How Do Sickle Cell Genes Protect Tribal People from Deadly Malaria? Is This a Type of Natural Selection?

Special Article - Anaemia

Ann Hematol Onco. 2023; 10(5): 1437.

How Do Sickle Cell Genes Protect Tribal People from Deadly Malaria? Is This a Type of Natural Selection?

Shanti Lal Choubisa*

Department of Advanced Science and Technology, National Institute of Medical Science and Research, NIMS University Rajasthan, Jaipur, Rajasthan 303121, India; Former Department of Zoology, Government Meera Girls College, Udaipur, Rajasthan 313002, India

*Corresponding author: Shanti Lal Choubisa Department of Advanced Science and Technology, National Institute of Medical Science and Research, NIMS University Rajasthan, Jaipur, Rajasthan 303121, Indial; Department of Zoology, Government Meera Girls College, Udaipur, Rajasthan 313002, India. Email: [email protected]

Received: July 28, 2023 Accepted: August 30, 2023 Published: September 14, 2023

Abstract

In humans, genetic mutations have led to the formation of several haemoglobin (Hb) variants during human evolution. These mutations usually occur in the genes for a and Β- polypeptide or globin chains of haemoglobin located on chromosomes 11 and 16, respectively. Among these haemoglobin variants, sickle cell haemoglobin (Hb-S) is highly significant in the humans. In fact, this abnormal or mutant haemoglobin is the resultant of a point mutation in the gene for Β-globin, located on chromosome 11. No doubt, this sickle cell gene is relatively more prevalent among tribal people and widely distributed in those geographic regions where the dreaded Plasmodium falciparum-malaria is hyperendemic. In the human population, this mutant gene exists in two forms, the heterozygous (Hb-AS) and homozygous (Hb-SS) states. But this sickle cell gene is also found in association with other mutant genes of erythrocyte or red cell genetic disorders, such as abnormal Hb-C, Β-thalassemia, G-6-PD enzyme deficiency, etc.

It is well known that tribal people generally live in forest ecosystem where dreaded malaria is also found to be endemic. How have these tribal people been able to protect themselves from this dreaded malaria for thousands of years in such a hostile environment, when they were most likely to be infected with the malaria parasite? Actually, its secret is hidden in these sickle cell genes only. Tribal individuals who have these genes in the heterozygous state (Hb-AS) do not get malaria or are protected from malaria and lead a healthy life. Several studies have confirmed that AS heterozygote people are protected against malaria. In contrast, those who have these genes in the homozygous (Hb-SS) state (homozygotes) develop sickle cell anaemia, which is fatal. Such patients die early due to severe malaria i.e AS heterozygotee individuals have a double advantages. In fact, it is a type of natural selection and also shows a balanced polymorphism in tribal people which is based on Darwin’s theory. This current communication provides factual and scientific information about the origin of sickle cell genes in the context of natural selection and how these genes protect tribal individuals from malaria. This communication is useful and important for zoologists, scientists working on human evolution, and medical scientists.

Keywords: Alleles; Erythrocytes; Haemoglobin; Homozygotes; Heterozygotes; Malaria; Natural selection; Sickle cell gene; Sickle cell haemoglobin; Sickle cell anaemia; Sickle cell trait; Tribals

Introduction

Except perhaps Africa, India has the largest population of tribal people in the world. In a way, these people are also called the children of nature and their lifestyle is determined and molded by the ecosystem. There are over 533 tribes in India that live in diverse forest ecosystems. As per 2011 census, 10.42 Cr. Indians notified as 'Scheduled Tribes' (ST) constitute 8.6% of the total population in the country. In 2001, the tribal population of India increased to 10.43 million from 8.43 Cr. In the world, among diverse ethnic groups or tribes, many tribes are still primitive types that still survive in hostile environments where malaria is more prevalent and highly endemic. It is well known that malaria is fatal, which is caused by infection with Plasmodium falciparum-malaria parasite. According to the recent World Malaria Report, 2022, by World Health Organization [1], thousands of people die due to malaria worldwide every year in malaria endemic countries. Interestingly, the malaria parasite and its vectors and the tribal people have been living together for thousands of years or centuries and are still living together, yet the tribal people are still alive and protected from malaria infection. After all, how do these tribal people escape from malaria and stay safe? In fact in these tribal people it has been possible by natural selection. Probably this is a wonderful, unique and rare example in human biological development or evolution.

In fact, malaria itself is an important biological factor responsible for this natural selection [2,3]. During biological evolution, this malarial strain or pressure caused a mutation in the Β-polypeptide or globin gene on chromosome 11 associated with human red blood cells (erythrocytes), leading to the formation of sickle cell haemoglobin (Hb-S) in these cells [4]. Because of this, the shape of the blood cells becomes sickle (Figure 1). These mutated Β- globin genes are also known as sickle genes, which inherited from one generation of tribals to another, which are still present in them. These sickle genes are responsible and capable of protecting these tribals from deadly malaria [5-21]. In addition to the sickle cell gene, some other genes for red cell genetic disorders, such as Hb-C, Β-thalassaemia, glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, and blood groups are also found for genetic resistance to malaria in human populations [22-36]. This current communication provides factual and scientific information about the origin of sickle cell genes in the context of natural selection and how these genes protect tribal individuals from malaria. This communication is useful and important to zoologists, scientists working on human evolution, and medical scientists.

Citation: Choubisa SL. How Do Sickle Cell Genes Protect Tribal People from Deadly Malaria? Is This a Type of Natural Selection?. Ann Hematol Onco. 2023; 10(5): 1437.