The study cohort comprised schizophrenia patients with an average age of 35.56 ± 9.95 years, with females representing the majority (n = 54, 55.1%). A notable proportion of the schizophrenia patients reported a familial history of similar disease (33.3%), while a subset presented with concomitant chronic disease (24.3%). Comparative analysis of the digital ridge count, specifically on the second and fourth digit, revealed significant difference between schizophrenia and healthy volunteers. Furthermore, examination of fingerprint pattern highlighted a significant dispolarity solely in the fingerprint pattern observed on the left fourth digit between patients and healthy volunteers.
Schizophrenia, a prevalent mental illness often manifesting in adolescence or young adulthood, has been extensively studied for its age of onset, which serves to delineate distinct subtypes of the disorder. These subtypes represent unique variants with characteristic clinical profiles (Ahn, et al., 2016; Chen et al., 2018). Earlier-onset occurring before 18 years and extending to less than 40 years has been documented in various studies (Solmi et al., 2022; Altamura et al., 2014). The substantial proportion of patients are usually diagnosed by the age 40 years, and commencement of the disease before 45 years is a key feature in the DSM-III criteria for the disease diagnosis (Hyman, 2011; Girard and Simard 2008) Thus, the age of onset observed among our study participants aligns closely with the prevailing patterns reported in the literature, underscoring the consistency in the presentation of this defining characteristic across diverse cohorts.
The early age of onset of the disease plays a substantial role in expressing key defining disease features like; higher suicidality, more depressive symptoms, longer duration of untreated psychosis and poorer treatment outcomes (Diaz-Caneja et al., 2015; Joa et al., 2009). Additionally, early disease onset often correlates with specific clinical manifestations such as negative symptoms, increased disease severity, higher incidence of enuresis episodes, and more pronounced autistic traits (Coulon et al., 2020; Rammou et al., 2019). Although the current study did not assess the symptoms of recruited patients, it is reasonable to infer that their symptoms may not be as severe due to the absence of early onset disease. This inference aligns with the established association between early onset schizophrenia and the presence of more severe symptoms and clinical manifestations.
Various studies have presented conflicting perspectives on the role of gender in the manifestation and onset of schizophrenia. Some reports suggest that gender has no significant impact on the development of the disease, while others indicate a higher prevalence among males, particularly in cases of juvenile onset (male: female = 1.4:1) (Abel et al., 2010; Altamura et al., 2014) Conversely, older age onset disease appears to be more common among females, a phenomenon attributed to a potential protective effect of estrogen against excessive dopamine turnover (Riecher-Rossler et al., 2018; Li et al., 2016). Other hypotheses propose additional factors contributing to the gender disparity in age of onset. For instance, the presence of CC genotype within the transforming growth factor-β gene may promote early development of neuronal system and later age of onset of schizophrenia, specifically in females (Frydecka et al., 2015). Furthermore, initial misdiagnosis with affective disorders in females may inadvertently inflate the reported age of onset among females (Fernando et al., 2020). Additionally, males often exhibit a worse premorbid functional status and higher cannabis usage, which may influence age of onset based on gender (Neil et al., 2020). Thus, the older age of participants recruited in our study aligns with the predominance of females with schizophrenia in the case group, reflecting the delayed onset of illness typically observed in females compared to males.
Testosterone and estrogen play crucial roles in the embryonic development of the second and fourth digits, respectively, establishing their growth and development patterns. Once established during embryogenesis, these patterns remain relatively stable throughout subsequent development and into postnatal life (Han et al., 2020). This developmental phenomenon, governed by estrogen and testosterone, tends to exhibit greater consistency in the right hand compared to the left (Manning et al., 1998; Liu et al., 2012). Recent research has provided insight into the 2D:4D ratios of the left and right hands, with healthy men showing ratios of 0.958 ± 0.062 and 0.961 ± 0.062, respectively, and healthy women exhibiting ratios of 0.972 ± 0.048 and 0.970 ± 0.052, respectively (Han et al., 2020). These findings parallel the 2D:4D ratios observed in the current study, where healthy male volunteers demonstrated ratios of 0.96 ± 0.05 and 0.96 ± 0.04 for the right and left hands, respectively, and healthy female volunteers exhibited ratios of 0.97 ± 0.07 and 0.98 ± 0.05 for the right and left hands, respectively.
Efforts to assess the second to fourth digit ratio (2D:4D) have extended to specific sub-populations, including schizophrenia patients, with research revealing a distinct feminization of the ratio among Asian schizophrenia patients (Grimshaw et al., 1995; Jabeen et al. 2019). However, in our study, no feminization of the 2D:4D ratio was observed in schizophrenia patients when compared to healthy volunteers, even when stratified by gender. Nevertheless, within homogeneous sub-populations of schizophrenia patients of the same gender, females exhibited significantly higher 2D:4D ratios than males in both hands, indicating marked feminization of the ratio among female schizophrenia patients. This finding contrasts with previous studies that reported varied results such as: no difference in ratio, lower ratio among all patients, lower ratio among female patients, or higher ratio among all patients when compared to healthy volunteers (Mendrek et al., 2007; Hrabooszky & Hutson et al., 2002), The lack of consistency in findings challenges the practical utility of the 2D:4D ratio in diagnosing or screening for schizophrenia risk.
However, our results support the hypothesis of higher estrogen levels among females delays schizophrenia onset, evidenced by the significant impact on 2D:4D ratio in female schizophrenia patients compared to males. Furthermore, the similarity in the magnitude of the ratio between female patients and healthy volunteers, and vice versa, presents a challenge for using the 2D:4D ratio as a diagnostic tool, as they cannot be reliably distinguished in a population assessment.
In our study, a significant difference was observed in the proportion of loop (ulnar and radial) fingertip patterns on the left fourth finger between schizophrenia patients and healthy volunteers. Specifically, schizophrenia patients exhibited a higher proportion of loop patterns compared to healthy volunteers, and this was consistent with findings from earlier literature, indicating loop patterns as predominant among schizophrenia patients (Shakibaei et al., 2011; Singh et al., 1967). In addition, some studies have reported varying distributions of fingertip patterns among schizophrenia patients compared to healthy controls. For instance, some studies found arch patterns to be predominant in schizophrenia patients with the catatonic variant (Jhingan et al., 1989; Walther et al., 2019). While others reported lower proportions of arches and higher proportions of whorls among schizophrenia patients when compared to healthy controls (Bhusaraddi et al., 2019; Bhusaraddi et al., 2019). Further analysis based on gender revealed that male schizophrenia patients had an increased frequency of arch patterns and a decreased frequency of whorls when compared to females ( Shakibaei et al., 2011). Additionally, another study reported a higher proportion of whorl patterns among schizophrenia patients when compared to healthy volunteers (Norovsambuu et al., 2021). These findings underscore the variability in fingertip pattern distributions across different populations and studies, emphasizing the need for cautious interpretation of fingertip pattern association results.
Previous studies have provided insights into the average ridge count distribution among different fingers, indicating that the right and left thumbs typically exhibit the highest mean ridge count (Adamu et al., 2022). However, when assessing the mean ridge count across all ten fingers of schizophrenia patients and healthy volunteers, statistical analysis did not reveal significant differences (Norovsambuu et al., 2021). In our study, ridge counts were separately assessed for the radial and ulnar sides of the pulp region of the right and left second and fourth fingers in schizophrenia patients and healthy volunteers (Table 4). The statistical analysis demonstrated that the mean ridge count measurements for schizophrenia patients were significantly lower than those for healthy volunteers across all fingers, except for the radial ridge counts of the left second finger, which showed no significant difference (z = -1.76, p = 0.078). Despite this lack of significance, the ridge count for the left second finger in patients (9.19 ± 1.19) remained lower than that in healthy volunteers (9.55 ± 1.26). These findings align with trends observed in previous literature regarding total finger ridge count measurements when comparing schizophrenia patients to healthy volunteers (Golembo-Smith et al., 2012; Özyurt et al., 2010).. However, despite ridge count assessment performing relatively better than other quantitative anthropometric features in predicting schizophrenia disease risk, its diagnostic evaluation using the receiver operating curve paradigm categorically indicated that it remained a poor predictor of schizophrenia risk.