Female Twins Research Articles

Anorexia nervosa polygenic risk, beyond diagnoses: relationship with adolescent disordered eating and behaviors in an Australian female twin population.

It is well established that there is a substantial genetic component to eating disorders (EDs). Polygenic risk scores (PRSs) can be used to quantify cumulative genetic risk for a trait at an individual level. Recent studies suggest PRSs for anorexia nervosa (AN) may also predict risk for other disordered eating behaviors, but no study has examined if PRS for AN can predict disordered eating as a global continuous measure. This study aimed to investigate whether PRS for AN predicted overall levels of disordered eating, or specific lifetime disordered eating behaviors, in an Australian adolescent female population. PRSs were calculated based on summary statistics from the largest Psychiatric Genomics Consortium AN genome-wide association study to date. Analyses were performed using genome-wide complex trait analysis to test the associations between AN PRS and disordered eating global scores, avoidance of eating, objective bulimic episodes, self-induced vomiting, and driven exercise in a sample of Australian adolescent female twins recruited from the Australian Twin Registry (N = 383). After applying the false-discovery rate correction, the AN PRS was significantly associated with all disordered eating outcomes. Findings suggest shared genetic etiology across disordered eating presentations and provide insight into the utility of AN PRS for predicting disordered eating behaviors in the general population. In the future, PRSs for EDs may have clinical utility in early disordered eating risk identification, prevention, and intervention.

Dystocia due to Twin Pregnancy in HF Crossbred Cattle- A Case Report

Background: Freemartinism is one of the most commonly found intersex conditions in cattle, although it may also occur in small ruminants. The freemartin phenotype appears in a dizygotic twin pregnancy where one twin is a male and the other is a female. Due to precocious anastomoses between the placental vascular systems of the two fetuses, masculinising molecules reach the female twin and disrupt the normal sexual differentiation. In cattle, this condition is observed in 90 to 97% of twin pregnancies. A freemartin is, by definition, a genetically female fetus masculinised in the presence of a male co-twin, giving rise to a sterile heifer. Methods: A HF crossbred cow of 2nd parity was presented at Veterinary Clinical Complex, College of Veterinary Science and Animal Husbandry, Mhow (M.P) with the history of difficulty in calving, uterine contraction since last night, restlessness, uterine fluid discharge from vagina and swollen vulva. Per vaginal examination revealed presence of two fetuses in the uterus one being in anterior while other being in posterior presentation. Result: Dystocia was resolved by manual intervention per vaginum resulting in birth of one male and one female calf. The male calf was strong and active, while the female calf was weak as compare to male.

Fabry disease in female monozygotic twins with complex intronic haplotype variants: a case report

BackgroundFabry disease is an X-linked lysosomal storage disease caused by the impairment of α-galactosidase A. The complex intronic haplotype (CIH) variants, located in promoter and intronic regulatory lesions, has been found in patients with classical forms of Fabry disease. We present a case of Fabry disease in female monozygotic twins exhibiting the CIH mutation and classical manifestations.Case presentationA 61-year-old woman with a history of stroke, carotid artery occlusion, hypertrophic cardiomyopathy, and chronic kidney disease was referred to the nephrology clinic for management of her chronic kidney disease. Her monozygotic twin sister also presented with hypertrophic cardiomyopathy, atrial flutter, carotid stenosis, and proteinuria. Clinical symptoms and a comprehensive family history strongly suggested the presence of Fabry disease. Genetic analysis revealed the presence of 5 variants within a complex intronic haplotype (CIH): c.−10 C > T, c.369 + 990 C > A, c.370 − 81_370–77delCAGCC, c.640–16 A > G, and c.1000–22 C > T. We conducted a review of the patient’s previous kidney biopsy findings, which demonstrated the presence of lamellated inclusion bodies in electron microscopy. Remarkably, both the monozygotic twin sister and her son exhibited the same genetic mutation. Enzyme replacement therapy was initiated for the patient. Her kidney function decreased throughout a thorough 2-year follow-up period, while there was a slight decrease in the left ventricular mass index.ConclusionsThis is the first reported case of female monozygotic twins with the CIH variants representing cardiac, cerebrovascular, and renal manifestations suggestive of Fabry disease.

Causal relationships between height and weight with distal tibia microarchitecture and geometry in adult female twin pairs.

Higher stature and lower weight are associated with increased risk of fracture. However, the pathophysiology for the associations of height and weight with bone microarchitecture and geometry is unclear. We examined whether these associations were consistent with causation and/or with shared familial factors. In this cross-sectional study of 566 female twins aged 26-76yr, a regression analysis for twin data, Inference about Causation by Examination of FAmilial CONfounding (ICE FALCON), was used for testing causation. The bone microarchitecture and geometry of the distal tibia was assessed using HR-pQCT and the StrAx1.0 software. Higher stature was associated with larger total bone cross-sectional area (CSA), lower total bone volumetric bone mineral density (vBMD), larger cortical CSA, thinner cortices, higher porosity of the total cortex, compact cortex, outer and inner transitional zone (TZ), lower cortical vBMD, and larger medullary CSA (regression coefficients (β) ranging from -.37 to .60, all p<.05). Using ICE FALCON, the cross-pair cross-trait associations attenuated toward zero after adjusting for the within-individual association (absolute values of β ranging from .05 to .31, all p<.001). Higher weight was associated with higher total bone vBMD, larger cortical CSA and thicker cortices, lower porosity of the total cortex and inner TZ, and higher cortical vBMD (β ranging from -.23 to .34, all p<.001), and thinner trabeculae, higher trabecular number, lower trabecular separation, and higher trabecular vBMD (β ranging from -.31 to .39, all p<.05). Only cortical CSA attenuated toward zero after adjusting for the within-individual association between weight and bone microarchitecture (β = .042, p=.046). Higher stature was associated with a weaker cortical, not trabecular bone traits, whereas higher weight was associated with stronger cortical and trabecular bone traits. The results were consistent with height having a causal effect on weaker cortical bone structure, whereas weight had a casual effect on the larger cortical CSA.

Genetic effects on the skin methylome in healthy older twins

Whole-skin DNA methylation variation has been implicated in several diseases, including melanoma, but its genetic basis has not yet been fully characterized. Using bulk skin tissue samples from 414 healthy female UK twins, we performed twin-based heritability and methylation quantitative trait loci (meQTL) analyses for >400,000 DNA methylation sites. We find that the human skin DNA methylome is on average less heritable than previously estimated in blood and other tissues (mean heritability: 10.02%). meQTL analysis identified local genetic effects influencing DNA methylation at 18.8% (76,442) of tested CpG sites, as well as 1,775 CpG sites associated with at least one distal genetic variant. As a functional follow-up, we performed skin expression QTL (eQTL) analyses in a partially overlapping sample of 604 female twins. Colocalization analysis identified over 3,500 shared genetic effects affecting thousands of CpG sites (10,067) and genes (4,475). Mediation analysis of putative colocalized gene-CpG pairs identified 114 genes with evidence for eQTL effects being mediated by DNA methylation in skin, including in genes implicating skin disease such as ALOX12 and CSPG4. We further explored the relevance of skin meQTLs to skin disease and found that skin meQTLs and CpGs under genetic influence were enriched for multiple skin-related genome-wide and epigenome-wide association signals, including for melanoma and psoriasis. Our findings give insights into the regulatory landscape of epigenomic variation in skin.

Life in pairs: Estimating the impact of twin’s sex on child survival in India

This paper shows that in India, male twins with female co-twins have higher survival rates, but opposite results hold for female twins. Biological factors and differential resource allocation drive the results for male and female children, respectively.

Unprecedented report: First female monozygotic twins as carriers of Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford Progeria Syndrome (HGPS) is a rare genetic condition characterized by premature aging resulting from an autosomal mutation in the LMNA gene. This article presents a groundbreaking instance of the first female monozygotic twins affected by HGPS, originating from Brazil, highlighting the exceptional nature of this case.

Reversal of Autism Symptoms among Dizygotic Twins through a Personalized Lifestyle and Environmental Modification Approach: A Case Report and Review of the Literature

The prevalence of autism has been increasing at an alarming rate. Even accounting for the expansion of autism spectrum disorder diagnostic (ASD) criteria throughout the 1990’s, there has been an over 300% increase in ASD prevalence since the year 2000. The often debilitating personal, familial, and societal sequelae of autism are generally believed to be lifelong. However, there have been several encouraging case reports demonstrating the reversal of autism diagnoses, with a therapeutic focus on addressing the environmental and modifiable lifestyle factors believed to be largely underlying the condition. This case report describes the reversal of autism symptoms among dizygotic, female twin toddlers and provides a review of related literature describing associations between modifiable lifestyle factors, environmental exposures, and various clinical approaches to treating autism. The twins were diagnosed with Level 3 severity ASD “requiring very substantial support” at approximately 20 months of age following concerns of limited verbal and non-verbal communication, repetitive behaviors, rigidity around transitions, and extensive gastrointestinal symptoms, among other common symptoms. A parent-driven, multidisciplinary, therapeutic intervention involving a variety of licensed clinicians focusing primarily on addressing environmental and modifiable lifestyle factors was personalized to each of the twin’s symptoms, labs, and other outcome measures. Dramatic improvements were noted within several months in most domains of the twins’ symptoms, which manifested in reductions of Autism Treatment Evaluation Checklist (ATEC) scores from 76 to 32 in one of the twins and from 43 to 4 in the other twin. The improvement in symptoms and ATEC scores has remained relatively stable for six months at last assessment. While prospective studies are required, this case offers further encouraging evidence of ASD reversal through a personalized, multidisciplinary approach focusing predominantly on addressing modifiable environmental and lifestyle risk factors.

Adolescent leisure-time physical activity and eating disorders: a longitudinal population-based twin study

PurposeHigh levels of physical activity have been documented in eating disorder patients. Our aim was to examine whether adolescent leisure-time physical activity is prospectively associated with eating disorders in adolescence and young adulthood.MethodsFinnish twins born in 1983–1987 reported their physical activity frequency at ages 12, 14, and 17. A subsample of participants underwent structured, retrospective interviews for eating disorders at the mean age of 22.4 years. Associations between female twins’ physical activity and future eating disorders (571–683 twins/wave) were investigated with the Cox proportional hazards model. To illustrate the physical activity similarity of the co-twins in a twin pair, we used cross-tabulation of eating disorder–discordant twin pairs (13–24 pairs/wave).ResultsAfter adjusting for several covariates, we found no statistically significant longitudinal association between physical activity and eating disorders. This applied when all eating disorders were combined but also when assessed separately as restrictive and non-restrictive eating disorders. Co-twins’ physical activity in adolescence tended to be similar irrespective of their future eating disorder, supporting the results of the regression analysis.ConclusionWe observed no evidence of adolescent physical activity frequency being prospectively associated with eating disorders in female twins. Further longitudinal studies with larger sample sizes and more detailed physical activity data are needed.Level of evidence: III, evidence obtained from cohort or case–control analytic studies.

O03 Genetic impacts on the skin methylome

Abstract Introduction and aims DNA methylation at CpG dinucleotides is a dynamic epigenetic mechanism that has been linked to numerous skin phenotypes and diseases. Previous studies in blood show that a substantial proportion of the human DNA methylome exhibits evidence for genetic influence, and that 15–17% of narrow-sense methylation heritability is explained by genetic variants, or methylation quantitative trait loci (meQTLs). However, no genome-wide meQTL studies have previously been performed in skin. The primary purpose of this work was to identify the genetic basis of DNA methylation levels in whole skin. Methods Utilizing a twin-based heritability model, we estimated DNA methylation heritability using 414 bulk skin tissue samples from healthy older female twins from the TwinsUK cohort, profiled using the Illumina Infinium HumanMethylation450 BeadChip (Illumina, San Diego, CA, USA). We then integrated genomic data for 394 of these twins to perform genome-wide meQTL analyses. Finally, we integrated these meQTL Results with skin eQTL Results from an overlapping sample (N = 664). Results Over 8.2% of measured CpG sites showed evidence for strong heritability (h2 &amp;gt; 0.4), with a mean additive heritability estimate of 11.07% across all tested sites. We identified 76 442 CpG sites (18.8% of measured CpG sites) associated with a meQTL in cis (&amp;lt; 1 MB variant-CpG distance) and 1438 (0.35%) in trans. Both CpG sites under meQTL effects, and genetic variants underlying these meQTL effects in skin, are enriched in regions previously identified from genome-wide and epigenome-wide association studies for skin-related phenotypes, including psoriasis, melanoma and vitiligo. Additionally, some meQTLs influence gene expression via mediation of expression quantitative trait loci effects in skin, including in genes linked to melanoma and psoriasis. Conclusions Our study is the first genome-wide DNA methylation heritability and meQTL analysis of whole skin, giving insights into the regulatory landscape of epigenomic variation in skin.

Shifting goalposts: widening discrepancies between girls' actual and ideal bodies predict disordered eating from preadolescence to adulthood.

Little is known regarding how disordered eating (DE) relates to perceived actual body size, ideal body size, and their discrepancy. This study examined changes in perceived actual body size, ideal body size, and actual-ideal discrepancies over time, and their relationship with subsequent DE. Participants were 759 female twins from the Minnesota Twin Family Study who reported on body image and DE every three to five years between approximately ages 11 to 29. We used multilevel modeling to examine developmental trajectories of body mass index (BMI) and Body Rating Scale Actual, Ideal, and Actual-Ideal discrepancy scores and compared the degree to which BMI, BRS body size perceptions, and body dissatisfaction predicted DE behaviors and attitudes over time. Participants were treated as singletons in analyses. Perceived Actual body sizes and BMIs increased from age 10 to 33, whereas Ideal body sizes remained largely stable across time, resulting in growing Actual-Ideal discrepancies. Body size perceptions and Actual-Ideal discrepancies predicted subsequent DE behaviors and attitudes more strongly than did body dissatisfaction as measured by self-report questionnaires. This research advances understanding of how female body size perceptions and ideals change across development and highlights their relationship with subsequent DE.

Postmenopausal hormone therapy and cognition in twins

ObjectiveMild cognitive impairment may be caused by pathophysiological changes occurring decades prior to symptom development. It has been hypothesised that oestrogen can prevent such changes. We aimed to investigate the association between postmenopausal hormone therapy and cognition in Danish female twins and to examine differences in this association before and after publication of the findings from the Women’s Health Initiative study in 2002. Study designThis study includes cognitive assessment of 4510 twins aged 50+ years. Information on hormone therapy was obtained through Danish health registries. The association between current hormone therapy use and cognition was analysed in twins aged 50+ using both cross-sectional, intrapair and longitudinal analysis, adjusting for age, education, social class, and unobserved familial confounding. ResultsCross-sectionally, systemic HT users aged 70+ had a significantly lower cognitive function than non-users, whereas systemic HT users aged 50–69 did not differ from non-users before 2002.Longitudinal data in younger twins aged 50–69 showed a significantly lower cognitive function in systemic HT users after 2002 compared to non-users. Systemic HT users aged 70+ showed that the lower cognitive function was most explicit before 2002, whereas after 2002 the cognitive function was closer to non-users.Twins aged 50–69 who changed from systemic HT to local HT after 2002, or dropped it altogether, performed cognitively better. ConclusionsOur findings cautiously indicate a change in the association between cognition and hormone therapy use after 2002, which suggests an alteration in the hormone therapy user profile in the wake of the 2002 WHI publication.

77 Healing progression of tail docking and ear tag wound in lambs

Abstract Tail docking and ear tagging are common husbandry practices in lambs, but little is known about the healing process of the resulting wound. Additionally, evidence in other species shows that concurrent injurious procedures may delay wound healing. Thus, the objectives of this study were to 1) describe wound healing following tail docking and ear tagging, and 2) compare healing of ear tag wound in docked and undocked lambs. Within 28 Polypay female twin pairs, one lamb was docked by placing a constrictive rubber ring on the tail 24 to 48 h after birth and the tail of the other lamb was left intact (n = 28/treatment). Plastic-tipped ear tags were applied to both ears of all lambs immediately before tail docking. Wound photos of the ears and tail were taken twice weekly until weaning, resulting in 16 to 22 observations per lamb. Tail wound photos were analyzed to determine when the tail fell off and to score the presence of 6 tissue types: pus, serous exudate, sanguineous exudate, granulation, crust, and slough. A healed tail or ear wound was defined as one that was fully contracted, and no other tissue types were present. Tails took 19 ± 2 d to fall off (mean ± SD; range = 16 to 25 d) and their wound took 41 ± 8 d to heal completely (30 to 60 d). The prevalence of any of the 6 tissue types did not predict how long it took the tail wound to heal (F &amp;lt; 2.50, P &amp;gt; 0.13). Tissue types, indicative of possible infection, such as pus and slough, were present at least once in 89% and 93% of the docked lambs and in 8% and 10% of the total sampling periods, respectively. On average, pus and slough first appeared 12 ± 4 d (range = 5-22) and 11 ± 3 d (5-15) after docking, respectively. Of the 112 ear wounds, only 16% had healed by the time the lambs were weaned (55 to 74 d after tagging). Contrary to our predictions, there was a tendency for more docked lambs to have at least one healed ear wound by the end of the sampling period compared with undocked lambs (11 docked lambs vs 4 undocked lambs; X2 = 3.28, P = 0.07). This may be a result of an increased systemic inflammatory response and possible reduction in activity in the docked lambs. Overall, most ear tag wounds were still not healed after 2 mo, and tail wound took over 1 mo to heal. Further research is needed to determine the welfare implications of routine husbandry practices in sheep, including pain experienced during healing and how other factors may affect the healing process.

Comorbidity Between Internalizing Symptoms and Disordered Eating Is Primarily Driven by Genetic Influences on Emotion Regulation in Adult Female Twins

Internalizing (e.g., anxiety, depression) and disordered eating (DE; e.g., binge eating, dietary restraint) are highly comorbid, but the mechanisms underlying their comorbidity remain unknown. This was the first twin study to examine whether their co-occurrence may be driven by genetic and/or environmental influences on emotion regulation (ER; ability to modulate duration/intensity of emotions). Analyses included 688 adult female twins from the Michigan State University Twin Registry. Cholesky decomposition twin models showed that comorbidity between dimensionally modeled internalizing and DE was due to overlapping genetic ( r = .55; 69.3% of shared variance) and nonshared environmental influences ( r = .26; 30.7% of shared variance). When ER was added into the model, all genetic influences shared between internalizing and DE were attributable to ER, suggesting genetic influences on ER are the primary driver of comorbidity between internalizing and DE. Shared genes may shape affective processing, interoceptive sensitivity, or other brain-based processes (e.g., cognitive control) implicated in ER.

Bilateral Peters' anomaly, aniridia and Wilms tumour (WAGR syndrome) in monozygotic twins.

This study reports the bilateral association of Peters' anomaly and congenital aniridia in monozygotic twins subsequently diagnosed with Wilms tumour (WAGR syndrome). Two monozygotic female twins were referred at age 2 months with bilateral corneal opacity. A diagnosis of Peters' anomaly associated to aniridia was made in both eyes of both twins. Physical examination and ultrasonography were carried out at 12 months of age to explore the possibility of WAGR-related anomalies, specifically Wilms tumour. DNA were isolated and subjected to whole exome sequencing. Peters' anomaly associated to aniridia in both eyes as well as bilateral Wilms tumour in both children were diagnosed. Exome analyses showed a large heterozygous deletion encompassing 6 648 473 bp in chromosome 11p13, using Integrative Genomics Viewer and AnnotSV software. WAGR syndrome is a rare contiguous gene deletion syndrome with a greater risk of developing Wilms tumour associated with Peters' anomaly and congenital aniridia. However, co-occurrence of both anomalies was rarely reported in twins, and never in both eyes of monozygotic twins. Here, we report the bilateral association of Peters' anomaly and congenital aniridia in monozygotic twins with WAGR syndrome.

Familial congenital laryngotracheal stenosis: A systematic review

BackgroundCongenital laryngotracheal stenosis (CLS) is a rare cause of stridor among newborns. Evidence has shown that several family members can be affected by CLS. Knowledge of the pathophysiology of familial congenital laryngotracheal stenosis (FCLS) will enable more effective therapeutic strategies. ObjectiveTo determine the clinical course and outcome of familial congenital laryngotracheal stenosis (FCLS). MethodsA literature search was conducted over a period of one month (September 2023) by searching several databases to identify studies published from inception to 31st August 2023. ResultsOf 256 papers identified, five articles met the inclusion criteria. A total of 17 patients with slight female predominance (59 %) were identified. Familial congenital tracheal stenosis was reported in female twins (100 %). A variety of clinical presentations were listed. An endoscopic airway study was performed on all patients. 64.8 % of the included children were managed surgically. Genetic studies performed on 41 % of children could not locate genetic abnormalities. ConclusionConsanguinity, twin births, and female gender could be predisposing factors for FCLS, although the quality of evidence is low due to the rarity of the condition.

Fabry disease in female monozygotic twins with a complex intronic haplotype mutation: A case report

Fabry disease in female monozygotic twins with a complex intronic haplotype mutation: A case report

Diet patterns and cognitive performance in a UK Female Twin Registry (TwinsUK)

BackgroundPlant-based diets may provide protection against cognitive decline and Alzheimer’s disease, but observational data have not been consistent. Previous studies include early life confounding from socioeconomic conditions and genetics that are known to influence both cognitive performance and diet behaviour. This study investigated associations between Mediterranean (MED) diet and MIND diets and cognitive performance accounting for shared genotype and early-life environmental exposures in female twins.MethodsDiet scores were examined in 509 female twins enrolled in TwinsUK study. The Cambridge Neuropsychological Test Automated Battery was used to assess cognition at baseline and 10 years later (in n = 275). A co-twin case–control study for discordant monozygotic (MZ) twins examined effects of diet on cognitive performance independent of genetic factors. Differences in relative abundance of taxa at 10-year follow-up were explored in subsamples.ResultsEach 1-point increase in MIND or MED diet score was associated with 1.75 (95% CI: − 2.96, − 0.54, p = 0.005 and q = 0.11) and 1.67 (95% CI: − 2.71, − 0.65, p = 0.002 and q = 0.02) fewer respective errors in paired-associates learning. Within each MZ pair, the twin with the high diet score had better preservation in spatial span especially for MED diet (p = 0.02). There were no differences between diet scores and 10-year change in the other cognitive tests. MIND diet adherence was associated with higher relative abundance of Ruminococcaceae UCG-010 (0.30% (95% CI 0.17, 0.62), q = 0.05) which was also associated with less decline in global cognition over 10 years (0.22 (95% CI 0.06, 0.39), p = 0.01).ConclusionsMIND or MED diets could help to preserve some cognitive abilities in midlife, particularly episodic and visuospatial working memory. Effects may be mediated by high dietary fibre content and increased abundance of short-chain fatty acid producing gut bacteria. Longer follow-up with repeated measures of cognition will determine whether diet can influence changes in cognition occurring in older age.

Technical strategy for monozygotic twin discrimination by single-nucleotide variants.

Monozygotic (MZ) twins are theoretically genetically identical. Although they are revealed to accumulate mutations after the zygote splits, discriminating between twin genomes remains a formidable challenge in the field of forensic genetics. Single-nucleotide variants (SNVs) are responsible for a substantial portion of genetic variation, thus potentially serving as promising biomarkers for the identification of MZ twins. In this study, we sequenced the whole genome of a pair of female MZ twins when they were 27 and 33years old to approximately 30 × coverage using peripheral blood on an Illumina NovaSeq 6000 Sequencing System. Potentially discordant SNVs supported by whole-genome sequencing were validated extensively by amplicon-based targeted deep sequencing and Sanger sequencing. In total, we found nine bona fide post-twinning SNVs, all of which were identified in the younger genomes and found in the older genomes. None of the SNVs occurred within coding exons, three of which were observed in introns, supported by whole-exome sequencing results. A double-blind test was employed, and the reliability of MZ twin discrimination by discordant SNVs was endorsed. All SNVs were successfully detected when input DNA amounts decreased to 0.25ng, and reliable detection was limited to seven SNVs below 0.075ng input. This comprehensive analysis confirms that SNVs could serve as cost-effective biomarkers for MZ twin discrimination.

Monozygotic twin sisters differ in voice quality: Acoustic analysis of the diphthong [‘oj] produced by Brazilian native speakers

Identical twins challenge individual voice recognition applied in communication, criminal investigation, and health technologies. The similarities between siblings are due to the genetic heritage that produced either their vocal tract or the psychological processes acting since birth. To contribute to a precise individual identification by voice, we tested the hypothesis that even MZ siblings would differ in the spectral distribution of formants and sound quality. We recorded 86 same-sex twin pairs (71 MZ, 15 DZ 30 ± 12 years old) saying the Portuguese verse of “Hi, my name is (Pedro or Ana).” We trimmed the diphthong Ój (“Hi”) and measured f0, F1-F4 formants, jitter, shimmer, and Harmonic-to-noise ratio (HNR). As the male sampling was small, we compared only female twins using the Wilcoxon-matched test, the intrapair Correlation Coefficient (ICC), and GLMM models. On average, [Ój] lasted 0.24 ± 0.07 s, and f0 ranged from 469 to 510 kHz according to sex. We found no differences between the MZ or DZ sisters in any acoustic parameter, besides F1 for MZ ones. Also, MZ sisters were more alike (F1, jitter, HNR, weak; F3, F4 moderate) than DZ (only F1 high ICC). The interaction zygosity × age affected intrapair similarity, the older the sisters, the greater their differences. Short voice segments, like the diphthong [Ój], may not be good for differentiating identical twins but provide insights to discussion; F2, F4, and shimmer should be investigated in future studies considering males, younger participants, and other vocal expressions.