ALLISON and Liam Holland were devastated when their 21-month-old son Elijah died suddenly five months ago.

Now the couple face more heartbreak after extensive genetic testing revealed their nine-month-old son Asher has the rare condition that killed his brother.

MECP2 duplication syndrome has no known cure. There are only 44 known cases in 18 families worldwide.

The syndrome mostly affects boys, who begin to lose their speech, mobility and functioning between six months and 18 months. Many die in childhood and most before they reach 25.

"We're completely overwhelmed and still in shock but we've found a new strength and want to do everything we can to make sure he gets the life he deserves and reaches his full potential," Mrs Holland said.

The couple, from Belmont near Newcastle, hope experimental trials under way in the United States and Europe may lead to the discovery of a drug to reverse or neutralise the duplicate MECP2 gene, which causes autistic-like traits, low-muscle tone, mental retardation, absence of speech, progressive spasticity, seizures and respiratory infections.

Huda Zoghbi, professor of molecular and human genetics at the Baylor College of Medicine in Texas, is testing a drug on mice. She hopes to develop a medicine in one to five years that will reverse the effects of having an extra gene.

She is working with Hilde Van Esch in Belgium, who discovered the duplication in 2005 using array-comparative genome hybridisation, which scans a patient's entire DNA and compares it to normal DNA to identify the faulty gene.

Testing recently began at John Hunter Children's Hospital in Newcastle. Pediatrician Don Anderson said more Australian families with MECP2 duplication may now be discovered.

MECP2 duplication syndrome is X-linked, which means a woman who carries the duplicate gene is asymptomatic but has a 50percent chance of passing it on to her son.

lhall@fairfaxmedia.com.au