Accounting for approximately 7% of the worldwide population as a carrier,
hemoglobin disorders referred to as 'hemoglobinopathies' are gradually attaining the position
of world's major health problems. These clinically heterogeneous group of inherited blood
disorders are associated with mutations in both alpha- and beta-globin genes, most common
being sickle cell anemia (trait and disease) and thalassemia. It is suggested that a minimum
of 3,00,000 children born each year are either affected by sickle cell anemia or one of its
variants or a form of thalassemia.
Till date more than 1000 disorders of hemoglobin synthesis
and/or their structure have been identified and characterised in a hope to generate genotype/
phenotype correlation that provides underpinnings of pathophysiological mechanisms of the diseases.
These disorders are fatal in the first few years of life burdening our concern for survival;
consciously redirecting us towards its diagnosis and treatment. In this unfortunate outcome linked
to genetic discrimination, Asians are unluckily attaining higher risk of hemoglobinopathies;
fueling our curiosity towards the knowledge of how's and why's of this irreversible issue that
escalates to new heights.
Let us update ourselves with the knowledge of disorders, their management and the genetic findings that
can help save an unborn's rightful life!
Hemoglobin (Hb) Overview
Hemoglobin (Hb) is a protein in red blood cells (RBCs), responsible for delivering oxygen from lungs to the
tissues and transporting carbon dioxide from the tissues back to the lungs; it is a most talked about tetramer
with heterodimers, composed of a pair of alpha-globin and beta-globin polypeptide chains. Major milestones of
Hb protein research involved genetie, physical, chemical and physiological approaches, that awakened the oxygen
transporter's function and connected the dots on its gene regulation besides the structural and functional
relationship of macromolecules. Be it Max Perutz's X-ray crystallography that deciphered the three dimensional
structure of Hb protein or Ernie Huehns's observation of different types of Hb expressed at different stages of
human development or identification of a wide range of globin gene mutants, the surge of progress in time widened
the horizon of clinical discoveries for Hb disorders, along with recent additions of molecular techniques for
prenatal diagnosis (PND) and polymorphism-based population studies that developed into an efficient and suitable
diagnostic tool. Out of all the findings in hemoglobinopathies inadequately expressed globin genes evoke the secret
of detailed working of globin heme protein family.
Family of globin heme proteins
As the central dogma of molecular biology states, genes are the indispensable source of information that
defines the specificity of a protein, our interest being the globin gene. Hemoglobin Al (HbA1), Hemoglobin
A2 (HbA2), Hemoglobin B (HbB), cytoglobin (CYGB), myoglobin (MB) and neuroglobin (NGB) are the types of
globin genes. There also is an Hemoglobin F (HbF), a highly expressed hemoglobin during the late fetal
gestation, whose expression gradually switches to HbA over several months. Hbf is known to delay the
symptomatic mutations which are present prenatally or at birth, masking the early detection of disorders,
if any.
An impressive degree of molecular studies have shed light on functionality of Hb, the multisubunit protein
and its capability to achieve optimal oxygen homeostasis. Oxygen. (without any chemical change to the oxygen
or the heme groups) is loaded onto Hb, transported and unloaded for metabolism; keeping iron in the heme group
in reduced state to maintain oxygen homeostasis. Globin chains, synthesised separately from alpha and beta gene
clusters located on human chromosomes 16 and 11, respectively coordinate with heme iron to stabilise it through
noncovalent interactions, and any mutations in the globin genes can lead to a range of impairments like hemoglobin
solubility forming intracellular polymers, developing amorphous precipitates, oxygen binding abnormalities
(erythrocytosis: high 0, affinity mutants, cyanosis: low 0, affinity mutants), structural alterations within
the heme pocket resulting in oxidation of heme iron or pseudocyanosis.'
Types of Hemoglobin disorders
Inherited disorders mainly fall into groups of thalassemia and structural Hb variants, and it is in our best
interest that we discuss these disorders, which are broadly categorised into,
1. Thalassemia syndrome
Absence or marked decrease in accumulation of the globin subunits of Hb characterises thalassemia: in alpha-
thalassemia absence or reduced production of alpha globin subunit, whereas absence or reduced production of
beta globin subunits result in betathalassemia. Thalassemia originated from Greek word thalassa1 - sea,
suggesting its origin to be the Mediterranean, however the condition spread to countries of the Middle East,
Transcaucasus, Central Asia, the Indian Subcontinent and Southeast Asia first. Asian Indians gave a rise in
characteristic haplotype mutations with the most common one being deletion of 619 bp (i.e. Betathalassemia),
allowing a feasible detection in prenatal diagnosis with DNA polymorphism analysis. Clinical overview of
thalassemia widely varies based on the severity and age when diagnosed, and depending on the extremities
patients receive mild to regular transfusion regimes, monitored chelation therapy, etc.
2. Sickle cell disorders
Glutamic acid when substituted with valine at the sixth residue of the beta-globin subunit results into sickle
hemoglobin (HbS), giving rise to the possibilities of homozygous or heterozygous conditions. In case of heterozygous
condition (sickle cell trait or HbAS) an individual is asymptomatic and only a severe hypoxia can manifest the sickle
cell trait, causing sickling, whereas in homozygous patients, Hbs undergoes polymerisation forming multistranded
fibers that create a gel and change
the shape of RBCs into elongated crescents, stripping off its oxygen carrying capacity. The severity of various
sickle cell syndromes varies greatly due to the concentration of Hbs in the red cell, developing severe chest pain,
fever, difficulty in breathing, also known to cause permanent damage to the brain, heart, kidneys, liver, spleen
and bones.
3. Unstable hemoglobin variants
Some substitutions that alter the solubility of Hb molecule and their tertiary/quaternary structure in the RBCs
results into unstable Hb precipitates: these precipitates are detected with the help of supravital staining that
form dark globular aggregates, namely Heinz bodies. RBCs end up having reduced life span in case of a Heniz body
hemolytie syndrome with varied severity. However, unstable Hb variants are a large group of Hb variants responsible
for red cell hemolysis in heterozygous carriers. The variants were classified into groups depending upon the amino acids brought about in specific structural sites such as subunit interfaces, heme contacts, central cavity, DPG
(diphosphoglycerate) binding site, C-terminus and internal/external residues. A definitive diagnosis for these Hb
variants requires either an analysis of globin structure or DNA sequencing.
Asians at a risk of Hb Disorders Southeast Asia consists of 10 countries with a total population of about 400 million and
accompanies a heterogeneous diversity in people with ethnic origins. Alpha-thalassemia (homozygous),
beta-thalassemia, Hb E, Hb constant spring (alpha-thalassemia of anemic patients in Myanmar) are highly prevalent
in Southeast Asians, different combinations of abnormal genes lead to over 60 different thalassemia syndromes,
making Southeast Asia one of the most complex thalassemia genotype locality. Thai, Khmer, Burmese, Malays,
Vietnamese and Bengalis are the groups having highest frequency of beta-chain mutations. Due to the major
molecular defects like point mutations, small deletions or insertions in the gene, patients have been affected
with fatal homozygosities or severe lifelong impaired heterozygosity
India and other developing Asian countries encounter difficulties in making the ends meet; also, factors like
social stigma, psychological block, expensive treatments, deprived education, etc. threaten the widespread
awareness, diagnosis and treatment of Hb disorders! Be it Thailand, Sri Lanka, Burma or Bangladesh, the threat
of hemoglobinopathies can be addressed by timely strategies for prevention and control, which includes population
screening for heterozygotes, genetic counselling and fetal diagnosis.
In India, marriages within the families is a traditional belief mainly done to keep the property in united form
within the family, this "Consanguinity is reported to be the highest in Asia (about 20% to over 50%) as an
indication of low socio-economic status, illiteracy and rural settlements. Consanguineous marriages brought
along genetic conditions inherited in an autosomal recessive manner) in the offsprings, placing an impending
risk on generations to come, like the threat of Hb mutations. Lack of medical infrastructure, good medical
facilities, genetic testing awareness, no government funding for healthcare and unmanageable population blocks
the Indians and their progeny with fatal genetic disorders. Mulled in ignorance and prejudice for a long time,
until the need for managing the abnormalities was looking right through the face, Indians focus on managing
hemoglobinopathies then shifted to following modalities such as:
- Blood transfusions - donated blood to the blood banks is tested for
malaria, syphilis, hepatitis B, HIV and Hepatitis C, keeping the transfusions infection free
- Chelation therapy - removes the excess iron in the body resulting from
repeated blood transfusions
- Wheat grass oil therapy - a research study that speculates reduction in blood transfusion requirement
- Using pharmacological agent -hydroxyurea - it induces fetal hemoglobin,
reducing ineffective erythropoiesis that alleviates symptoms of thalassemia intermedia and hematopoietic stem
cell transplanta
Hb Disorders Variants
Disorders and treatments, with it bring about innumerable fatalities and great expenses, and thus prevention
is a dire need considering the high frequency of these blood disorders looming over the Asian individuals.
In 1996, Iran initiated premarital screening and within 5 years 10,000 couples were screened for beta-thalassemia.
Astoundingly there was a 70% reduction in annual births of affected infants with betathalassemia major." This is
merely an example showing how tremendously preventive programs, education, premarital screening and prenatal
diagnosis reduces the burden of the disease on patients, families and the health services. India is in desperate
need for cost-effective treatments, awareness programs and preventive approaches, it thus becomes crucial
to address the following factors that will bring an impact, dwindling the risk of Hb disorders."
Genetic counselling
Since the time of Human Genome Project, genetic services have been rapidly increasing in type and complexity.
Prenatal hemoglobinopathy screening should ideally be a genetic screening service, however US could not pull
through with counselling the individuals showing positive test', thus it seems like a farfetched dream for
India, which focuses on
"sick care more than preventive care
Social aspect
Social and psychological aspects greatly affect Hb disorders and its management. The only effective way
to overcome the prevalence of Hb disorders is to make premarital screening compulsory and spread awareness
on Hb disorders and its lifelasting and life-altering effects! India is a land of diverse ethnicities and
beliefs, abortions, blood tied relations and marriage issues are hindrances difficult enough to fight the
prevalence!
Education
Mass media is an effective way to spread knowledge and awareness in public. Three
crucial aspects need to be covered while addressing hemoglobinopathies: 1. how the carrier state has no
disadvantages, 2. homozygous state that is associated with a very severe manifestation that could eventually
become fatal) and 3. fetal diagnosis
which is available and completely safe
Financial support
In today's era, a huge chunk of people are affected with homozygosity and heterozygosity of Hb disorders,
therefore a need for trained manpower that executes control programs (such as social workers, technicians,
doctors, counsellors) rises and so does the purchase of equipments, the record keepings and the information
system.
Technology
A routine practice of diagnosis involves a RBCS count with its indices, a Hb electrophoresis, microcolumn
chromatography, Hb F estimation, cation exchange high performance liquid chromatography (CE-HPLC). Also, a
high-end laboratory techniques like electrospray mass spectrometry or MALDI-TOF could be used to determine
the exact location of variations. Thus, technology has reached an epitome of success with respect to diagnosing
Hb disorders.
Preventive programs for Hb Disorders
These programs are based on detecting heterozygous individuals and counselling
them against marriages between carriers without prenatal diagnosis of their partners.
Preventive programs alone have effectively reduced the birth of thal major infants in
countries like Cyprus, Greece and Italy. However, preventive measures have a long way
to go in India, wherein cultural and ethnic walls
are build too high to break through!
As mentioned earlier, Asians are at a higher risk for Hb disorders and blaming a failed attempt at counseling
or a reckless attitude towards preventive healthcare won't be preposterous! No individual would intentionally
want to initiate the downfall of their family, community or society; and hence strategie screening programs,
well-established accurate, affordable and reachable molecular techniques and timely prenatal diagnosis is
certainly a prerequisite. Why blame the bygone beliefs of discrimination and constricted ethnic cultures,
when all it requires is a new perception!
