syndrome (CES) is caused by a gain of the proximal part of chromosome 22. Usually, a supernumerary marker chromosome is present, containing two extra copies of the chromosome 22q11.1q11.21 region. More sporadically, the gain is present intrachromosomally. The critical region for CES is currently estimated to be about 2.1 Mb and to contain at least 14 RefSeq genes. Gain of this region may cause ocular coloboma, preauricular, anorectal, urogenital and congenital heart malformations. We describe a family in which a 600 kb intrachromosomal triplication is present in at least three generations. The copy number alteration was detected using MLPA and further characterized with interphase and metaphase FISH and SNP-array. The amplified fragment is located in the distal part of the CES region. The family members show anal atresia and preauricular tags or pits, matching part of the phenotype of this syndrome. This finding suggests that amplification of the genes CECR2, SLC25A18 and ATP6V1E1, mapping within the critical region for CES, may be responsible for anorectal, renal and preauricular anomalies in patients with CES.

Structural basis for the growth factor activity of human adenosine deaminase ADA2

Two distinct adenosine deaminases, ADA1 and ADA2, are found in humans. ADA1 has an important role in lymphocyte function and inherited mutations in ADA1 result in severe combined immunodeficiency. The recently isolated ADA2 belongs to the novel family of adenosine deaminase growth factors (ADGFs), which play an important role in tissue development. The crystal structures of ADA2 and ADA2 bound to a transition state analogue presented here reveal the structural basis of the catalytic/signaling activity of ADGF/ADA2 proteins. In addition to the catalytic domain, the structures discovered two ADGF/ADA2-specific domains of novel folds that mediate the protein dimerization and binding to the cell surface receptors. This complex architecture is in sharp contrast with that of monomeric single domain ADA1. An extensive glycosylation and the presence of a conserved disulfide bond and a signal peptide in ADA2 strongly suggest that ADA2, in contrast to ADA1, is specifically designed to act in the extracellular environment. The comparison of catalytic sites of ADA2 and ADA1 demonstrates large differences in the arrangement of the substrate-binding pockets. These structural differences explain the substrate and inhibitor specificity of adenosine deaminases and provide the basis for a rational design of ADA2-targeting drugs to modulate the immune system responses in pathophysiological conditions.

Schmid-Fraccaro syndrome: severe neurologic features

Schmid-Fraccaro syndrome is a rare genetic disease, characterized by modifications of chromosome 22 (partial trisomy or tetrasomy), accompanied by eye abnormality (coloboma) and anal atresia. Clinical and phenotypic features are variable, and neurologic disturbance with delays of mental, psychologic, and motor development may be present. Its definitive diagnosis is based on karyotype. We report on a 17-year-old girl with Schmid-Fraccaro syndrome and severe cognitive deficits and motor deficits, who presented at our healthcare unit for a medical consultation. Her physical examination was remarkable for bilateral coloboma of the iris, hypertelorism, bilateral preauricular tags, scoliosis, and cardiac systolic murmur. After her birth, she was evaluated for anal atresia and congenital cardiac disease, which led to a genetic investigation and a diagnosis of Schmid-Fraccaro syndrome. Life expectancy in Schmid-Fraccaro syndrome depends on the number and variety of malformations, but in most cases the prognosis is favorable.

Two distinctive classic genetic syndromes, 22q11.2 deletion syndrome and Angelman syndrome, occurring within the same family

We document a sib pair born to a mother with a reciprocal translocation, t(15;22)(q13;q11.2): the daughter had the Angelman syndrome phenotype associated with a maternally derived 15q deletion, and the son had a phenotype associated with a 22q deletion. Adjacent two-type segregation during gametogenesis in the mother can account for the unbalanced karyotypes of the siblings. From a tetravalent chromatid formed by normal chromosome 15, derivative chromosome 15, normal chromosome 22, and derivative chromosome 22, the daughter inherited chromosome 22 and derivative chromosome 22 and the son inherited chromosome 15 and derivative chromosome 15. The family is unique in that two distinctive genetic syndromes, 22q11.2 deletion syndrome and Angelman syndrome, occurred within the same family. The family is also elucidative from an educational standpoint in that major concepts of non-Mendelian inheritance (microdeletion, genomic imprinting, and reciprocal translocation) need to be considered to appreciate the inheritance pattern. Furthermore, the family illustrates the importance of cryptic rearrangements at the most proximal end of acrocentric chromosomes in the evaluation of siblings with multiple congenital anomaly-mental retardation phenotypes that are dissimilar among affected siblings. The situation is analogous to parental balanced translocation between the most "distal" segments of a chromosome, that is, the subtelomere region, a recently appreciated cause of familial recurrence of multiple congenital anomaly-mental retardation phenotype with a normal G-banding karyotype. We suggest that cryptic rearrangements at the most proximal end, analogous to those at the most distal end, should be considered as an appreciable cause of recurrent multiple congenital anomaly-mental retardation phenotype.

Molecular mechanisms and diagnosis of chromosome 22q11.2 rearrangements

Several recurrent, constitutional genomic disorders are present on chromosome 22q. These include the translocations and deletions associated with DiGeorge and velocardiofacial syndrome and the translocations that give rise to the recurrent t(11;22) supernumerary der(22) syndrome (Emanuel syndrome). The rearrangement breakpoints on 22q cluster around the chromosome-specific segmental duplications of proximal 22q11, which are involved in the etiology of these disorders. While the deletions are the result of nonallelic homologous recombination (NAHR) between low copy repeats or segmental duplications within 22q11, the t(11;22) is the result of rearrangement between palindromic AT-rich repeats on 11q and 22q. Here we describe the mechanisms responsible for these recurrent rearrangements, discuss the recurrent deletion endpoints that are the result of NAHR between chromosome 22q specific low copy repeats as well as present current diagnostic approaches to deletion detection.

Detailed analysis of 22q11.2 with a high density MLPA probe set

The presence of chromosome-specific low-copy repeats (LCRs) predisposes chromosome 22 to deletions and duplications. The current diagnostic procedure for detecting aberrations at 22q11.2 is chromosomal analysis coupled with fluorescence in situ hybridization (FISH) or PCR-based multiplex ligation dependent probe amplification (MLPA). However, there are copy number variations (CNVs) in 22q11.2 that are only detected by high-resolution platforms such as array comparative genomic hybridization (aCGH). We report on development of a high-definition MLPA (MLPA-HD) 22q11 kit that detects copy number changes at 37 loci on the long arm of chromosome 22. These include the 3-Mb region commonly deleted in DiGeorge/velocardiofacial syndrome (DGS/VCFS), the cat eye syndrome (CES) region, and more distal regions in 22q11 that have recently been shown to be deleted. We have used this MLPA-HD probe set to analyze 363 previously well-characterized samples with a variety of different rearrangements at 22q11 and demonstrate that it can detect copy number alterations with high sensitivity and specificity. In addition to detection of the common recurrent deletions associated with DGS/VCFS, variant and novel chromosome 22 aberrations have been detected. These include duplications within as well as deletions distal to this region. Further, the MLPA-HD detects deletion endpoint differences between patients with the common 3-Mb deletion. The MLPA-HD kit is proposed as a cost effective alternative to the currently available detection methods for individuals with features of the 22q11 aberrations. In patients with the relevant phenotypic characteristics, this MLPA-HD probe set could replace FISH for the clinical diagnosis of 22q11.2 deletions and duplications.

A 21 years follow-up of a girl patient with a pseudodicentric bisatellited chromosome 22 associated with partial trisomy 22pter-->22q12.1: clinical, cytogenetic and molecular observations

We present clinical and developmental data on a patient with a de novo recombinant pseudodicentric bisatellited chromosome 22 associated with a partial trisomy 22pter-22q12.1. The patient was evaluated at birth and followed-up until 21 years of age. Clinical findings include facial and digital dysmorphism, hydrocephalus and postnatal-onset growth deficiency. The patient showed bilateral microphthalmia with severe palpebral ptosis and coloboma of the iris and left optic nerve. She also has skeletal and neurological abnormalities, cholesteatoma and seizures. She had absence of speech, poor mobility, poor vision and required help with all daily living skills. Conventional chromosome GTG banded analysis showed that the proband had an abnormal karyotype:46,XX,add(22)(q13). Fluorescence in situ hybridization (FISH) analyses and microsatellite markers for DNA polymorphism study ascertained the karyotype as 46,XX,add(22)(q13.3).ish psu dic(22;22)(q13.3;q12.1)(D14Z1/D22Z1++, N25++, ARSA+, PCP22q+). The recombinant chromosome was stable and present in all cells examined. The paternal origin of the psu dic(22;22) chromosome was determined by using five highly polymorphic microsatellite markers located to the region of chromosome 22q11.2-22q13.33. A 22q13.3 monosomy was ruled out with 22q13.3 cosmid probes covering the terminal 22q-140Kb. The proband carried a recombinant pseudodicentric bisatellited chromosome psu dic(22;22)(q13.3;q12.1). To our knowledge, this is the first report of such rearrangement resulting in partial trisomy 22pter-22q12.1.

A palindrome-driven complex rearrangement of 22q11.2 and 8q24.1 elucidated using novel technologies

Constitutional translocations at the same 22q11.21 low copy repeat B (LCR-B) breakpoint involved in the recurrent t(11;22) are relatively abundant. A novel 46,XY,t(8;22)(q24.13;q11.21) rearrangement was investigated to determine whether the recurrent LCR-B breakpoint is involved. Investigations demonstrated an inversion of the 3Mb region typically deleted in patients with the 22q11.2 deletion syndrome. The 22q11.21 inversion appears to be mediated by low copy repeats, and is presumed to have taken place prior to translocation with 8q24.13. Despite predictions based on inversions observed in other chromosomes harboring low copy repeats, this 22q11.2 inversion has not been observed previously. The current studies utilize novel laser microdissection and MLPA (multiplex ligation-dependent probe amplification) approaches, as adjuncts to FISH, to map the breakpoints of the complex rearrangements of 22q11.21 and 8q24.21. The t(8;22) occurs between the recurrent site on 22q11.21 and an AT-rich site at 8q24.13, making it the fifth different chromosomal locus characterized at the nucleotide level engaged in a translocation with the unstable recurrent breakpoint at 22q11.21. Like the others, this breakpoint occurs at the center of a palindromic sequence. This sequence appears capable of forming a perfect 145 bp stem-loop. Remarkably, this site appears to have been involved in a previously reported t(3;8) occurring between 8q24.13 and FRA3B on 3p14.2. Further, the fragile site-like nature of all of the breakpoint sites involved in translocations with the recurrent site on 22q11.21, suggests a mechanism based on delay of DNA replication in the initiation of these chromosomal rearrangements.

Trisomy of 19.4 Mb region of chromosome 22 and subtelomeric 17p identified in a male without clinical affectation

Supernumerary marker chromosomes (SMCs) have a reported frequency in the prenatal and newborn population ranging from 0.04% to 0.08% and about 37% of diagnosed SMCs are associated with an abnormal phenotype. Around 7.5% of them are derived from chromosome 22. SMCs(22) that result in tri- or tetrasomy of band 22q11.2 are associated with Cat-eye syndrome (CES), a syndrome of variable penetrance and affectation. CES-like phenotype has been also related to 22q11.2 interstitial duplications and der(22) syndrome. The 22q11.2 region, also involved in the velocardiofacial microdeletional syndrome, presents high susceptibility to chromosomal rearrangements due to the presence of low-copy repeats sequences (LCR22). Another region in the genome rich in LCR is 17p and five recurrent disorders have been mapped on the region 17p11-p13. Some chromosomal imbalances affecting the 17p13.3 subtelomeric region have been reported, related to cryptic unbalanced translocations and associated, in most cases, to mental retardation and dysmorphic features. We report on a healthy male carrier of a SMC that was identified as a +der(22)t(17;22)(p13.3;q11.2) consequence of an abnormal 3:1 segregation of the paternal t(17;22) and we have determined the approximate size of the trisomic regions, comparing the obtained results with other reported imbalances involving 22q11.2 and 17pter.

Uveal coloboma: clinical and basic science update

PURPOSE OF REVIEW

To integrate knowledge on the embryologic and molecular basis of optic fissure closure with clinical observations in patients with uveal coloboma.

RECENT FINDINGS

Closure of the optic fissure has been well characterized and many genetic alterations have been associated with coloboma; however, molecular mechanisms leading to coloboma remain largely unknown. In the past decade, we have gained better understanding of genes critical to eye development; however, mutations in these genes have been found in few individuals with coloboma. CHD7 mutations have been identified in patients with CHARGE syndrome (coloboma, heart defects, choanal atresia, retarded growth, genital anomalies, and ear anomalies or deafness). Animal models are bringing us closer to a molecular understanding of optic fissure closure.

SUMMARY

Optic fissure closure requires precise orchestration in timing and apposition of two poles of the optic cup. The relative roles of genetics and environment on this process remain elusive. While most cases of coloboma are sporadic, autosomal dominant, autosomal recessive, and X-linked inheritance patterns have been described. Genetically, colobomata demonstrate pleiotropy, heterogeneity, variable expressivity, and reduced penetrance. Coloboma is a complex disorder with a variable prognosis and requires regular examination to optimize visual acuity and to monitor for potential complications.

Human ADA2 belongs to a new family of growth factors with adenosine deaminase activity

Two distinct isoenzymes of ADA (adenosine deaminase), ADA1 and ADA2, have been found in humans. Inherited mutations in ADA1 result in SCID (severe combined immunodeficiency). This observation has led to extensive studies of the structure and function of this enzyme that have revealed an important role for it in lymphocyte activation. In contrast, the physiological role of ADA2 is unknown. ADA2 is found in negligible quantities in serum and may be produced by monocytes/macrophages. ADA2 activity in the serum is increased in various diseases in which monocyte/macrophage cells are activated. In the present study, we report that ADA2 is a heparin-binding protein. This allowed us to obtain a highly purified enzyme and to study its biochemistry. ADA2 was identified as a member of a new class of ADGFs (ADA-related growth factors), which is present in almost all organisms from flies to humans. Our results suggest that ADA2 may be active in sites of inflammation during hypoxia and in areas of tumour growth where the adenosine concentration is significantly elevated and the extracellular pH is acidic. Our finding that ADA2 co-purified and concentrated together with IgG in commercially available preparations offers an intriguing explanation for the observation that treatment with such preparations leads to non-specific immune-system stimulation.

FISH of supernumerary marker chromosomes (SMCs) identifies six diagnostically relevant intervals on chromosome 22q and a novel type of bisatellited SMC(22)

Supernumerary marker chromosomes (SMCs) are frequently found at pre- and postnatal cytogenetic diagnosis and require identification. A disproportionally large subset of SMCs is derived from the human chromosome 22 and confers tri- or tetrasomy for the cat eye chromosomal region (CECR, the proximal 2 Mb of chromosome 22q) and/or other segments of 22q. Using fluorescence in situ hybridization (FISH) and 15 different DNA probes, we studied nine unrelated patients with an SMC(22) that contained the CECR. Five patients showed the small (type I) cat eye syndrome (CES) chromosome and each one had the larger (type II) CES chromosome, small ring chromosome 22, der(22)t(11;22) extrachromosome, and a novel type of bisatellited SMC(22) with breakpoints outside the low-copy repeats (LCRs22). By size and morphology, the novel bisatellited SMC(22) resembled the typical (types I and II) CES chromosomes, but it might have been associated with the chromosome 22q duplication syndrome, not CES. This SMC included a marker from band 22q12.3 and conferred only one extra copy each of the 22 centromere, CECR, and common 22q11 deletion area. There has been no previous report of a bisatellited SMC(22) predicting the chromosome 22q duplication syndrome. Accounting for the cytogenetic resemblance to CES chromosomes but different makeup and prognosis, we propose naming this an atypical (type III) CES chromosome. In this study, we found six distinct intervals on 22q to be relevant for FISH diagnostics. We propose to characterize SMCs(22) using DNA probes corresponding to these intervals.

Microduplication 22q11.2, an emerging syndrome: clinical, cytogenetic, and molecular analysis of thirteen patients

Chromosome 22, particularly band 22q11.2, is predisposed to rearrangements due to misalignments of low-copy repeats (LCRs). DiGeorge/velocardiofacial syndrome (DG/VCFS) is a common disorder resulting from microdeletion within the same band. Although both deletion and duplication are expected to occur in equal proportions as reciprocal events caused by LCR-mediated rearrangements, very few microduplications have been identified. We have identified 13 cases of microduplication 22q11.2, primarily by interphase fluorescence in situ hybridization (FISH). The size of the duplications, determined by FISH probes from bacterial artificial chromosomes and P(1) artificial chromosomes, range from 3-4 Mb to 6 Mb, and the exchange points seem to involve an LCR. Molecular analysis based on 15 short tandem repeats confirmed the size of the duplications and indicated that at least 1 of 15 loci has three alleles present. The patients' phenotypes ranged from mild to severe, sharing a tendency for velopharyngeal insufficiency with DG/VCFS but having other distinctive characteristics, as well. Although the present series of patients was ascertained because of some overlapping features with DG/VCF syndromes, the microduplication of 22q11.2 appears to be a new syndrome.