We’re in the midst of a revolution in genetics and the search for causes of genetic disorders. However, there has been a large hole in the data: Only 3 percent of participants in genetic studies to date are of African descent, while 80 percent are of European descent.
This is ironic because Africans have much more genetic diversity than Europeans. However, a recent study has examined the genetic changes associated with schizophrenia in Xhosa individuals from South Africa.
The Xhosa people primarily live in the Eastern Cape region of southern Africa, and they speak a language with clicks on many of the consonants. Scientists were interested in studying the Xhosa because they have a higher prevalence of schizophrenia than other populations.
Humans evolved in Africa 5 to 6 million years ago, and 99 percent of human evolution occurred before humans migrated to Europe and Asia. A small population migrated, leaving much genetic diversity behind in Africa. The scientists wanted to compare the genetic changes found in European schizophrenics with those from Africa.
The term schizophrenia comes from the Greek words “schizo,” meaning split and “phren,” which means mind. Schizophrenia is a disabling chronic neural disorder, affecting how people think, feel, behave and deal with reality.
Schizophrenia usually starts between 16 and 30 years of age. Symptoms include hallucinations, delusions, altered emotions and behaviors, reduced speaking, difficulty in focusing and problems using information immediately after learning it.
Scientists wanted to identify genetic changes associated with schizophrenia in the Xhosa population in South Africa. Previous studies have identified numerous schizophrenia susceptibility genes, but none of them are crucial for the development of this disorder. It’s likely that changes to more than one gene leads to schizophrenia.
The researchers recruited 909 people with schizophrenia and 917 control subjects of similar age, gender and place of residence. Scientists isolated the subjects’ DNA and sequenced the portions that coded for proteins. As expected, the Xhosa genetic variation was much greater than non-African populations. The researchers studied common and rare variants in the DNA they isolated.
The genetic variants the scientists found were in genes that play roles in the brain and brain development. These findings are similar to those in European or Asian populations. Many of the patients had unique variants, sometimes with more than one change in the same gene. They also discovered “damaging” variants, which resulted in alterations in the proteins they encoded. These variants likely represent newly arisen changes that contribute to schizophrenia.
The brain contains about 100 billion neurons, which are connected by synapses. The synaptic connections are always changing and are important in learning, memory and personality. A single neuron can have up to 15,000 synaptic connections. Disruptions in synapse messaging result in a variety of psychiatric disorders, including schizophrenia.
This new study, combined with existing data, suggests schizophrenia begins in development, though symptoms become more pronounced later in life. The complexity of the signal processes between nerves has hampered the development of a cure for this devastating disease.