Ring 20 chromosome phenotype

Case Report: A Paternal 20q13.2-q13.32 Deletion Patient With Growth Retardation Improved by Growth Hormone

Interstitial chromosome 20q deletions, containing GNAS imprinted locus, are rarely reported in the past. Hereby, we presented a Chinese boy with a novel 4.36 Mb deletion at paternal 20q13.2-13.32, showing feeding difficulty, malnutrition, short stature, lower limb asymmetry, sightly abnormal facial appearance and mild intellectual abnormality. With 3 years’ growth hormone treatment, his height was increased from 90 to 113.5 cm. This report is the first time to describe the outcome of clinical treatment on a patient with this rare chromosomal 20 long arm interstitial deletion, containing GNAS locus, which may facilitate the diagnosis and treatment of this type of patient in the future.

Specificity of electroclinical features in the diagnosis of ring chromosome 20

BACKGROUND

Ring chromosome 20 (R20) syndrome is a chromosomal disorder characterized mainly by drug-resistant frontal lobe seizures, recurrent nonconvulsive status epilepticus (NCSE), and typical EEG features. The aim of this study was to investigate if this triad is common and specific to all patients with R20.

METHODS

In this cross-sectional study (from 2000 to 2011), we selected patients who fulfilled at least two out of three criteria: drug-resistant frontal lobe seizures, recurrent NCSE, and characteristic electroencephalography (EEG) features. In all patients, diagnosis was based on karyotype analysis of at least 100 metaphases.

RESULTS

We identified 36 patients who met at least two of the selected criteria: six patients (16.7%) with R20 and 30 (83.3%) without R20 (non-R20). All patients with R20 met all three criteria. Eleven (36.7%) patients without R20, however, also displayed the full triad. In 19 patients without R20 (63.3%), one of the three clinical features was missing: frontal lobe seizures were not resistant to antiepileptic drugs (AED) in four (13.3%), recurrent NCSE was missing in six (20%), and nine (30%) patients did not have typical EEG features. Based on this data, specificity was 63.3%, positive predictive value was 35.3%, and sensitivity and negative predictive values were 100%. Additionally, a review of all publications describing the R20 phenotype revealed that 81.98% of patients with R20 display the full electroclinical triad.

CONCLUSIONS

In our study, all patients with R20 displayed the three electroclinical characteristics. This is in line with previous reports (presenting high sensitivity and negative predictive value). However, these features can also be observed in other epilepsies and are not specific to R20. Our findings suggest that in the presence of the full triad of symptoms, karyotype analysis focused on chromosome 20 should be conducted.

Subtelomeric FISH analysis in 76 patients with syndromic developmental delay/intellectual disability

BACKGROUND

Intellectual disability affects approximately 1 to 3% of the general population. The etiology is still poorly understood and it is estimated that one-half of the cases are due to genetic factors. Cryptic subtelomeric aberrations have been found in roughly 5 to 7% of all cases.

METHODS

We performed a subtelomeric FISH analysis on 76 unrelated children with normal standard karyotype ascertained by developmental delay or intellectual disability, associated with congenital malformations, and/or facial dysmorphisms.

RESULTS

Ten cryptic chromosomal anomalies have been identified in the whole cohort (13,16%), 8 in the group of patients characterized by developmental delay or intellectual disability associated with congenital malformations and facial dysmorphisms, 2 in patients with developmental delay or intellectual disability and facial dysmorphisms only.

CONCLUSION

We demonstrate that a careful clinical examination is a very useful tool for pre-selection of patients for genomic analysis, clearly enhancing the chromosomal anomaly detection rate. Clinical features of most of these patients are consistent with the corresponding emerging chromosome phenotypes, pointing out these new clinical syndromes associated with specific genomic imbalances.

Major feeding difficulties in the first reported case of interstitial 20q11.22-q12 microdeletion and molecular cytogenetic characterization

We report on a 4-year-old female presenting with intrauterine growth retardation, facial dysmorphic features, major feeding difficulties with severe diarrhea and vomiting, mental retardation with abnormal behavior and hypertonia. Feeding difficulties were the most invalidating features with absent oral intake requiring persistent enteral feeding. Standard cytogenetic studies were normal, but high-resolution chromosome analyses revealed a small de novo interstitial deletion of the long arm of chromosome 20, 46,XX,del(20)(q11.21q12). The deletion was confirmed using metaphase comparative genomic hybridization (CGH) and multicolor high resolution banding (mBAND). The deletion breakpoints were characterized using FISH analyses with YACs, PACs, and BACs clones located in the deleted and adjacent regions. A 6.6-Mb deleted region between markers D20S815 (20q11.22) and D20S435 (20q12) could be delineated. None of the nine previously reported cases with interstitial 20q deletion found in the literature involve the same breakpoints. This report further emphasizes the indication of high-resolution chromosome analyses in children with syndromic mental retardation. The description of additional cases would be useful in order to better characterize the phenotype of patients with proximal interstitial 20q deletion.

Early pattern of epilepsy in the ring chromosome 20 syndrome

PURPOSE

The characteristics of epilepsy in ring chromosome 20 have been reported in adolescents and adults. The mode of onset most often remains imprecise. To clarify this onset period, we studied the early-onset features in our personal series and in the reported pediatric cases.

METHODS

Our series comprises one child with an onset of epilepsy in the neonatal period and five others with an onset before age 8 years. The cases in the literature with an epilepsy onset before 8 years also were reviewed.

RESULTS

Seizures in the neonatal period were described as motor seizures. Our personal patient with a neonatal onset had severe psychomotor delay. In both infancy and early childhood, the EEG showed no interictal frontal localization of the anomalies, and no long-lasting seizure was recorded. Seizures with terror and hallucinations usually appeared from about age 4 years. It is not before the age of 8 years that the usual interictal EEG pattern appeared of rhythmic theta slow-waves activity with spikes predominating in frontal areas described in adolescence and adulthood. The interictal EEG showed 1- to 2-Hz delta slow waves and spike-and-waves predominating in frontal areas, but no physiologic activity.

CONCLUSIONS

In ring 20 chromosome, specific epilepsy features are lacking in the neonate, but the whole phenotype shows a more severe expression in terms of mental delay. The characteristic frontal EEG pattern and ictal terror do not appear before age 4 to 5 years.

Perinatal findings and molecular cytogenetic analysis of de novo partial trisomy 16q (16q22.1-->qter) and partial monosomy 20q (20q13.3-->qter)

OBJECTIVES

To present the perinatal findings and molecular cytogenetic analysis of de novo partial trisomy 16q and partial monosomy 20q and a review of the literature.

CASE AND METHODS

Obstetric ultrasound at 33 weeks' gestation revealed intrauterine growth restriction (IUGR) and dolichocephaly in a 27-year-old primigravid woman. Prenatal cytogenetic diagnosis was not offered because of the late stage of gestation. A 2800-g male baby was delivered at 41 weeks' gestation by cesarean section because of fetal distress. The infant postnatally presented characteristic craniofacial dysmorphism, hypotonia, cleft palate, congenital heart defects, a subependymal cyst, and hypospadia. Cytogenetic analysis revealed an additional material attached to the terminal region of chromosome 20q. The parental karyotypes were normal. Spectral karyotyping (SKY), fluorescence in situ hybridization (FISH), and polymorphic DNA markers were used to investigate the origin of the de novo aberrant chromosome.

RESULTS

SKY using 24-color probes, FISH using specific 16p, 16q, 20 centromeric, and 20q telomeric probes, and polymorphic DNA marker analysis confirmed maternal origin of the duplication of distal 16q and the deletion of terminal 20q. Karyotype of the proband was designated as 46,XY.ish der(20)t(16;20)(q22.1;q13.3)(SKY+,16qTEL+,20qTEL-).

CONCLUSIONS

Partial trisomy 16q (16q22.1-->qter) and partial monosomy 20q (20q13.3-->qter) may be associated with the perinatal findings of IUGR, dolichocephaly, hypotonia, cleft palate, congenital heart defects, a subependymal cyst, and hypospadia. SKY, FISH, and genetic marker studies help in delineating the parental origin and the regions of the deletion and duplication in the de novo unbalanced translocation.

Paternal deletion of the GNAS imprinted locus (including Gnasxl) in two girls presenting with severe pre- and post-natal growth retardation and intractable feeding difficulties

Deletions of the long arm of chromosome 20 are rare. Here, we report on two girls with a very small interstitial deletion of the long arm of chromosome 20 presenting with severe pre- and post-natal growth retardation, intractable feeding difficulties, abnormal subcutaneous adipose tissue, similar facial dysmorphism, psychomotor retardation and hypotonia. Standard cytogenetic studies were normal, but high-resolution chromosomes analysis showed the presence of a chromosome (20)(q13.2-q13.3) interstitial deletion. Karyotypes of both parents were normal. Molecular studies using FISH and microsatellite polymorphic markers showed that the deletion was of paternal origin and was approximatively 4.5 Mb in size. A review of other reported patients with similar deletions of the long arm of chromosome 20 shows that the observed phenotype might be explained in the light of the GNAS imprinted locus in particular by the absence of the Gnasxl paternally imprinted gene and the TFA2PC gene in the deleted genetic interval.

Constitutional deletion of chromosome 20q in two patients affected with albright hereditary osteodystrophy

Albright hereditary osteodystrophy (AHO) results from heterozygous inactivation of G(s)alpha, encoded by the GNAS1 locus on the distal long arm of chromosome 20. This autosomal dominant condition is characterized by short stature, obesity, shortening of the metacarpals and metatarsals, and variable mental retardation and may also include end-organ resistance to multiple hormones. Small insertions and deletions or point mutations of GNAS1 are found in approximately 80% of patients with AHO. The remainder may be accounted for by larger genomic rearrangements, but none have been reported to date. We now describe two patients with constitutional 20q deletions and features of AHO. Such deletions are rare in the published literature and have not previously been associated with AHO. Molecular genetic analysis confirmed complete deletion of GNAS1 in both patients. Parental origin could be determined in both cases and provides further support for the parent-of-origin effect on the biochemical status of patients with AHO.

Epilepsy and ring chromosome 20: case report

We present the clinical, electroencephalographic, neuroimaging (brain magnetic resonance image - MRI and spectroscopy by MRI) and cytogenetic findings of a young male patient with a rare cytogenetic anomaly characterised by a de novo 46,XY,r(20)(p13q13.3) karyotype. He presents with mental retardation, emotional liability, and strabismus, without any other significant dysmorphies. There are brain anomalies characterised by corpus callosum, uvula, nodule and cerebellum pyramid hypoplasias, besides arachnoid cysts in the occipital region. He had seizures refractory to pharmacotherapy and long period of confusional status with or without a motor component. The authors recognised that the EEG pattern was not fixed but changed over time, specially for bursts of slow waves with great amplitude accompanied or not by sharp components, and bursts of theta waves sharply contoured. Previously, epilepsy solely has been assigned to region 20q13. However, the important structural cerebral alterations present in our case has not been reported associated to such chromosomal abnormality and may indicate possible new chromosomal sites where such atypical neurological characteristics could be mapped.

Chromosomal abnormalities and epilepsy: a review for clinicians and gene hunters

PURPOSE

We analyzed databases on chromosomal anomalies and epilepsy to identify chromosomal regions where abnormalities are associated with clinically recognizable epilepsy syndromes. The expectation was that these regions could then be offered as targets in the search for epilepsy genes.

METHODS

The cytogenetic program of the Oxford Medical Database, and the PubMed database were used to identify chromosomal aberrations associated with seizures and/or EEG abnormalities. The literature on selected small anomalies thus identified was reviewed from a clinical and electroencephalographic viewpoint, to classify the seizures and syndromes according to the current International League Against Epilepsy (ILAE) classification.

RESULTS

There were 400 different chromosomal imbalances described with seizures or EEG abnormalities. Eight chromosomal disorders had a high association with epilepsy. These comprised: the Wolf-Hirschhorn (4p-) syndrome, Miller-Dieker syndrome (del 17p13.3), Angelman syndrome (del 15q11-q13), the inversion duplication 15 syndrome, terminal deletions of chromosome 1q and 1p, and ring chromosomes 14 and 20. Many other segments had a weaker association with seizures. The poor quality of description of the epileptology in many reports thwarted an attempt to make precise karyotype-phenotype correlations.

CONCLUSIONS

We identified certain chromosomal regions where aberrations had an evident association with seizures, and these regions may be useful targets for gene hunters. New correlations with specific epilepsy syndromes were not revealed. Clinicians should continue to search for small chromosomal abnormalities associated with specific epilepsy syndromes that could provide important clues for finding epilepsy genes, and the epileptology should be rigorously characterized.

Ring-20-syndrome and loss of telomeric regions

A patient aged 10 years and 8 months with a ring-20-syndrome was studied. Clinically he presented normal psychomotor development until 25 months of age when he began with right simple partial motor seizures. He presented minimal dysmorphism, generalized tonic-clonic seizures refractory to medical therapy and behavioral troubles. He was submitted to a callosotomy when he presented an electric status, subsequently, he was treated with anticonvulsivants and felbamate and the seizures were controlled. The karyotype showed a chromosomal complement 46,XY,r(20)(p13q13.3) with loss of the telomeric regions evidenced by FISH. The mother had normal karyotype. The clinical and cytogenetic features of previous cases described in the literature were compared leading to a better characterization of this syndrome.

Characteristic EEG findings in ring 20 syndrome as a diagnostic clue

OBJECTIVE

To review the EEG features of ring 20 syndrome in two patients and determine the characteristic pattern of this syndrome. The features of our cases and 24 patients reported in the literature will be discussed.

SUBJECTS AND METHODS

Report of two patients and review of literature.

RESULTS

The two patients had intractable epilepsy since childhood. Their clinical seizures were mostly complex partial seizures. Often the patients seizures were of prolonged duration. Ictal EEG revealed characteristic slow waves, and sharp waves. The slow waves were (1) usually synchronous high-voltage slow waves with or without a spike component predominantly in the frontal and frontopolar areas, (2) sometimes showed a change in frequency every several seconds, (3) continued for a long period, and (4) easily spread diffusely. The sharp waves were 5-6 Hz irregular and diffuse discontinuous sharp waves, and sometimes appeared predominantly in the centroparietal area. The clinical seizure pattern and EEG findings were similar in the 24 published cases.

CONCLUSIONS

These EEG findings may be a characteristic feature of ring 20 syndrome and thus may be useful as a diagnostic clue.

Chromosome 20 ring: a chromosomal disorder associated with a particular electroclinical pattern

PURPOSE

The chromosome 20 ring [r(20)] is a rare chromosomal disorder without clear phenotypical markers. We describe the electroclinical pattern in a group of patients with r(20).

METHODS

We observed 3 patients (a boy, patient 1; his mother, patient 2; and an unrelated man, patient 3), performing prolonged video-EEG and cytogenetic studies and fluorescent in situ hybridization (FISH) with chromosome-specific telomeric probes.

RESULTS

All 3 patients had a very similar abnormal electroclinical pattern characterized by long bursts or trains of rhythmic theta waves, which were sharply contoured or had a notched appearance (with no detectable clinical correlate), and generalized spike waves (SW) associated with seizures of probable frontotemporal origin (SFT). In all 3 patients, the cytogenetic analysis of T lymphocytes showed mosaicism with a normal cell line and a second cell line with a chromosome 20, although the latter was little represented in patients 2 and 3. A few cells with a single chromosome 20 were also found. The same cytogenetic findings were confirmed in the lymphoblastoid cell line of patient 1 and in the fibroblasts of patient 3. FISH with chromosome-specific telomeric probes and TTAGGG sequences demonstrated the integrity of the ring chromosomes.

CONCLUSIONS

The clinical picture of these patients appears to be related to the instability of the r(20)-generating cells monosomic for chromosome 20 and is thus haploinsufficient for a gene. In these patients, the electroclinical pattern of theta waves (probably unrelated to epilepsy) and the SW and SFT, even with mild mental retardation (MR) or no MR and without dysmorphic features, suggest that the r(20) syndrome may be present.

A study of ring 20 chromosome karyotype with epilepsy

We reported a 24-year-old woman with moderate mental retardation and partial epilepsy. She developed complex partial seizures at 3 years of age and generalized tonic convulsions at 9 years. Chromosome analysis revealed that she had mosaicism (87%) of 46, XX, and r(20) (p13,q13.3). Her electroencephalogram showed bilateral 2-3 Hz sharp and wave complex over the bilateral frontopolar, and centro-parieto-occipital areas. Computed tomographic and magnetic resonance image examinations were normal. Twenty-five cases of ring 20 chromosome karyotypes (including this case) have been reported in the literature; 19 showed epilepsy, and 18 showed moderate mental retardation. Many of the patients showed growth retardation and minor malformations. The ring 20 syndrome is associated with a high incidence of epilepsy, particularly partial epilepsy. Our findings indicate that the main features of the ring 20 syndrome are partial epilepsy and mental retardation.

Hypertelorism and hypospadias associated with a de novo apparently balanced translocation between 8q22.3-23 and 20p13

A de novo apparently balanced translocation involving chromosomes 8 and 20 was found in a 14-year-old boy with minor anomalies, mild skeletal abnormalities and ambiguous external genitalia including perineoscrotal hypospadias, rudimentary fused labioscrotal folds, bilateral cryptorchidism, and small penis. The karyotype was 46,XY, t(8;20)(q22.3-23;p13). No signs of other conditions known to be associated with structural anomalies of either chromosome 8 or 20 were present and incomplete masculinisation of the external genitalia appears to be the main component of the phenotype. Clinical and biological studies showed apparently normal testicular function in utero and after birth. Examinations excluded 5 alpha-reductase deficiency or a block in any enzymatic steps of testosterone, glucocorticoid and mineralocorticoid biosynthesis. Coding sequences of the sex-determining gene (SRY) and androgen receptor gene (AR) were found to be identical to those of a normal male excluding their role in the cause of the present condition. Since several other reports describe the association of hypospadias and hypertelorism with deletions or translocations involving 8q, we suggest that a locus necessary for male sex differentiation is located at distal 8q.

Duplication of 7p: further delineation of the phenotype and restriction of the critical region to the distal part of the short arm

We report on a patient with duplication of 7p15-->pter and review the literature. Patients with partial duplication of the distal 7p, including only the distal segment 7p15-->pter, have a syndrome comparable to that of patients with a larger or complete duplication of 7p. This suggests that the critical region for the dup(7p) phenotype is restricted to 7p15-->pter. The complete clinical phenotype of dup(7)(p15-->pter) includes mental retardation, skull anomalies, large anterior fontanel, cardiovascular defects, joint dislocation and contraction, and gastrointestinal and genital defects. Recognition of the clinical spectrum in patients with a smaller duplication of 7p, and the assignment of this critical region, should prove valuable for accurate counseling, prediction of outcome, and further gene mapping.

Nonphotosensitive video game-induced partial seizures

We report a 9-year-old boy with a ring 20 chromosome anomaly whose complex partial seizures (CPS), presumably of frontal lobe origin, were often induced by playing video games. Neither photosensitivity nor pattern sensitivity was observed. An intensive video-EEG investigation showed that video games as well as mental calculation elicited rhythmic runs of bilateral high-voltage slow waves, which eventually evolved into ictal discharges. This case suggests that higher brain functions can be involved in seizure induction.

Ring chromosome 20 with loss of telomeric sequences detected by multicolour PRINS

A ring chromosome 20 in a male infant with epileptic seizures, mental and somatic growth retardation, and behavioural disturbances is described. Conventional cytogenetics revealed the karyotype to be 46,XY,r(20)(pter-->qter) and no signs of mosaicism were found. Fluorescence in situ hybridisation using the clone p20Z1 identified the ring to be derived from chromosome 20. By counting 111 metaphases, only 7% were found to be missing the ring. The absence of telomeric sequences in the ring chromosome was demonstrated by multicolour PRINS: a three-step PRimed IN Situ labelling technique, using unlabelled primers. A terminal deletion of both arms thus seems to be the cause of the ring formation in the proband. Bivariate flow-analysis of chromosomes verified a deletion of the ring chromosome. The clinical and cytogenetic findings are compared with previous cases. A specific ring 20 syndrome seems justified.

Chromosome 20 long arm deletion in an elderly malformed man

A 46,XY/46,XY,del(20)(q13-->q13.33) mosaicism was identified in a 68 year old man who had mild mental retardation and severe malformation of the limbs. The clinical findings of the patient are compared to those of the very few cases of 20q deletion published to date.

Ring chromosome 20 and possible assignment of the structural gene encoding human carboxypeptidase-L to the distal segment of the long arm of chromosome 20

We report on a 14-year-old boy with ring chromosome 20. Clinical manifestations included postnatal growth retardation, epilepsy, microcephaly, behaviour disorder, minor facial anomalies, small sella turcica, possible partial growth hormone deficiency, and mental retardation. A decreased activity of enzyme carboxypeptidase-L/protective protein (CP/PP) in cultured fibroblasts was demonstrated in our patient and a patient with a karyotype 46,XY,-14, + der(14)t(14;20)(14pter----14q32.3::20q13.1----20qter)m at. This suggests possible assignment of the CP/PP gene to the distal segment of 20q.

Familial ring (20) chromosomal mosaicism

Ring (20) chromosomal mosaicism defined by two cell lines (one normal and the other with the ring) has been demonstrated in lymphocyte and fibroblast cultures from three members of a family through two generations. Two carriers of the ring chromosome were affected and showed the typical signs of r(20) syndrome including mental retardation, microcephaly, behavioral disorders, and epilepsy. The epilepsy is characterized by complex partial seizures sometimes evolving secondarily into generalized tonic-clonic seizures and is poorly controlled by or resistant to medical treatment. The mother of the two patients, also a carrier of ring (20) chromosomal mosaicism, was clinically and phenotypically normal and did not exhibit any signs of epilepsy. Lymphocyte and fibroblast cultures from the most severely affected sib, the proband, contained the highest percentage of cells with ring (20) chromosome and revealed the greatest instability of the ring. Though it is assumed that the ring (20) chromosome arose from terminal breakage and reunion in both arms, no loss of genetic material could be documented cytogenetically. Yet the question arises of how ring chromosomal mosaicism can be passed on. One explanation might be that a chromosome 20 predisposed to terminal lesions or breaks is transmitted from the mother to her offspring. Inherited instability of this type might lead to de novo formation of the ring.