Gene causing motor development disorder found

In a discovery that is paving the way for the diagnosis and treatment of a rare genetic disorder related to the brain's functioning, a team of researchers has identified the causative gene behind the disease, which delays development of motor activities in children.

The study was done on a four-year-old child from Punjab, and nine other children who were suffering from motor developmental delay. They could not walk and sit without support.

The team, led by Ryan Taft of the University of Queensland's Institute for Molecular Bioscience (IMB), comprised 16 researchers including I.C. Verma, director, Centre for Medical Genetics, Sir Ganga Ram Hospital and Monica Juneja, Department of Paediatrics, Maulana Azad Medical College.

The doctors used genome sequencing to determine that these children were suffering from a defect in a gene previously not associated with human disease.

"It has been found that mutations in a gene called DARS gene is responsible for causing inherited brain disorder called HBSL (Hypomyelination with Brain Stem and Spinal Cord Involvement and Leg Spasticity), which affects the motor development activities," a statement from the doctors said.

"We analysed the genome sequences of this child and his parents, using a method called whole genome sequencing and found that a mutation in the DARS gene was likely causing the disorder," Taft said.

"In collaboration with clinicians from India, Canada, Netherlands, Australia, and the US, we then examined the genomes of nine other children who appeared to be suffering from the same disease and the genomes of their parents, and confirmed that they all had mutations in the DARS gene," he said.

"This gene has never previously been associated with human disease and may not have been identified as the culprit using any other method," said Verma, who heads the department of genetics at Sir Ganga Ram Hospital.

Experts from Sir Ganga Ram Hospital and Maulana Azad Medical College, Delhi, India and IMB in Brisbane, Vrije Universiteit Medical Center in Amsterdam, Murdoch Children's Research Institute and The Royal Children's Hospital in Melbourne, and Children's National Medical Centre in Washington D.C came together for this research.

Verma elaborated: "They have named the disease HBSL because it causes Hypomyelination in the brain stem and spinal cord, leading to leg spasticity. Hypomyelination occurs when people do not have enough myelin, the substance that coats nerve fibres and enables the transmission of electrical impulses in the nervous system."

"Our goal is to dramatically reduce the number of unresolved paediatric cases of the rare genetic disease," said Taft.

The technology of exome sequencing and whole sequencing now allows doctors to find the cause of disease in many children with unknown brain disorders. The doctors say they have used exome-based targetted next generation sequencing to identify the culprit gene in other patients also.

At present 30 to 40 percent of patients with intellectual disability go undiagnosed in India. Doctors say the new techniques will remarkably reduce this number.

"Discovering the causative gene will help in providing genetic counselling to the family. It will also ensure that they have normal children," Verma said.

"This is the future of medicine - doctors, including clinical specialists like MRI experts - and genomics researchers working together to diagnose and develop treatments for people with unknown diseases," he added.