A girl with 15q overgrowth syndrome and dup(15)(q24q26.3) that included telomeric sequences

Chromosomal Microarray Analysis in Turkish Patients with Unexplained Developmental Delay and Intellectual Developmental Disorders

INTRODUCTION

Aneuploids, copy number variations (CNVs), and single nucleotide variants in specific genes are the main genetic causes of developmental delay (DD) and intellectual disability disorder (IDD). These genetic changes can be detected using chromosome analysis, chromosomal microarray (CMA), and next-generation DNA sequencing techniques. Therefore; In this study, we aimed to investigate the importance of CMA in determining the genomic etiology of unexplained DD and IDD in 123 patients.

METHOD

For 123 patients, chromosome analysis, DNA fragment analysis and microarray were performed. Conventional G-band karyotype analysis from peripheral blood was performed as part of the initial screening tests. FMR1 gene CGG repeat number and methylation analysis were carried out to exclude fragile X syndrome.

RESULTS

CMA analysis was performed in 123 unexplained IDD/DD patients with normal karyotypes and fragile X screening, which were evaluated by conventional cytogenetics. Forty-four CNVs were detected in 39 (39/123=31.7%) patients. Twelve CNV variant of unknown significance (VUS) (9.75%) patients and 7 CNV benign (5.69%) patients were reported. In 6 patients, one or more pathogenic CNVs were determined. Therefore, the diagnostic efficiency of CMA was found to be 31.7% (39/123).

CONCLUSION

Today, genetic analysis is still not part of the routine in the evaluation of IDD patients who present to psychiatry clinics. A genetic diagnosis from CMA can eliminate genetic question marks and thus alter the clinical management of patients. Approximately one-third of the positive CMA findings are clinically intervenable. However, the emergence of CNVs as important risk factors for multiple disorders increases the need for individuals with comorbid neurodevelopmental conditions to be the priority where the CMA test is recommended.

Prenatal diagnosis of a de novo tetrasomy 15q24.3-25.3: Case report and literature review

BACKGROUND

Terminal duplication on chromosome 15q is a rare chromosomal variation. Affected individuals show similar features such as growth dysplasia or the development of frontal bossing, body deformities, facial abnormalities, and genitourinary or cardiovascular disorders. However, it is not yet clear whether such 15q repeats lead to identifiable patterns of clinical abnormalities. Therefore, the purpose of this study was to analyze the prenatal diagnostic results and clinical manifestations of a fetus with 15q duplication and to summarize the literature.

METHODS

The case was a fetus at 28 weeks of gestation. The risk of Down syndrome from second-trimester screening was 1/140. Prenatal ultrasound and amniocentesis were performed, and chromosomal microarray analysis (CMA) was used for genetic analysis.

RESULTS

The fetus had abnormal clinical features, including intracardiac echogenic focus in the left ventricle, an aberrant right subclavian artery, and growth delay. The fetal chromosomal karyotype was 46,XX,15q?,12q?,21pstk+, and CMA revealed a 10.163 Mb duplication at 15q24.3-q25.3. The couple chose to terminate the pregnancy after careful consideration.

CONCLUSIONS

The combination and rational application of cytogenetics technology and molecular genetics technology such as CMA will open up the field of clinical application and provide useful genetic counseling for parents of fetuses carrying such chromosomal duplications.

Prenatal diagnosis and molecular cytogenetic characterization of a de novo duplication of 15q24.3-q26.1

Reported cases of distal 15q interstitial duplications are uncommon and do not result in a recognizable pattern of abnormalities. Some studies report prenatal overgrowth, while others describe growth retardation. We present molecular cytogenetic characterization of a 14 Mb interstitial duplication, encompassing 81 Online Mendelian Inheritance in Man (OMIM) genes, in a fetus with single umbilical artery and short limbs. We propose that growth restriction, previously described and present in our patient, may be due to duplication of a gene or genes contained in the 15q24 region.

Chromosome 15 structural abnormalities: effect on IGF1R gene expression and function

Insulin-like growth factor 1 receptor (IGF1R), mapping on the 15q26.3 chromosome, is required for normal embryonic and postnatal growth. The aim of the present study was to evaluate the IGF1R gene expression and function in three unrelated patients with chromosome 15 structural abnormalities. We report two male patients with the smallest 15q26.3 chromosome duplication described so far, and a female patient with ring chromosome 15 syndrome. Patient one, with a 568 kb pure duplication, had overgrowth, developmental delay, mental and psychomotor retardation, obesity, cryptorchidism, borderline low testis volume, severe oligoasthenoteratozoospermia and gynecomastia. We found a 1.8-fold increase in the IGF1R mRNA and a 1.3-fold increase in the IGF1R protein expression (P < 0.05). Patient two, with a 650 kb impure duplication, showed overgrowth, developmental delay, mild mental retardation, precocious puberty, low testicular volume and severe oligoasthenoteratozoospermia. The IGF1R mRNA and protein expression was similar to that of the control. Patient three, with a 46,XX r(15) (p10q26.2) karyotype, displayed intrauterine growth retardation, developmental delay, mental and psychomotor retardation. We found a <0.5-fold decrease in the IGF1R mRNA expression and an undetectable IGF1R activity. After reviewing the previously 96 published cases of chromosome 15q duplication, we found that neurological disorders, congenital cardiac defects, typical facial traits and gonadal abnormalities are the prominent features in patients with chromosome 15q duplication. Interestingly, patients with 15q deletion syndrome display similar features. We speculate that both the increased and decreased IGF1R gene expression may play a role in the etiology of neurological and gonadal disorders.

Exome Sequencing of a Pedigree Reveals S339L Mutation in the TLN2 Gene as a Cause of Fifth Finger Camptodactyly

Camptodactyly is a digit deformity characterized by permanent flexion contracture of one or both fifth fingers at the proximal interphalangeal joints. Though over 60 distinct types of syndromic camptodactyly have been described, only one disease locus (3q11.2-q13.12) for nonsyndromic camptodactyly has been identified. To identify the genetic defect for camptodactyly in a four-generation Chinese Han family, exome and Sanger sequencings were conducted and a missense variant, c.1016C>T (p.S339L), in the talin 2 gene (TLN2) was identified. The variant co-segregated with disease in the family and was not observed in 12 unaffected family members or 1,000 normal controls, suggesting that p.S339L is a pathogenic mutation. Two asymptomatic carriers in the family indicated incomplete penetrance or more complicated compensated mechanism. Most of p.S339L carriers also have relatively benign cardiac phenotypes. Expression of wild and mutant TLN2 in HEK293 cells suggested the predominant localization in cytoplasm. Our data suggest a potential molecular link between TLN2 and camptodactyly pathogenesis.

Two familial microduplications of 15q26.3 causing overgrowth and variable intellectual disability with normal copy number of IGF1R

Terminal duplications of 15q26.3 are associated with an overgrowth phenotype, distinct facial features and intellectual disability, with the smallest reported microduplication to date being 3.16 Mb in size. We report two familial 15q26.3 microduplication cases that are less than half this size, re-defining the minimal critical region for this duplication syndrome. In both families the duplication (albeit a complex copy number gain in one family) is associated with tall stature, early speech delay and variable cognitive problems. Neither familial copy number gains encompass the gene encoding for the insulin-like growth factor 1 receptor (IGF1R), the most-cited candidate for the overgrowth phenotype. In one family, whole genome sequence data and break point mapping excludes disruption of known IGF1R regulatory elements due to potential insertion within these elements. These cases highlight the possibility that the distal region of 15q contains another gene regulating human growth, with LRRK1 being a potential candidate.

Detection of mutually exclusive mosaicism in a girl with genotype-phenotype discrepancies

Discordance between clinical phenotype and genotype has multiple causes, including mosaicism. Phenotypes can be modified due to tissue distribution, or the presence of multiple abnormal cell lines with different genomic contributions. We have studied a 20-month-old female whose main phenotypes were failure to thrive, developmental delay, and patchy skin pigmentation. Initial chromosome and SNP microarray analysis of her blood revealed a non-mosaic ∼24 Mb duplication of 15q25.1q26.3 resulting from the unbalanced translocation of terminal 15q to the short arm of chromosome 15. The most common feature associated with distal trisomy 15q is prenatal and postnatal overgrowth, which was not consistent with this patient's phenotype. The phenotypic discordance, in combination with the patchy skin pigmentation, suggested the presence of mosaicism. Further analysis of skin biopsies from both hyper- and hypopigmented regions confirmed the presence of an additional cell line with the short arm of chromosome X deleted and replaced by the entire long arm of chromosome 15. The Xp deletion, consistent with a variant Turner Syndrome diagnosis, better explained the patient's phenotype. Parental studies revealed that the alterations in both cell lines were de novo and the duplicated distal 15q and the deleted Xp were from different parental origins, suggesting a mitotic event. The possible mechanism for the occurrence of two mutually exclusive structural rearrangements with both involving the long arm of chromosome 15 is discussed.

Chromosomal imbalance letter: Phenotypic consequences of combined deletion 8pter and duplication 15qter

Exact breakpoint determination by oligonucleotide array-CGH has improved the analysis of genotype-phenotype correlations in cases with chromosome aberrations allowing a more accurate definition of relevant genes, particularly their isolated or combined impact on the phenotype in an unbalanced state. Chromosomal imbalances have been identified as one of the major causes of mental retardation and/or malformation syndromes and they are observed in ~2-5% of the cases. Here we report a female child born to non-consanguineous parents and having multiple congenital anomalies such as atrial septal defect and multiple ventricular septal defects, convergent strabismus, micropthalmia, seizures and mental retardation, with her head circumference and stature normal for her age. Cytogenetic study suggested 46,XX,add(8)(p23). Further analysis by array-CGH using 44K oligonucleotide probe confirmed deletion on 8p23.3p23.1 of 7.1 Mb and duplication involving 15q23q26.3 of 30 Mb size leading to 46,XX,der(8)t(8;15)(p23.3;q23)pat.arr 8p23.3p23.1(191,530-7,303,237)x1,15q23q26.3(72,338,961-102,35,195)x3. The unique phenotypic presentation in our case may have resulted from either loss or gain of a series of contiguous genes which may have resulted in a direct phenotypic effect and/or caused a genetic regulatory disturbance. Double segmental aberrations may have conferred phenotypic variability, as in our case, making it difficult to predict the characteristics that evolved as a result of the global gene imbalance, caused by the concomitant deletion and duplication.