Response to Comments Received on our Published Article “An Observational Case-control Study for BDNF Val66Met Polymorphism and Serum BDNF in Patients with Major Depressive Disorder (MDD)”

Dear Commentators,

Thank you for your interest in engaging with our published study. ¹ The study aimed to examine the Brain Derived Neurotropic Factor (BDNF) Val66Met polymorphism and serum levels in patients with major depression and healthy controls (HC). The aim was admittedly stated in broad terms; however, it was operationalized adequately with Tables 1–4 ¹ and corresponding analyses aligning with the stated aim. Given the limited Indian data, we intended to primarily focus on group differences between cases and controls concerning BDNF polymorphism (and serum levels). Although bivariate analyses were briefly included to explore associations, they did not yield statistically significant or clinically meaningful findings (Table 5). ¹ Multivariable regression may have offered additional insights, but it was not a focus for the current article. HCs were biologically unrelated attendants or friends accompanying patients to the outpatient department. They were screened using a semi-structured clinical interview to exclude any psychiatric illness in themselves or their biological relatives. The clinician-administered Hamilton Rating Scale for Depression (HAM-D) and self-rated Clinically Useful Depression Outcome Scale (CUDOS) tools were included to assess illness severity and functioning aspects comprehensively. As correctly noted, the study did not assess treatment response, which is better evaluated prospectively; these scales were included to understand the profile better and characterize the sample (Table 1). ¹ Due to its high prevalence in the general population, ² nicotine use was not excluded for pragmatic considerations.

As shown in Table 1, ¹ age and gender were comparable across groups. Body mass index (BMI) was higher among cases, possibly due to illness or medication effects, and was acknowledged as a potential confounder. Other factors, such as physical activity and lifestyle, were not assessed and are noted as limitations. The number of depressive episodes is shown in Table 1. ¹ Additionally, available symptom data is being provided here: 65.5% reported death wishes, 29.9% had suicidal ideation with a specific plan, 13.8% had attempted suicide, and 9.2% reported psychotic symptoms in the current episode. No patient had active suicidal risk or psychotic symptoms at enrollment. The observation of relatively lower BDNF levels in cases and controls is quite valid. However, the values were comparable to some other Indian studies on depression, such as Jeenger et al. (2018) ³ and Gupta et al. (2016), ⁴ which observed similar absolute levels in their samples. However, the values are higher in some other studies from India.^5,6 The BDNF levels have varied widely in the literature, which might be due to differences in assay type, sampling timing and handling, population, and treatment characteristics. ⁷ The cross-study comparisons can be better made within the context of similar methodological protocols. All samples in our study were stored at –20 °C, processed in a single batch, and subjected to a single freeze-thaw cycle before analysis using an Enzyme-linked immunosorbent assay (ELISA) kit (BIOCODON, Kansas, USA). Although not detailed in the article, BDNF levels in medicated cases versus controls showed findings similar to those observed in the overall case-control comparison.

The grouping of Val66Met polymorphisms in results follows a standard approach, where the dominant model compares Met carriers with Val/Val, assuming only one Met allele may affect risk. The recessive model contrasts Met/Met with all others, while the over-dominant model tests whether Val/Met differs from both homozygous groups. As noted, Table 5 ¹ presents the bivariate analysis of key variables in relation to BDNF polymorphism and serum levels. This was presented in a condensed format due to space constraints and because it was not the article’s primary aim. Statistical tests and footnotes are provided for accurate interpretation. The non-significant findings for all clinical variables were not tabulated, but mentioned in the narrative results.

Last, the discussion on case-control versus cross-sectional design is respectfully noted. Since genetic polymorphisms are innate and precede illness onset, a case-control design was deemed to be appropriate for our study. However, serum BDNF levels are state-dependent, but were included as a secondary biological measure alongside polymorphism. That said, we acknowledge that the distinction between case-control and cross-sectional designs can be debatable for studies with both genetic and state-dependent variables.

Final, we thank the authors for highlighting specific strengths of our study’s methodology and the relevance of its findings, and for contributing to discussions that may inform future research.