Older Dads Can Pass on Gene Mutations That Lower Intellect

  • Study suggests changes in chromosomes may account for some cases, especially in older fathers.
  • Stress May Affect Preemies’ Brains, Study Shows

Certain genetic abnormalities in a man’s chromosomes appear to be linked to intellectual disabilities in his offspring, especially if he fathered them late in life, a new study suggests.

These abnormalities are caused by what are called “copy number variations” in genes. These include missing, repeated, inverted or misplaced DNA sequences, the researchers explained.

“While it is commonly known that the risk of birth defects such as Down Syndrome increases with maternal age, this study shows that an increased paternal age is also an important factor,” said study author Jayne Hehir-Kwa, from the department of human genetics at the University of Nijmegen in the Netherlands.

She said that scientists “are still trying to understand how many of these genetic mutations actually occur. This study has provided an important starting point, providing insight into how these mutations are formed.”

The type of genetic mutations studied were typically found in children with an IQ less than 70, Hehir-Kwa said. These kids often have other congenital abnormalities such as heart defects, she added.

Dads are more often the source of these gene aberrations than moms: In about 70 percent of cases, deletions and duplications of DNA responsible for intellectual disability were inherited from the father, Hehir-Kwa said.

Paternal age seemed key. “In many cases these fathers are, on average, significantly older, by two years, than fathers of children without intellectual disability,” she said.

However, because these outcomes remain very rare and the incidence of these mutations in men isn’t known, it is not yet possible to assign a specific level of risk for having a child with an intellectual disability, the researcher noted.

“To be able to directly translate these findings into patient management is still too soon at this stage,” Hehr-Kwa said.

The report was published in the Oct. 3 online edition of the Journal of Medical Genetics.

For the study, Hehir-Kwa’s team looked for copy number variations in over 3,400 people with intellectual disabilities between 2006 and 2010.

They found that 227 of those studied had new copy number variations, which were not inherited.

An in-depth analysis of the parents of 118 of the participants revealed that the variations of 90 of the 118 came for the father. And 75 percent of these variations were missing DNA sequences.

Among the group with non-repetitive DNA sequences — which accounted for most variations — older fathers were significantly associated with a child with intellectual disability, the researchers found.

Based on these findings, the researchers conclude that copy number variations occur more in fathers than mothers and that age also plays an important role.

Dr. Robert Marion, chief of genetics and development medicine and director of the Center for Congenital Disorders at the Children’s Hospital at Montefiore Medical Center in New York City, said that “the study provides some evidence for what we had suspected.”

“This study verifies that older fathers are more at risk to have children with intellectual disability, and the basis for this is changes in the DNA that lead to copy number variants,” Marion said.

Another expert, Dr. Stephanie Sacharow, an assistant professor of clinical and translational genetics at the University of Miami Miller School of Medicine, added that men cannot be tested for these variations at this time. That’s because the variations are only found in sperm, which is constantly changing.

“Over time, men are more likely to have new mutations. This is not something that can be predicted based on a man’s age, because most older men will have normal children,” she stressed. “But the risk to an older man of having a genetic issue which could lead to intellectual disability is going to be higher as he ages.”


Stress May Affect Preemies’ Brains, Study Shows

  • Intensive-care stressors range from diaper changes to invasive procedures.

Very premature babies may develop brain changes as a result of stress experienced in the neonatal intensive care unit and should receive follow-up care to monitor brain function into childhood, a new study suggests.

Stressors, ranging from diaper changes to intubation, may contribute to smaller brains and abnormal motor behavior, according to the study, published Oct. 4 in Annals of Neurology.

“Our findings suggest that stress exposure reduces the brain size in early preterm infants and long-term consequences are unknown,” study co-leader Dr. Terrie Inder, researcher at St. Louis Children’s Hospital in Missouri, said in a journal news release. “However, prior research has found that brain volume at (term) birth is a predictor of neurodevelopmental outcomes later in childhood.”

In conducting the study, researchers began observing 44 preterm infants born before 30 weeks’ gestation within 24 hours of their birth. They measured the stress these infants were exposed to, ranging from routine nursing care to invasive medical procedures, and evaluated their brain structure and function using MRI scans.

The babies’ average daily exposure to stressors was greatest within the first two weeks of life. Increased stress was linked to decreased frontal and parietal brain width, the study found. The investigators also found the babies’ brains had altered microstructure and functional connectivity within the temporal lobes.

Infants exposed to greater amounts of stress in the first two weeks of life also had abnormal movement patterns and lower reflex scores, the findings showed.

The study authors noted more research is needed on stress exposure among premature infants to improve these results.

According to background information in the news release, about 12 percent of pregnancies in the United States result in preterm births — before 37 weeks’ gestation, and up to 60 percent of these children display social difficulties, cognitive problems and emotional issues.

Each year, nearly 500,000 babies are premature, or preemies. That’s 1 of every 8 infants born in the United States. A premature birth is when a baby is born before 37 completed weeks of pregnancy. A full-term pregnancy is 40 weeks.

Important growth and development occur throughout pregnancy – especially in the final months and weeks. Because they are born too early, preemies weigh much less than full-term babies. They may have health problems because their organs did not have enough time to develop. Preemies need special medical care in a neonatal intensive care unit, or NICU. They stay there until their organ systems can work on their own.


More information

For more information on genetic birth defects, visit the U.S. National Library of Medicine

The U.S. National Library of Medicine has more about premature babies


(MONDAY, Oct. 3 (HealthDay News By Steven Reinberg, Reporter) -- SOURCES: Jayne Hehir-Kwa, Ph.D., department of human genetics, University of Nijmegen, the Netherlands; Robert Marion, M.D., chief, genetics and development medicine, and director, Center for Congenital Disorders, Children's Hospital at Montefiore Medical Center, New York City; Stephanie Sacharow, M.D., assistant professor, clinical and translational genetics, University of Miami Miller School of Medicine; Oct. 3, 2011, Journal of Medical Genetics)
TUESDAY, Oct. 4 (HealthDay News) -- Stress May Affect Preemies' Brains, Study Shows (SOURCE: Annals of Neurology, news release, Oct. 4, 2011)
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