|Year : 2020 | Volume
| Issue : 6 | Page : 677-680
Maternal 2:18 chromosomal translocation manifesting as cause for developmental delay in a proband
Purushottam Rao Manvikar, Preeti Awari
Department of Anatomy, Dr. DY Patil Medical College, Hospital and Research Centre, Dr. DY Patil Vidyapeeth, Pune, Maharashtra, India
|Date of Submission||03-Oct-2019|
|Date of Decision||03-Apr-2020|
|Date of Acceptance||25-Jun-2020|
|Date of Web Publication||6-Nov-2020|
Purushottam Rao Manvikar
Department of Anatomy, Dr. DY Patil Medical College, Hospital and Research Centre, Dr. DY Patil Vidyapeeth, Pimpri, Pune, Maharashtra
Source of Support: None, Conflict of Interest: None
Developmental disabilities are a group of related chronic disorders of early onset and said to affect 5% to 10% children. Mental Retardation or intellectual disability has been redefined and replaced with Global developmental delay by WHO as the parameters of diagnosis of such a condition become valid and reliable by the age of five years of the proband. In Indian context the incidence is 2.5%.Chromosomal aberrations either structural or numerical account for 25-30% in general population. Chromosomal analysis and karyotyping is considered as primary investigation in management protocols of such children. Authors present a case of six months old child referred to cytogenetic laboratory with a clinical suspicion of delayed mile stone. Proband was born to a non-consanguineous couple delivered by lower segment caesarian section (LSCS) with no untoward incidents during intraoperative and post-operative phase of surgery. There was history of earlier fetal loss at third month of gestation due to cardiac defects diagnosed prenatally. Karyotyping of proband revealed 2:18 translocation. Karyotype of parents was done to find out the source of translocated chromosome. It was revealed that 2:18 translocated chromosome was seen in karyotype of mother of proband. Karyotype of proband was reported as 46,XX; der(18) t(2:18)(q31q35 ;q21q22)mat As per ISCN guidelines. Case has been reported for the rarity of such an occurrence.
Keywords: Developmental delay, intellectual disability, mental retardation, translocation
|How to cite this article:|
Manvikar PR, Awari P. Maternal 2:18 chromosomal translocation manifesting as cause for developmental delay in a proband. Med J DY Patil Vidyapeeth 2020;13:677-80
|How to cite this URL:|
Manvikar PR, Awari P. Maternal 2:18 chromosomal translocation manifesting as cause for developmental delay in a proband. Med J DY Patil Vidyapeeth [serial online] 2020 [cited 2020 Nov 26];13:677-80. Available from: https://www.mjdrdypv.org/text.asp?2020/13/6/677/300140
| Introduction|| |
Developmental disabilities are a group of related chronic disorders of early onset and said to affect 5%–10% of children. These disabilities once categorized under intellectual disabilities could be diagnosed by the time the child reaches the age of 5 years when standard measures of intelligence become reliable and valid. Term mental retardation (MR) which was in vogue is merged with intellectual disability now replaced by global developmental delay (GDD) which in turn is defined as the delay in attainment of developmental milestones at the expected age and is implied by deficits in learning and adaptation.
The incidence of GDD is 1%–3%.,, As per the World Health Organization, the worldwide incidence of the same is about 5% in children <14 years of age. In Indian children, below 2 years of age, the number is 2.5%. Chromosomal abnormality, either numerical or structural, is one of the etiological factors for GDD. The incidence reported is 25%–30% in the general population.,
In view of the magnitude of this problem, the authors report the case of a 6-month-old child referred for karyotyping to the Cytogenetic Laboratory, Department of Anatomy, by the pediatricians of Dr. DY Patil Medical College, Hospital and Research Centre, Pune, with the provisional clinical diagnosis of developmental delay.
| Clinical History|| |
The proband was born to nonconsanguineous couple. However, there was uncle–niece consanguinity on the paternal side in grandparents [Figure 1]. Delivered by lower segment cesarean section at the 38th week of gestation, there was no event of fetal hypoxia, and the child cried immediately after birth. The Apgar score was 7/10 at 1 min and 9/10 at 5 min. The birth weight of the child was 2.7 kg. Exposure to teratogens of any sort and history of infection and major illness of mother during pregnancy were not found. However, there was one incidence of medical termination of pregnancy done at the 3rd month due to a cardiac anomaly in the fetus, which was detected by ultrasonography, but the details of the cardiac anomaly were not available. The child presented with dysmorphic face, epicanthal folds, and hypertelorism. Partial neck holding was present. After taking due consent from the parents as per protocol, karyotyping of the proband was done with conventional microculture and GTG banding of peripheral lymphocytes. Two milliliters of blood sample was collected in heparinized tubes, cultured, and lymphocytes were harvested. On chromosomal analysis, additional material on the long arm of chromosome 18 was detected in the proband. Metaphase spread count was increased to 100, and all the spreads showed additional chromosomal material at 18q. The rest of the chromosomes were normal and did not match with a clear translocation. To find the source of this additional material on chromosome 18 in the proband, karyotyping of the parents was undertaken. Karyotype of the father [Figure 2] was normal, i.e., 46XY. However, in mother, a balanced insertional translocation of part of the long arm of the chromosome 2 on chromosome 18 was observed. Mother's karyotype [Figure 3] was 46, XX;t(2:18) (q31q35;q21q22). This suggested that the abnormal chromosome in the child was the result of the transmission of structural rearrangement from the mother. The karyotype of the child [Figure 4] was 46;der(18) t(2:18)(q31q35;q21q22) mat. signifying that this additional genetic material is derived from the mother. This additional load of the genome on the chromosome 18 seemed to be the etiolgical factor for the developmental delay in the proband. Confirmation by fluorescent in situ hybridization was suggested, and the case was referred to the department of pediatrics for further management.
|Figure 4: Karyotype of the proband: 46,XX; der(18) t(2:18)(q31q35;q21q22)mat|
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| Discussion|| |
Genetic mutations can be duplication, deletion, or rearrangement of DNA. The changes in chromosome structure which are large enough to be detectable under the light microscope are called as chromosome aberrations. Structural abnormalities occur as a result of chromosomal breakage and abnormal reunion. Synapse between homologous regions of nonhomologous chromosomes may lead to accidental recombination between nonhomologous chromosomes, leading to translocation. The insertional translocations are less common. They may occur within a chromosome or between two chromosomes. The balanced carrier of such insertion translocations will be healthy, but the segregation of two translation derivatives during meiosis will lead to an unbalanced state in the proband with either deletion or duplication of inserted segment. Parents with balanced chromosomal translocations may deliver a live-born infant with varying degrees of developmental abnormality depending on the nature of the chromosomal imbalance.
Little experimental evidence exists on the meiotic behavior of insertional translocations, but a theoretical analysis shows that at least 26 possible segregants can result from the meiotic process. If the inserted fragment is large, a quadrivalent with a loop might be formed allowing complete pairing of the chromosomes involved in the rearrangement.,
Mechanism of translocation
In the present case, the quadrivalent which might have been formed in maternal gametogenesis is shown in [Figure 5]. Out of 26 different possibilities of segregation, the maternal gamete containing normal chromosome 2 and the derived chromosome 18 might have been fertilized by parental gamete [Figure 6], leading to the karyotype 46XX; der(18) t(2:18) (q31q35;q21q22) mat in the proband.
In carriers of balanced translocation, the possible reason for the association of congenital malformation could be gene inactivation or disruption at the breakpoint.
Rajasekhar et al. had reported various cases of developmental delay with translocation.
Usha Dave et al. have mentioned chromosomal translocations as the cause of MR in 5.7% of people in the Indian population.
To the best of our knowledge, this seems to be the first reported case of maternal 2:18 chromosomal translocation manifesting as delayed development in a proband.
Couples with genetic disorders including single gene defects, sex-linked conditions, or chromosome rearrangements face a reproductive risk. Preimplantation genetic diagnosis (PGD) is a diagnostic tool to avoid inheritance of chromosomal disease by transferring balancedin vitro fertilization (IVF) embryos and represents an alternative to prenatal diagnosis. IVF can increase the chance of conceiving and decrease the probability of miscarriages and chromosomally unbalanced offspring. The results of PGD chromosomal translocation carriers are comparable with regular IVF without PGD patients and allow a very significant reduction in the frequency of early pregnancy loss.
| Conclusion|| |
The chromosomal studies are mandatory in children with developmental delay. Karyotyping of parents becomes essential in cases of insertional translocations to find out the source of additional chromatin material. The deletions and duplications of the part of chromosome may lead to various abnormal phenotypic features, but the translocations are scarcely seen as the cause of the developmental delay. Translocation carriers may contribute to delayed milestones in their offsprings. Genetic counseling of the couple is needed to plan further course of management for such children. This case was presented because of unique maternal translocation between chromosomes 2 and 18 as a cause of delayed development because of its rarity.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]