Dichromacy: Color Vision Impairment and Consanguinity in Heterogenous Population of Pakistan

Abstract

Abstract:
 Background and Objectives: Dichromacy, an X-linked recessive disorder is identified worldwide, more in males than females. In European Caucasians, its incidence is 8% in males and 0.5% in females. In India, it is 8.73% in males and 1.69% in females, and in Iran, it is 8.18% in males and 0.43% in females. Population based epidemiological data about dichromacy in different ethnic groups in Pakistan is not available. The aim of this study was to find out the population prevalence of inherited red-green dichromacy in a heterogenous population of the district of Chiniot, Punjab, Pakistan, and to determine the impact of consanguinity and ethnicity.
 Methods: In this cross-sectional study, boys and girls of the higher secondary schools were examined in the three tehsils of district Chiniot. Pseudoisochromatic Ishihara Test has been employed for detection of dichromacy in the study population. The sample size was calculated statistically as 260, which was expanded to 705 and divided by population density of the three tehsils.
 Results: Screening of 359 males and 346 females revealed 19 (5.29%) dichromat males and only 2 (0.58%) females. The study population belonged to 23 castes / isonym groups. The consanguinity found in the district of Chiniot is 84.82% and in the dichromat families, it is 85.71%, of which 52.37% are first cousin.
 Interpretation & Conclusion: The study has shown that the incidence of dichromacy could be reduced through genetic counseling

Attitudes towards genetic testing: The role of genetic literacy, motivated cognition, and socio-demographic characteristics

“…in Pakistan prevalence of consanguinity has been reported as high as 80% due to marriages within caste groups), which increases risk of genetic diseases (e.g. colour vision impairment [57] or β-thalassemia [58]). This may increase willingness to undergo genetic testing in these populations.…”

“…For example, there is evidence that genetic counselling can not only provide knowledge regarding a condition and potentially help to avoid a negative outcome (e.g. [57]) but also can improve perceived personal control and anxiety symptoms [94]. It is also worth noting that there was somewhat reduced variance for health-related concerns in the overall sample, as 90% of the sample answered "Yes" to one of the three questions that comprised this variable-"I would rather not know of any potential debilitating diseases in my future'.…”

X link color blind: A systematic review of congenital color vision deficiency cognitively and neurologically

“…Congenital color vision deficiency (CCVD) is a X-linked chromosomal deficiency that affects color differentiation, which results from abnormalities in genes coding for one or all three cone type photoreceptors [6][7]. Malfunctioning of cones is either due to the phototransduction cascade, or the alpha or beta sub-unit of the cyclic guanosince monophosphate gated cation channel [6,7].…”

“…Congenital color vision deficiency (CCVD) is a X-linked chromosomal deficiency that affects color differentiation, which results from abnormalities in genes coding for one or all three cone type photoreceptors [6][7]. Malfunctioning of cones is either due to the phototransduction cascade, or the alpha or beta sub-unit of the cyclic guanosince monophosphate gated cation channel [6,7]. The subclass of CCVD is divided based on the severity and what type of cones are affected: anomalous trichromacy and dichromacy involves damage in one cone type; monochromacy involves damage in two or more cone types [7].…”

“…Anomalous trichomacy is the most common type of color vision deficiency and is defined of having one cone type being not correctly aligned; patients with anomalous trichromancy may not have impaired colour vision, and amplification of the reduced color signal can allow anomalous trichromancy patients achieve relatively normalized color vision [5]. Compared to anomalous trichromacy, dichromacy involves lacking of one cone type, and patients with dichromacy are unable to see colors within this color range [6]. Monochromancy involves having one cone type or no cones at, leading to a complete loss of color perception.…”