Clinical spectrum of neural tube defects with special reference to karyotyping study.

BACKGROUND: Neural tube defects are common congenital malformations of the central nervous system. Despite years of intensive epidemiological, clinical, and experimental research, the exact etiology of NTD remains rather complex and poorly understood. The present study attempted to look into the association of occurrence of NTD with reference to folic acid levels, along with karyotyping status.
MATERIALS AND METHODS: Detailed history was taken with emphasis on age of the baby and mother, parity, antenatal folic acid intake. Five milliliters of blood was drawn from all the babies and their mothers and divided equally in preheparinized vials (for karyotyping) and plain vials (for folic acid estimation). The total duration was 2 years.
RESULTS: The total number (n) in the study group was 75. The folic acid level was less in affected babies and their mother when compared to matched controls. Chromosomal defect was observed in nine of the 75 patients. Karyotyping defects were higher in children born to mothers of the age group 31-40 years and when their birth order was second.
CONCLUSION: Folic acid supplementation needs to be continued to prevent the occurrence of NTD, and the perinatal identification of NTD should alert one to the possibility of chromosomal abnormalities and prompt a thorough cytogenetic investigation and genetic counseling.

Introduction

Neural tube defects are common congenital malformations of the central nervous system. It arises from the neural tube, which either fails to close properly or becomes over distended and ruptures after initial normal closure.[1-3] Neural tube defects have an incidence of 1-2/1000 births.[45] The development of neural tube is a multistep process, which is strictly controlled by genes and modulated by a host of environmental factors. It involves gene–gene, gene–environment, and gene–nutrient interactions. Despite years of intensive epidemiological, clinical, and experimental research, the exact etiology of NTD remains rather complex and poorly understood.[6] It has been linked to the deficiency of folic acid in the pregnant ladies.[3]

The present study attempted to look into the association of occurrence of NTD with reference to folic acid levels, along with karyotyping status.

Materials and Methods

The present study was conducted in Department of Pediatric Surgery of the University hospital, in collaboration with the Centre for Experimental Medicine and Surgery from August 2009 to July 2011. It was a prospective (pilot) study, which was approved by the hospital ethical and postgraduate committee. The study group comprised patients with NTD and their mothers attending OPD/admitted. The control group comprised 50 babies that did not have any congenital malformation or major illness.

Detailed history was taken with emphasis on age of the baby and mother, parity, antenatal folic acid intake. The baby was examined to determine the type of defect, its site, neurological deficit (club foot, paraparesis/paraplegia, patulous anus). The ultrasonography (USG) of cranium was performed in all patients and computed tomography was done in selected patients to evaluate for hydrocephalus.

Five milliliters of blood was drawn from all the babies and their mothers and divided equally in preheparinized vials (for karyotyping) and plain vials (for folic acid estimation). Folic acid estimation was done by the enzyme linked immunosorbent assay (ELISA) method. The data were entered into the Excel sheet and analyzed using SPSS 16.0 version for Windows. The statistical analysis was done using a chi-square test and Fisher's exact test. A P-value of ≤0.05 was considered significant and the values were expressed as mean ± SD.

Results

The total duration was 2 years. The total number (n) in the study group was 75. The male to female ratio was 2:1. Sixty-seven (89.3%) patients presented within 6 months of age. Open neural tube defect was present in 49 (65.3%) patients. Rest 26 (34.7%) had closed defect. The dorsolumbar region was the most common affected site (43 cases, 57.3%), followed by the lumbosacral region.

It was observed that more number of affected children were born to mothers of age group 31-40 years. In our study, second-order child (46.6%) was observed to be more commonly affected by NTDs [Table 1].

Table 1

Parity of the mother of NTD affected child (n = 75)

The folic acid level was less in affected babies and their mother when compared to matched control. The mean FA values in NTD babies and their mothers were 22.5 and 22.0 ng/ dl and in their matched controls were 24.0 and 23.0 ng/ dl respectively; however, the difference was not statistically significant [Table 2].

Table 2

Folic acid estimation in the control and cases

Chromosomal defect was observed in nine of the 75 patients. Of these, five had numerical (10%) and four (8%) had structural abnormality. Karyotyping done on mothers revealed chromosomal defects in nine of them. Of these, three (6%) had numerical and six (12%) had structural aberration. Karyotping defect was higher in children born to mothers of the age group 31-40 years and when their birth order was second. Karyotyping defects were higher in mothers of the age group 31-40 years and also in a subgroup of those having second-order affected child. The difference was, however, statistically insignificant [Table 3].

Table 3

Karyotyping defects in the two groups

Discussion

Several observational studies have concluded reduced risk for NTDs in women who took supplements containing FA or had higher dietary intake during early pregnancy.[78] In most of these studies, there has been no direct estimation of the serum folic acid level. One such study has been previously carried out in our department, and had shown a significant difference of serum folic acid in cases and controls of both supplemented and nonsupplemented group.[9] In continuation of the earlier study, we have again estimated the serum folic acid level and found it to be consistently low in NTD babies and their mothers, compared to the controls.

The etiology of NTD is now regarded to be multifactorial and genetic component is increasingly being considered. We had performed karyotyping in 75 patients and found aberrations in nine babies and nine mothers. Chromosomal defect was also noticed in one of the controls used for babies, and was regarded incidental.

The karyotyping defects observed in our study were in the form of partial aneuploidy leading to structural aberration. Also, aneuploidy in the form of monosomy and trisomy of the genome was observed. Hume et al.[10] reported 53 pregnancies affected by NTD and found that 13.2% of the fetuses had abnormal chromosomes, thereby suggesting that fetal karyotyping is essential to evaluate fetuses with NTDs. Others have also noticed such chromosomal abnormalities.[1112]

Neural tube defects are one of the common congenital malformations in our hospital. Though NTD is multifactorial in origin, still few etiological factors are important. Higher age of mother and the second child onward the incidence of the disease is more. The low level of folic acid both in mother and affected babies highlights the importance of folic acid supplementation to prevent such occurrence in the family.

It can be argued that the occurrence of chromosomal abnormalities was not statistically insignificant; hence, it may not be needed. However, this was a pilot study and the sample size was small. A larger sample size may show significant results. Still, aberration of karyotyping noticed in newborn and their mothers cannot be overlooked as the causative agent for the genesis of the malformation.

To conclude, folic acid supplementation needs to be continued to prevent the occurrence of NTD, and the perinatal identification of NTD should alert one to the possibility of chromosomal abnormalities and prompt a thorough cytogenetic investigation and genetic counseling.