"The common thinking in the past had been that Rett syndrome only affects girls, and that the genetic flaw would be so serious in boys that they would die before birth," Dr Leonard said.

"Worldwide there have only been 11 previously established cases in boys who have presented early in life with a severe clinical picture of progressive neurological decline and breathing abnormalities starting soon after birth. All but two had a family history of a girl in the family with Rett syndrome. This study has confirmed a further four cases with no family history."

The study, published in the international journal Neurology, was a collaborative effort between researchers from Australia and the United States.

"Genetic testing is used to diagnose Rett syndrome in girls who present with typical symptoms after the age of one year. Prenatal diagnosis is also available in subsequent pregnancies for mothers of girls with Rett syndrome but beyond these families, doctors generally wouldn't test for the problem -- especially in baby boys," Dr Leonard said.

"It is likely that some baby boys with early severe progressive encephalopathy could go undiagnosed and we encourage paediatricians to think about this as a possible cause of severe neurological abnormalities."

Dr Leonard said one of the cases was managed by Princess Margaret Hospital Paediatrician Dr Jackie Scurlock. The genetic testing for that case was undertaken by Dr Mark Davis and Professor Nigel Laing at the Neurogenetics Laboratory at Royal Perth Hospital.

"While sadly the child had died at 14 months of age, it has been important for the parents to finally have a diagnosis, even after his death," Dr Leonard said.

Rett syndrome (RTT) is a neurological disorder often misdiagnosed as autism, cerebral palsy or non-specified developmental delay caused by a defective regulatory MECP2 gene found on the X chromosome. The disorder is seen almost exclusively in females. Unlike females, who have two X-chromosomes, males have an X and a Y chromosome. Because males lack a "backup" copy of the X chromosome that can compensate for a defective one, flaws in MECP2 are often lethal to the male fetus. RTT occurs in a variety of racial and ethnic groups worldwide and is now known to occur in 1:10,000 to 1:23,000 female births, but incidence may be far greater as new genetic evidence is discovered.

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