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When twin brothers in Italy developed similar Covid-19 symptoms, doctors expected the infection in both would follow similar clinical courses, but while one recovered relatively quickly, the other became critically ill and required an ICU stay—and doctors can't explain why, according to case study in the Annals of Internal Medicine.
The case study was described in a letter submitted to the journal, written by Davide Lazzeroni of Fondazione Don Carlo Gnocchi in Italy and his colleagues.
Striking similarities
According to the case study, the twins—considered homozygous because of their physical appearance and shared characteristics—had a striking number of similarities beyond their shared genetic background. Both men, aged 60, lived at the same address and "worked at the same job in the same workplace," an auto shop.
Furthermore, the twins shared the same vaccination schedule and had similar diets. And both likely caught the virus from the same shop customer—meaning they "acquired the same virus"—and both had similar "viral load at diagnosis," the authors wrote.
Moreover, at the start, the disease seemed to take the same trajectory in both of them. After experiencing symptoms for 10 days, ranging from fever to a dry cough, the twins were both admitted to the hospital with mild interstitial pneumonia. While hospitalized, both received supplemental oxygen and experimental treatments, including paracetamol and hydroxychloroquine—and both receive these treatments from the same medical team, with the same level of dosages.
However, after 12 days at the hospital, one twin was discharged and soon recovered—while the other twin steadily declined. This latter twin was eventually transferred to the ICU for mechanical ventilation, where he soon "developed septic shock from an anaerobic bacterial infection that required vasopressors, antibiotics, steroids, and four days of invasive ventilation." Once released from the ICU, he remained in the hospital for another 17 days before he recovered sufficiently for discharge.
The brothers did share one notable difference, the authors found: The one with the milder experience of Covid-19 was married, while the one with the more serious case was single. But the researchers still don't know precisely what caused one to fare so much worse than the other—and they said they plan to conduct "further investigations (genetic, epigenetic, metabolic, immunological, and microbiological) … to improve the knowledge of Covid-19 pathophysiologic mechanisms," they wrote.
That said, the researchers did note that the case study suggests genetics likely don't dictate the differences in severity of illness.
However, Nancy Segal, a professor of psychology and director of the Twin Studies Center at California State University-Fulton, said the current lack of DNA confirmation that the twins are monozygotic, or identical, makes any conclusions difficult. Moreover, "if we assume that the twins are" identical, "there are many factors that could explain their discordance," she said, such as their exposure to non-shared environments, any potential birth weight differences or in-utero differences, and more (Remaly, MedScape, 12/15; Lazzeroni et al. Annals of Internal Medicine, 12/8).
The brothers did share one notable difference, the authors found: The one with the milder experience of Covid-19 was married, while the one with the more serious case was single. But the researchers still don't know precisely what caused one to fare so much worse than the other—and they said they plan to conduct "further investigations (genetic, epigenetic, metabolic, immunological, and microbiological) … to improve the knowledge of Covid-19 pathophysiologic mechanisms," they wrote.
That said, the researchers did note that the case study suggests genetics likely don't dictate the differences in severity of illness.
However, Nancy Segal, a professor of psychology and director of the Twin Studies Center at California State University-Fulton, said the current lack of DNA confirmation that the twins are monozygotic, or identical, makes any conclusions difficult. Moreover, "if we assume that the twins are" identical, "there are many factors that could explain their discordance," she said, such as their exposure to non-shared environments, any potential birth weight differences or in-utero differences, and more (Remaly, MedScape, 12/15; Lazzeroni et al. Annals of Internal Medicine, 12/8).
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