It can be done broadly as follows -
- Defects affecting brain structure, such as anencephaly,encephalocele, and hydrocephalous.
- Defects affecting spinal cord structure, such as meningocele, myelomeningocele, and other forms of spina bifida.
Anencephaly is a condition of complete or partial absence of the brain; it is also known as exencephaly or craniorachischisis.This defect leads to fetal deaths, stillbirths, or neonatal deaths. In encephalocele, the brain and meninges herniate through a skull defect, especially in the occipital region.Hydrocephalous is characterized by the buildup of cavities deep within the brain that puts pressure and can cause brain damage. Spina bifida is characterized by the failure of fusion of the vertebral arches of the spine (Mikic et al., 2011). Meningocele is a condition in which the protrusion contains abnormal meninges and cerebrospinal fluid. In myelomeningocele, the cystic protrusion contains elements of the spinal cord and nerves (Santos et al., 2016). NTDs were reported to be high among children born to women of lower socioeconomic status (Welderufael et al., 2011).
ETIOLOGY OF NTDs
Neural tube defects (NTDs) are considered to be caused by heterogeneous factors. With many years of etiological assessment, it has been established that the variation in the frequency of spina bifida and anencephaly rely upon several demographic factors, and they are as follows – Habitat, Sex, Ethnic groups, Mother age, Family history, Social status, Congruity that can be partially genetic and partially exogenic (Nasri et al. 2014).
Environmental pollution and occupational hazards are the key contributors to many congenital anomalies and neurotoxicity. They result in many structural and functional alteration which results in different birth defects in the child. Such chemicals and radiations exposure during organogenesis can adversely affect the growing embryo and cause mutagenic effects leading to chromosomal abnormalities and syndromes (Huynh et al., 2021). It has been reported that trihalomethane in water has an interaction with folate related genes that can have more negative effects on women who are not taking folic acid supplements during their pregnancy and are at a high risk of NTDs in the child born to them (Sallman et al. 2020). It has been well established till date that periconceptional and early gestational use of 0.4 mg folic acid can approximately prevent 50% of NTDs. The socio-economic status and its association with Neural tube defects have been reported to be higher in the lower socio-economic class, which is predicted to be caused by vitamin deficiency and imbalanced dietary habits of a mother. Another possible cause for prevalence inthe lower socioeconomic class could be the occupational exposure of parents to different kinds of harmful chemicals and substances (Ladipo-Ajayi et al., 2020).
Exposure of mothers during pregnancy to the organic and inorganic solvents of pesticides can be a vital contributor to the child suffering from NTDs, and those parents who are associated with farm and farming activities are more prone to it. A statistically significant association of spina bifida with xylene and anencephaly with benzene and mercury exposure has been reported. Relatively more attention is to be paid to drinking water contamination concerning NTDs. It includes the mineral constitution, hardness, inorganic and organic constituent, water nitrates and other heavy metals, and chemical disinfection by-products(Dolk and Vrijheid 2003; Server, 1995).
Inorganic impurities of water whose relation with NTDs has been studied include heavy metals (lead, cadmium, arsenic, chromium, barium, mercury, selenium, and silver) and other elements such as nitrates, nitrites, fluoride. Water hardness (total calcium and magnesium) has been reported as a contributor in NTDs in different ecological studies whereas a high level of nitrates has implied anencephaly. Trihalomethanes (THM), i.e., Chloroform, bromoform and bromodichloromethane, and other chlorination byproduct have been associated with NTDs (Dolk and Vrijheid 2003; Costa et al. 2004).
Alcohol consumption, smoking, infection, and environmental pollution can be some other exogenous causing factors of NTDs. Environmental factors may play an essential role in the etiology of NTDs, which is considered to comprehend all non-genetic etiology, and it mainly includes mothers' age, illness, medications, uniformity, social class, and metabolic disorders (Blatter, 1994).
Generally, differences in sex exist in the ubiquity of NTDs, and more females are born than males with spina bifida (sex ratio 1/0.8), and for anencephaly, it extensively varies (sex ratio 1/0.45 to 1/1). Some studies suggest an association of NTDs with influenza infection, and women under the medications of analgesic and antidepressants are liable to have affected offspring. Maternal epilepsy and the use of antiepileptic drugs such as valproic acid increase the risk of spina bifida. In case of contraceptive use before pregnancy, some study suggests a child born with NTDs in case of women use drugs for ovulation induction (Wasserman et al. 1998; Sever, 1995).
This retrospective study aims to represent and analyzeNTD data-affected children and the prevalence of the types of NTDs in the Varanasi region.