Early speech, vocalization changes may signal Rett syndrome: Study
Researchers analyzed recordings made by twin sisters, one with MECP2 mutation
Early changes in speech, including fewer varied sounds, may signal Rett syndrome before obvious developmental delays and this may help doctors reach a diagnosis sooner, a study of twin girls who didn’t share the same genetic makeup suggests.
One twin developed normally, but the other, who was later diagnosed with Rett syndrome, began producing fewer and less complex sounds during her second year of life, and showed early signs of slowing and then regressing.
“This twin study provides a unique perspective that deepens our understanding of early speech-language developmental profiles in [Rett syndrome], especially in light of the intertwinement of genetic, individual, and contextual factors,” the researchers wrote. The study, “Shared Environment-Different Genes: Speech-Language Development in a Pair of Dizygotic Twins with and Without MECP2 Mutation,” was published in The Journal of Genetic Psychology.
Rett syndrome is often caused by mutations in MECP2, a gene that provides instructions for producing a protein that’s important for normal brain development. A shortage of the MeCP2 protein interferes with how nerve cells function, causing symptoms. After birth, girls with Rett syndrome develop seemingly normally for 6 to 18 months before beginning to have severe problems with language and communication, learning, and movement. There’s growing evidence of early changes in the first year of life before these obvious delays manifest, however.
One twin diagnosed with Rett syndrome
Here, audio recordings from home videos were used to analyze early speech changes in twin girls in Germany during their first two years of life. The researchers focused on how complex the girls’ speech was, the qualities of their voices, and the variety of sounds they made.
The girls were born at 38 weeks, after a normal pregnancy, as dizygotic (fraternal) twins, meaning two separate eggs were fertilized by two different sperm cells during the same pregnancy. Just like other siblings who aren’t twins, they share half their genetic makeup.
The first girl developed normally from birth and passed all her routine medical and developmental examinations. She didn’t receive any clinical diagnoses and followed a regular education, completing school with a college-entry qualification.
Her parents had their first concerns about her sister after 6 months of age, as she was unusually quiet and had motor delays, such as not crawling. Despite regular medical exams, the second girl showed no problems in her first year of life. She could sit independently at 12 months, crawl at 15 months, and walk at 24 months, but with difficulty. The girl spoke her first words by the end of her first year and used two-word sentences in her second year. However, her speech development then slowed and she lost words. At 3 years and 7 months she was diagnosed with Rett syndrome by genetic testing for a disease-causing mutation in the MECP2 gene.
Analyzing speech differences, changes
Analyzing the audios showed both twins mostly made voiced sounds, with few unvoiced ones, in their first year, but by their second year, all the sounds from the first twin were voiced, while her sister still produced uncategorizable sounds.
In the first year, both girls mainly produced simple syllables, but the second girl spoke more syllables with one consonant and produced more canonical syllables, those formed by a consonant followed by a fully resonant vowel (23% vs. 13%). The first girl didn’t speak syllables with two consonants.
That “pattern reversed in the second year,” however. Most of the sounds produced by the second girl were noncanonical (65%), with only a few simple canonical syllables. More than half of the first twin’s sounds were canonical, including syllables with least two consonants.
After a more detailed audio analysis of the first year, the researchers observed that the first girl started making sounds at 3 months, at a younger age than her sister, who began at 5 months. Both reached canonical babbling by 6 and 7 months, respectively. Over time, however, the second twin produced fewer and less complex sounds, and by her second year, she produced only a few clear speech-like sounds. She also showed unusual patterns, such as high-pitched sounds, “crying-like, shrill, or shrieking sounds,” which occurred more frequently between 6 and 9 months.
The researchers said their findings should be interpreted with caution as the study was based on a small number of recordings. But comparing the sisters allowed them to explore how genetic and environmental factors influence speech development.
“In nearly all cases, the twins were recorded simultaneously, in identical social-communicative situations, and had comparable opportunities for vocalizing. However, we observed two distinct pathways in the twin’s early vocal development across their first 2 years of life,” the researchers wrote. “A better understanding and prediction of early developmental pathways — leading to the identification of specific conditions — could enable earlier, more targeted interventions tailored to individual needs, improving treatment efficiency and efficacy.”
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