Study gives insight into significance of genetic sequencing to diagnose growth disorders

The study highlights the need to use broad genetic tests such as whole exome or whole genome sequencing to identify the rare diseases.

Brazilian researchers described the case of a nine-year-old boy admitted to the hospital with multiple symptoms and overlapping conditions that made diagnosis difficult, including short stature, thin tooth enamel (dental enamel hypoplasia), moderate mental deficiency, speech delay, asthma, mildly altered blood sugar, and a history of recurring infections in infancy. The article was published in the Journal of Pediatrics.

The scientists searched for genetic alterations in GCK and BCL11B using exome sequencing, which analyses only the protein-coding region of the genome. They discovered them. As a result, monogenic diabetes and T-cell abnormalities syndrome were identified as rare disorders. The identification of the actual cause of the problem, as well as the detection of a blood sugar change, had a substantial impact on their treatment decision.

This is one of six cases involving syndromic growth disorders with multiple genetic diagnoses (two or more distinct genetic conditions in the same patient) described in the article, which concerns a study conducted by researchers at the University of Sao Paulo's Medical School (FM-USP).

The team sequenced the exomes of 115 patients with syndromic growth disorders that had hitherto unknown causes, diagnosing 63 on the basis of the genetic analysis; 9.5% of these had a multiple diagnosis, far more than in previous studies.

"The cases involved two or more rare monogenic conditions in the same patient. Such cases are very hard to diagnose, especially by clinical assessment alone. The study highlights the need to use broad genetic tests such as whole exome or whole genome sequencing for these patients as the only way to identify the rare diseases that explain such clusters of conditions," Lima Jorge said.

There are numerous rare diseases, including growth disorders, so it is naturally difficult to identify many of them, he added. Between 5% and 10% of the world population is believed to have a rare disease.

Short stature or tall stature is not a diagnosis but a clinical finding. "Short stature may have an external cause, such as an infection or malnutrition. Even so, genetic factors will always be important to growth. In healthy children with short or tall stature as the only manifestation, there will probably be a polygenic basis [where stature is influenced by several genetic variants], but in syndromic growth disorders, in which short or tall stature is accompanied by other findings such as mental deficiency, deafness, autism spectrum disorder or malformation, an alteration in one or more genes is more likely as a justification for the complex phenotype involved," Lima Jorge said.

In light of the results, the researchers advocate recognition of multiple genetic diagnoses as a possibility in complex cases of growth disorder, opening up novel prospects for treatment and genetic counselling for such patients, in place of the typical paradigm that calls for a single diagnosis to explain all findings.

In the article, the researchers state that the development of next-generation sequencing techniques such as whole exome or whole genome sequencing has made selecting a single gene as the candidate to explain a case unnecessary. This particular benefit has proved useful in the research environment to foster the discovery of novel disease-associated genes, to further the study of conditions with a high degree of genetic heterogeneity, and to help care for patients with complex syndromic conditions, where diagnoses cannot be obtained by traditional clinical and genetic methods.

Several challenges noted by Lima Jorge include the high cost of genetic tests and the fact that exome sequencing has a success rate of about 50% in the diagnosis of complex cases. In other words, about half the patients submitted to this kind of analysis will have to go on looking for a conclusive diagnosis.

This story has been published from a wire agency feed without modifications to the text.