Twins With Feingold Syndrome: Overview and Interview
Feingold syndrome is a condition that involves shortening of the second and fifth fingers, reduction in the size of the head and jaw, and fusion of the second and third or fourth and fifth toes. Type I includes blockage of the digestive system, whereas type 2 does not. I described this condition in a pair of 18-month-old MZ male twins in earlier issues of Twin Research and Human Genetics (Segal, Reference Segal2025a, Reference Segal2025b). In March 2026, there was an opportunity to meet the twins and their mother in person while I was attending a conference in Denver, Colorado. This article summarizes some previous information about the condition and the twins, and provides updates on their progress, based on an interview with their mother. The twins, at 2 years, 2 months of age, are shown in Figures 1a and 1b.
Monozygotic twins with Feingold syndrome, March 2026. Photo credit: Dr. Nancy L. Segal.
Monozygotic twins with Feingold syndrome, riding bikes, April 2026. Photo courtesy: Twins’ family.
The twins were classified as monozygotic (MZ) and monochorionic-diamniotic, based on their concordance for the MCYN gene (that is implicated in type 1), and their placentation. In addition, they are identical in appearance — even their mother confuses them if she is in a hurry. When the twins arrived at the hospital for a chest x-ray, there was momentary worry that the same boy had been assessed twice.
The pregnancy was unremarkable, with the exception of elevated maternal blood pressure; ultrasounds indicated that the twins were small in size, but that is not unusual for twins who are typically born prematurely. Feingold syndrome was not immediately recognized following the twins’ birth — their mother noted some slanting of the eyes as the twins matured, but trisomy 21 was ruled out. Instead, the characteristic features on the hands (e.g., presence of a Simian crease on the twins’ palms) and feet signaled Feingold syndrome. The twins’ heads remain a bit small, but an MRI revealed nothing of medical significance involving brain structure — this was the most worrisome aspect of the condition for their parents. Growth hormone was considered as a possible intervention for their reduced stature, but such medications can pose unintended side effects. The twins’ mother noted that the twins’ prematurity, combined with their condition, makes it difficult to assign causation to their various symptoms, such as atresia, which interferes with digestion. The twins do not experience reflux, but they do experience difficulties with chewing.
The twins show many traits in common. They generally prefer the same toys, so their parents purchase two of everything to avoid conflicts. However, the two little boys are closely connected to one another — they know each other’s names and call out to one another. Their current social interaction with other children is limited to their daycare center but will become more varied as they enter school. There seems to be no reason to encourage separation at present, although some separation may be attempted when they are older. However, it was noted that on the few occasions when the twins have been apart for several hours, they seem to be calmer and less distractable. Therefore, their mother wonders if some time apart would be a good occasional plan; she noted that they failed to follow instructions at soccer, so some separation may alleviate this problem. Of course, this is an issue faced by all families with young multiple birth children. In the future, the school separation issue will need to be decided — I suggested that the twins be placed in the same classroom, but be assigned to different groups — this arrangement would allow them to know that their cotwin is nearby which may offer the comfort and security they need, yet will give them exposure to other children. I also advised the twins’ mother to dress the twins in different outfits, or at least contrasting colors, so that teachers and classmates can distinguish between them.
The twins’ sleep is monitored by their parents, showing that they assume similar positions even as they shift during the night. In terms of behavior, one twin was considered to be more ‘wild’ than the other, yet they seem to have recently ‘exchanged places’, a behavioral phenomenon observed in other MZ twin pairs. A potential concern is that one twin might gain stature ahead of the other, a development that might differentiate them in a way that might be detrimental; however, there is no way to predict how their growth will proceed. They engage in many activities that are typical of young children; for example, bike riding and climbing. They have tiny guitars and enjoy listening to music — at daycare they were treated to a performance by a guitar player with a standard size instrument and enjoyed it. Their parents are doing everything possible to ensure that their twin children live happy and productive lives.
The twins currently receive therapy for physical development, speech, and feeding, although the frequency of such sessions is being reduced. One of the twins began jumping, which is a milestone of the second year of life, and they have started to engage in sports more actively. Feingold syndrome is usually associated with some learning disabilities that may be expressed over time; however, their mother wisely noted that many children experience difficulties with some cognitive skills.
The twins’ mother lamented that because of its rarity, Feingold syndrome does not receive a great deal of research attention; she believes that only about 200 people in the world are affected. She feels fortunate, however, that her twins do not have some of the more serious physical complications that concern cardiac and kidney functioning. In fact, when you meet the twins, they appear to be ordinary toddlers that look like any other pair of twins — their hands and fingers do not look unusual except when they are closely examined; still there is a concern that other children will notice these differences and tease them.
I encouraged their mother to reach out to groups and societies of parents with multiple birth children. It is important to reach others who may be experiencing similar situations or know other families whose twins are affected with Feingold syndrome. I believe an excellent venue would be the 2027 International Congress of Twin Studies that brings together parents, physicians, and investigators representing diverse disciplines and specialties. Another rare condition that would benefit from a twin research perspective is Steinert disease, a form of muscular dystrophy (National Organization for Rare Disorders, 2026). Note that mothers and fathers are in the unique position of having access to nearly every behavior and symptom their children express. They may be able to provide information to specialists that is unavailable elsewhere. I look forward to staying in touch with the twin pair discussed in the present article, as well as their parents, and plan to bring further updates to the readers of Twin Research and Human Genetics.
Twin Research Summaries
Pseudomonoamniotic Twins
Amniotic twins (twins encased in a single amnion or inner fetal membrane) are rare, occurring in 1−2% of MZ twin pregnancies. This prenatal circumstance poses considerable morbidity and mortality risks to the developing fetuses. Two related twin cases involving another rare condition were described by Kong et al. (Reference Kong, Wu, Sun, Qin, Wang, Zhu and Chen2025) from China. The condition, known as pseudomonoamniotic twins, occurs when the dividing membrane ruptures, leading to malformations and possibly fetal death. It may be caused by invasive procedures performed on diamniotic twins. In the first case under study, an emergency cesarean section delivery was undertaken. In the second case, the twins were cared for in the neonatal intensive care unit until discharge at age 50 days when their condition appeared favorable. It was suggested that targeted evaluation of the dividing membrane at umbilical cord insertion sites may improve the detection of spontaneous pseudomonoamniotic twins.
Selective Fetal Growth Restriction in Monoamniotic Twins
A comprehensive review of research on selective fetal growth restriction (sFGR) in monochorionic twins highlighted new developments and future directions in this area. The Gratacós classification (types I, II, and III) based on umbilical artery Doppler flow (direction and speed of blood flow), is recommended for identifying the degree of risk. This classification system is as follows (Mustafa et al., Reference Mustafa, Javinani, Heydari, Saldaña, Rohita and Khalil2023):
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• Type I: selective intrauterine growth restriction cases with positive end-diastolic flow.
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• Type II: cases with persistently absent end-diastolic flow.
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• Type III cases with intermittent absent or reversed end-diastolic flow.
Type 1 cases can be managed if anticipated, whereas types 2 and 3 require intervention. The researchers call for randomized trials to assess the efficacy of the new imaging, biomarkers, and intervention techniques.
Twin Authorship Attribution
I have served as an expert witness on cases of alleged cheating by MZ twins. I am also aware of incidents in which twins are accused of cheating when they produce similar work. It was, therefore, of interest to find a study in which the writing styles of three sets of MZ cotwins were compared (Mohamed, Reference Mohamed2026). Machine learning proved able to distinguish between cotwins who were not more similar to one another than to the members of the other pairs. Many aspects of the twins’ writing were examined, but the key distinguishing features were Function Words (words that connect sentences, such as ‘the’ and ‘over’; Nordquist, Reference Nordquist2024), Part-of-Speech Tags (the process of assigning a word as corresponding to a part of speech based on its definition and its relationship with adjacent and related words; Pham, Reference Pham2020), and Dependency Labels (identification of related words and the relationship between them; Jaiswal, Reference Jaiswal2021). Caveats to this study are the very small sample and the lack of information regarding the method by which the twins were classified as MZ.
Twins Discordant for Clubfoot
One of the few twin studies of clubfoot was conducted by Katz et al. (Reference Katz, Kreiner, Blank and Lebel2025) at the Shaare Zedek Medical Center, in Jerusalem, Israel. According to the authors, clubfoot is a congenital condition that occurs in an estimated 1−2 out of 1000 live births. The study sample included 13 twin pairs, 2 of whom were MZ and 11 of whom were dizygotic (DZ). The twins, who ranged in age from 6 months to 7 years, were identified from a clubfoot database that included approximately 400 patients; however, of the 31 pairs initially identified, 10 failed to meet the age criteria, 6 declined participation, and 2 did not attend the evaluation. All pairs included an affected twin and an unaffected cotwin. All twins completed the Mullen Scales of Early Learning (MSEL), a test designed to assess cognitive and motor developmental milestones. No meaningful differences were detected between affected and unaffected twins, leading to the conclusion that clubfoot does not impair the specific skills under study. Unfortunately, the sample was quite small and the method by which the twins were classified as MZ or DZ was not provided.
Human Interest
Twins with Different Fathers
Lavinia and Michelle Osborne are 49-year-old British twins who enjoy being twins (Kleeman, Reference Kleeman2026). Raised by a single mother, they always puzzled over the identity of their father — they were aware that some twins do not share their paternal parent. They were only told that their father was named James, and surmised that James was their mother’s partner. Interestingly, Lavinia recognized features of herself in James, but Michelle never did. Several years ago, at age 45, they decided to undergo a DNA test to settle the matter. It turned out that Lavinia and Michelle are heteropaternal twins, sharing an average of 25% of their DNA, like the half-siblings they are. Lavinia was devastated by the news — ‘For about a month, I couldn’t stop crying … [Michelle] was the one thing that belonged to me. The one thing I was sure of. And then she wasn’t.’
Of course, Lavinia and Michelle are still twins — even ordinary fraternal twins who share an average of 50% of their genes can vary considerably in their degree of genetic relatedness. The article indicated that heteropaternal twinning is rare, stating that fewer than 20 cases have been identified. I have argued elsewhere that the cases we know of are those that have been medically documented; however, I have come across other heteropaternal twin pairs and I trust that others have been overlooked (Segal & Nedelec, Reference Segal and Nedelec2021). It is also of interest that one twin was certain of her relatedness to their alleged father, whereas the other twin was not. How we know who our relatives are is a fascinating and complex question of particular significance to evolutionary researchers.
Biological Relatedness in a Married Couple
A married Brazilian couple from São Paulo, Adriana and Leandro, are brother and sister; however, they did not know that when they fell in love and married. They are raising a 6-year-old daughter. Their relatedness was discovered when both spouses began to search for the mothers who had abandoned them as children (Eleftheriou-Smith, Reference Eleftheriou-Smith2014). They thought it was coincidental that their mothers were both named Maria, even though Maria is a common name in their country. Adriana finally called into a radio show, ‘The Time is Now’, on Globo Radio, and spoke to her mother. It was then that her mother told her she had had a son named Leandro. The couple was shocked but has stayed together. There was no mention in the article of a DNA test performed to confirm their full sibling relationship, which is the same as that of fraternal twins.
While dating, Adriana and Leandro apparently experienced genetic sexual attraction (GSA). GSA is the strong sexual attraction felt by some separated biological relatives following reunion (Gonyo, Reference Gonyo1987). Some people who experience this phenomenon know they are meeting a relative, but that is not always true, as happened with the Brazilian couple. Note that the Brazilian case does not involve twins yet is relevant to twins in that several sets of opposite-sex twins have met and married. Most married twins discovered their true relationship when they had a child with a recessive genetic disease — this birth outcome is more likely if a child is conceived by close relatives who tend to carry the same detrimental gene, albeit in an unexpressed form (Segal, Reference Segalin press).
Birth of Identical Quadruplets
The rare birth of female identical twins captured the attention of both medical professionals and the fascinated public (Abrahamson, Reference Abrahamson2026). The infants, named Amora, Analia, Arya and A’zura, were born to a Corpus Christi, Texas couple Adriana Luna and Anthony Lerma; the couple already had a 3-year-old son. The quads were delivered on February 14, 2026, at 29 weeks and 4 days’ gestation. Each baby weighed slightly over 3 pounds and spent their early weeks in the neonatal intensive care unit. Interestingly, their father has an identical twin brother.
It is generally believed that identical twinning is not genetically influenced, while fraternal twinning is a maternally transmitted tendency. However, recent studies suggest that identical twinning may run in some families and that twinning on the paternal side of the family may be possible; additional research in this area is warranted (Segal, Reference Segalin press).
Twins Switching Places
The Kriner twins, Dana and Delanie, look identical in appearance, no doubt explaining why they enjoy the annual Twins Days Festival, in Twinsburg, Ohio — the twins have served as ambassadors for the Royal Court and been part of the parade float (People Magazine, 2023). However, the twins have somewhat different personalities and interests. Dana, the decision maker, is more reserved, whereas Delanie is more extraverted and talkative. Both twins attended the University of Toledo, in Ohio, but pursued different areas of study. Dana majored in criminal justice and minored in psychology, while Delanie majored in healthcare and. minored in business. Dana is now a police officer and Delanie is a nursing home administrator. However, their matched looks allowed them to successfully exchange places on nine occasions. They were discovered just once — as college students they substituted for one another if one twin was out of town, in order to be marked present. However, when Dana could not recall Delanie’s seat assignment, she asked another student and was overheard by the instructor — the instructor was not pleased, citing possible interference in the event of an emergency situation.
