Prenatal detection of distal 1q21.1q21.2 microduplication with abnormal ultrasound findings

Abstract Rationale: 1q21.1 duplication is an uncommon chromosomal submicroscopic imbalance which is associated with growth/mental retardation, dysmorphic features, autism, multiple congenital and neuropsychiatric disorders. Patient concerns: Two pregnant women underwent amniocentesis for cytogenetic analysis and chromosomal microarray analysis (CMA) following abnormal ultrasound findings. Case 1 presented short nasal bone and case 2 showed absent nasal bone, ventricular septal defect and umbilical cord circling in ultrasonic examination. Diagnoses: G-banding analysis showed that the two fetuses presented normal karyotypic results while CMA detected 1.796 Mb (case 1) and 1.242 Mb (case 2) microduplications in the region of 1q21.1q21.2 separately. Furthermore, the CMA also revealed a 1.2 Mb microdeletion of 8p23.3 in case 1. Interventions: The couple in case 1 chose to terminate the pregnancy, while the couple in case 2 continued the pregnancy and finally delivered a male infant who presented low nasal bridge and ventricular septal defect. Outcomes: The 1q21.1q21.2 duplications in our report were located in the distal 1q21.1 region, overlapping with 1q21.1 duplication syndrome. Case 2 was the first reported live birth with 1q21.1 duplication according to prenatal CMA detection in China. Lessons: The genotype-phenotype of 1q21.1 duplication is complicated due to the phenotypic diversity, incomplete penetrance, and lack of obvious characteristics. So it is difficult to predict the postnatal development and health conditions clinically. Hence, long term follow up is necessary for newborn infants with 1q21.1 duplication, irrespective of whether the duplication is de novo or inherited.


Introduction
Chromosomal microdeletions and microduplications, making up a fraction of copy-number variants (CNVs), have long been associated with mental retardation, congenital abnormalities, autistic disorders and other genetic disorders. As molecular techniques with high resolution, chromosomal microarray analysis (CMA) play a critical role in detecting these chromosomal submicroscopic imbalances, which are too small to be identified through conventional karyotype analysis. [1] The deleted/duplicated size, locus and dosage-sensitive genes involved have close correlation with the abnormal manifestations in clinic. [2,3] Common CNVs associated with fetal anomalies include 22q11.21, 17q12, 16p13.11, 1q21.1, 15q13.3, and 10q21.1. [4] Chromosomal 1q21.1 microdeletions/duplications are rare aberrations of chromosome 1. Patients with CNVs in 1q21.1 locus share similar phenotypes with 22q11.2 deletion syndrome, and they usually exhibit variable features, characterized by congenital abnormalities, intellectual disability, dysmorphic features, schizophrenia, autism and normal phenotypes. [2,[5][6][7] Currently, it is difficult to assess the pathogenicity and clinic significance for cases carrying 1q21.1 microdeletions/ duplications.
For prenatal samples presenting karyotypic results, subchromosomal gains and losses of clinic significance can be detected in approximately 1% of structurally normal pregnancies and 6% with structural malformations. [1] Herein, we present two cases of prenatal diagnostic 1q21.1 microduplication exhibiting abnormal ultrasound findings. We also present a review on the clinical data involving similar 1q21.1 microduplication, and delineated the genotype-phenotype correlations.

Methods
Our study protocol was approved by the Ethics Committee of the First Hospital of Jilin University (No.2019-281), and the written informed consents were obtained from the couples for publication of this case report and accompanying images.

Cytogenetic analysis
Chromosomal karyotypic analysis with a resolution of 300 to 400 bands was performed on G-band metaphases prepared from cultured aminotic fluid cells and peripheral blood cells according to standard protocols in our laboratory. Twenty metaphases were analyzed for all samples. The International System for Human Cytogenetic Nomenclature nomenclature was used to describe all karyotypes. [8]

Case 1
A 23-year-old, gravida 1, para 0, pregnant woman underwent ultrasound examination at 25 weeks of gestation, which indicated a short nasal bone in the fetus. Subsequently, the woman underwent amniocentesis for cytogenetic analysis and CMA detection. G-banding analysis showed that the karyotype of the fetus was 46, XY, but CMA revealed a 1.796Mb duplication in the region of 1q21.1q21.2 and a 1.2 Mb microdeletion in the region of 8p23.3. Meanwhile, the couple also accepted karyotypic analysis. The husband's karyotype was 46, XY, t (1;5)(q25;q33) while the wife's was 47, XXX. Finally, the couple chose to terminate the pregnancy according to genetic counseling based upon abnormal CMA results.

Case 2
A 29-year-old, gravida 2, para 0, abortus 1, pregnant woman underwent ultrasound examination at 23 weeks of gestation, which showed absent nasal bone, ventricular septal defect and umbilical cord circling in the fetus. Afterwards, the woman underwent amniocentesis for cytogenetic analysis and CMA detection. The karyotype of the fetus was identified as 46, XY. However, CMA detected a 1.242 Mb duplication in the region of 1q21.1 q21.2. In order to identify whether the 1q21.1 microduplication of the fetus was de novo or parentally inherited, the couple accepted CMA after informed consent. It turned out that case 2 inherited the 1q12.1 microduplication from the father with normal phenotype. Based upon genetic counseling, the couple continued the pregnancy and delivered a male infant at 41 weeks gestation, whose birth weight was 3,700 g and length was 51 cm. We followed-up on the postnatal health conditions. The infant presented low nasal bridge and ventricular septal defect, and no other apparent abnormalities were observed till now.
In our study, the couples were nonconsanguineous and healthy. There was no family history of diabetes mellitus or congenital malformations in the couples. These couples denied any exposure to alcohol, teratogenic agents, irradiation, or infectious diseases during this pregnancy.

Discussion
In our study, we report two prenatal cases with 1q21.1 duplication accompanied by abnormal ultrasound findings. Case 1 presented short nasal bone, with a 1.796 Mb microduplication of 1q21.1q21.2 and a 1.2 Mb microdeletion in 8p23.3. Case 2 showed absent nasal bone and ventricular septal defect, with a 1.242 Mb microduplication of 1q21.1q21.2. The duplicated regions in both cases overlapped with 1q21.1 duplication syndrome. To our knowledge, case 2 was the first live birth with 1q21.1 duplication according to prenatal CMA detection in China.
Genetic disorders related to mental retardation, congenital abnormalities, autism or other clinic phenotypes could result from the alternation of gene dosage owing to chromosomal gains or losses. [21] According to the DECIPHER database, a total of 11 OMIM genes exist in the region of 1q21.1q21.2, two of which are morbid genes with clinical diseases (Table 2). According to the ClinGen database, there is no available pathogenic evidence for triplosensitivity associated with the genes involved. Based upon the functions and implications, we delineated the potentially pathogenic genes which might explain the observed abnormalities and predict the possible phenotypes in future.
GJA5 (OMIM: 121013), containing three exons, encodes a gap junction protein connexin 40 which is expressed in the right ventricular outflow tract. [22] It plays critical roles in cell adhesion, intercellular communication and heart development. [13] GJA5 was regarded as a candidate gene which was implicated in the etiology of cardiovascular diseases in patients carrying chromosomal 1q21.1 duplication/deletion. Duplications and mutations of GJA5 were associated with Tetralogy of Fallot (TOF). [23,24] Soemedi et al [25] observed that duplication of GJA5 alone is associated with an 10-fold increase in the risk of TOF. In addition, mutations of GJA5 were also detected in patients with arrhythmias. [23] And dosage alterations of GJA5 might be responsible for cardiomyopathy. [15] As the flanking gene of GJA5, the abnormal expression of GJA8 (OMIM: 600897) has also been correlated with congenital heart disease (CHD). [14,15,25] In addition, GJA8 was associated with eye abnormalities and schizophrenia. [9,26] We speculated that the duplications of GJA5 and GJA8 might be responsible for the occurrence of ventricular septal defect in case 2. High expression of CHD1L can be observed in different brain regions, especially in the cerebellum. [16,19] Dou et al [12] assumed that CHD1L can promote neuronal differentiation in human embryonic cells and affect nervous system development. In addition, overexpression of CHD1L was closely associated with patients with TOF, double outlet right ventricle, and pulmonary artery stenosis. [27] Besides, CHD1L might also be implicated in autism spectrum disorder, attention deficit hyperactivity disorder and language dysfunction. [17] PRKAB2 (OMIM: 602741) encodes the b2-subunit of AMPactivated protein kinase (AMPK), which is a serine/threonine protein kinase activated by various cellular stimuli. It is highly expressed in cardiac muscle and plays critical roles in brain function and energy metabolism. [5,28] Moreover, PRKAB2 might have close association with schizophrenia. [17] Since research on other genes in this 1q21.1 region are scarce, their potential functions and effects remain to be further investigated.
In addition, the CMA also detected a 1.2 Mb deletion in 8p23, which contained two critical genes: FBXO25 (OMIM: 609098) and DLGAP2 (OMIM: 605438). According to the ClinGen database, there are no available pathogenic evidence for haploinsufficiency associated with the two genes till now.
High diversity inter-and intrafamilial outcomes have been discovered among the members sharing the same 1q21.1 duplication, ranging from normal phenotypes to severe anomalies. [12] The occurrence of a parent carrying 1q21.1 duplication without evident phenotypes makes it intractable to assess the clinic significance for offsprings with the same chromosomal duplication. [7] In our study, case 2 inherited 1q21.1q21.2 duplication from his normally phenotypic father. The child presented low nasal bridge and ventricular septal defect, however, regular psychiatric, neurocognitive, motor skill, and neurologic status should be followed up and assessed. For the parents of case 1, since both of them presented with chromosomal abnormalities, preimplantation genetic diagnosis would be an appropriate choice if they intend to conceive again.
In this study, we delineated the clinic phenotypes and molecular cytogenetic findings of two prenatal cases carrying 1q21.1q21.2 microduplication. Our study not only enriches genotype-phenotype of 1q21.1 duplication in clinical setting, but also offers a better understanding for such chromosomal gains in prenatal diagnosis. Genetic counseling should be offered by clinicians based upon full consideration of phenotypic diversity, incomplete penetrance, and diverse phenotypic spectrum. And long term follows up involving postnatal development and clinical presentations should be assessed till adulthood, irrespective of whether the 1q12.1 duplication is de novo or inherited.