The research, led by Oguzhan Ekizoglu together with Marine Dario, Maxime Pastor, Catherine Cyteval, and Laurent Martrille, focused on a bone that has been comparatively neglected in the MRI-based age estimation literature: the proximal humerus, the ball-shaped top of the upper arm bone. While the hand-wrist region and the knee have been extensively mapped with MRI for forensic purposes, the shoulder has received far less systematic attention, particularly in Western European populations. The team retrospectively analyzed 346 shoulder MRI examinations drawn from a French cohort spanning the ages of 7.18 to 33.82 years, comprising 204 males and 142 females. Because the scans had been acquired for clinical reasons and were fully anonymized, the ethics committee of CHU Montpellier approved the study and waived the need for individual informed consent, an approach consistent with the Declaration of Helsinki.

The technical backbone of the study is the combined Schmeling–Kellinghaus staging system, a widely used framework originally developed for the medial end of the collarbone. In this system, ossification of the epiphysis, the secondary growth center that fuses to the main bone shaft after puberty, is graded in discrete stages, from an entirely cartilaginous growth plate through progressive partial fusion to complete union, with an optional subdivision for the earliest signs of fusion. On T1-weighted MRI sequences, the developing bone and the cartilaginous plate between epiphysis and metaphysis produce distinct signal intensities, allowing a trained observer to assign each shoulder to a stage. Two independent raters, blinded to each subject’s age and sex, staged all 346 scans, providing a direct test of how reproducible the method is when applied to the humeral head.

The results were strikingly consistent. The correlation between chronological age and ossification stage was strong and statistically significant across the whole sample, with a Spearman’s rank correlation coefficient of 0.878, and nearly identical values of 0.880 in males and 0.878 in females, all with p-values below 0.001. In practical terms, this means that as the humeral epiphysis progresses through its developmental stages, age increases in a tight, predictable relationship, and that this relationship holds equally well for both sexes. Statistical testing with the Mann–Whitney U method found no significant difference between males and females in the ages associated with any given stage, a finding that simplifies the application of the system, since a single set of stage descriptions may suffice for both sexes in this population.

Reliability, the measure of whether different observers reach the same conclusion from the same image, was equally impressive. Cohen’s kappa, a statistic that quantifies agreement beyond what would be expected by chance, reached 0.911 within observers rating their own scans twice and 0.890 between the two independent raters. Values above 0.8 are conventionally considered to indicate very good agreement, and these figures place the proximal humerus staging on par with, or better than, many established forensic imaging indicators. For a method that might one day inform legal decisions with life-changing consequences, this level of observer agreement is not a technical nicety but an essential prerequisite, because inconsistent readings between experts would undermine the credibility of any age estimate offered in court.

The most legally consequential finding concerns the age of majority, the threshold at 18 years that separates minors from adults in most jurisdictions. In this cohort, the youngest individual showing stage 4, defined by the presence of a visible epiphyseal scar after fusion, was 18.33 years in males and 18.06 years in females. In other words, once the epiphyseal scar is visible on the proximal humerus, the data suggest the person has very likely passed their eighteenth birthday. Notably, stage 5, the final stage of the amplified scheme, was never observed despite the cohort including individuals up to nearly 34 years of age, an observation the authors interpret in light of the persistent visibility of the epiphyseal scar in adult shoulders and the anatomical characteristics of trabecular bone in this region.

Beyond the conventional minimum-age approach, the team applied an ordinal probit transition analysis, a statistical framework borrowed from paleodemography that models the probability of moving from one ossification stage to the next as a function of age. Rather than relying on the single youngest individual observed at a stage, a figure that is highly sensitive to how many older or younger people happen to be in the sample, transition analysis yields sex-specific ages at which the probability of progression to the next stage reaches 50 percent. This provides a more statistically robust characterization of the timing of skeletal maturation and has been increasingly advocated in forensic age research, including recent work on third molars and other skeletal indicators. The authors are careful, however, to stress that both minimum-age and transition-age estimates derived from any single cohort should not be applied as forensic thresholds without independent, population-specific validation, a caution that reflects the well-documented variation in skeletal maturation across populations and socioeconomic conditions.

Perhaps the most original contribution of the study is the description of a previously unreported interpretive pitfall. The authors identified a trabecular hypointense pattern, a dark appearance of the internal bone architecture on T1-weighted images, that can potentially mimic a persistent gap between the epiphysis and the metaphysis, the appearance that would normally indicate an unfused, and therefore juvenile, growth plate. Mistaking this normal variant for an open growth plate could lead an examiner to underestimate a person’s age, with serious implications in asylum or criminal proceedings. The paper includes recommendations for recognizing this pattern, underscoring that even a highly reliable staging system depends on the examiner’s ability to distinguish true developmental landmarks from imaging artifacts and anatomical variants of the cancellous bone in the proximal humerus.

The broader context of this work is a slow but decisive shift in forensic practice. European radiation protection directives and international basic safety standards from bodies such as the International Atomic Energy Agency have sharpened the ethical and legal scrutiny applied to X-ray-based age assessments in healthy young people, pushing researchers toward MRI as a non-ionizing alternative. Previous MRI studies of the proximal humeral epiphysis, including earlier work by Ekizoglu and colleagues on Turkish cohorts and studies from China and Turkey using both 1.5 and 3.0 Tesla scanners, have demonstrated the promise of the approach, but population-specific data remained sparse for Western Europe. By extending the combined Schmeling–Kellinghaus system to a French cohort for the first time, the Montpellier team has filled an important geographic gap and shown that the staging framework travels well across populations, at least in terms of correlation strength and observer reliability.

What remains before shoulder MRI can enter routine forensic use is a matter of validation and standardization rather than proof of concept. Large, independently collected cohorts from different populations will be needed to confirm the minimum ages and transition probabilities reported here, and the newly described trabecular pitfall will need to be characterized across scanner types and imaging protocols. Cost and scanner availability also remain practical constraints, since MRI is more expensive and less widely accessible than plain radiography. Nevertheless, the study offers a compelling vision of the field’s future: a radiation-free, highly reproducible, and anatomically well-characterized method for answering one of forensic science’s most sensitive questions. For the hundreds of thousands of young people whose ages are contested each year in legal systems worldwide, the humeral head, imaged safely with magnets rather than X-rays, may soon become a key witness.

Subject of Research: Non-ionizing forensic age estimation using T1-weighted MRI of the proximal humeral epiphysis in a French cohort

Article Title: T1-Weighted MRI of the proximal humerus: Toward a non-ionizing approach to forensic age estimation in a French cohort

Article References: Ekizoglu, O., Dario, M., Pastor, M., Cyteval, C., & Martrille, L. (2026). T1-Weighted MRI of the proximal humerus: Toward a non-ionizing approach to forensic age estimation in a French cohort. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-03996-7

Image Credits: AI Generated

DOI: 10.1007/s00414-026-03996-7

Keywords: forensic age estimation, MRI, proximal humerus, epiphyseal fusion, Schmeling-Kellinghaus staging, age of majority, transition analysis, non-ionizing imaging, forensic medicine, immigration, radiation protection, French cohort

Retinitis pigmentosa, also known as rod-cone dystrophy, is one of the most genetically heterogeneous disorders in human medicine. It begins with the progressive loss of rod photoreceptors, the cells responsible for vision in dim light, which produces night blindness and narrowing of the visual field. As the disease advances, cone photoreceptors, which mediate daylight and color vision, degenerate as well, often culminating in severe visual impairment or legal blindness in midlife. Approximately forty genes have so far been linked to the autosomal dominant form of the disease, in which a single inherited copy of a pathogenic variant is sufficient to cause symptoms. Yet even with modern genetic testing, a stubborn fraction of patients never receives a molecular diagnosis.

That diagnostic gap was precisely what motivated the new study. The researchers, led by Isabelle Audo and Christina Zeitz of Sorbonne Université, INSERM, CNRS and the Institut de la Vision in Paris, together with colleagues at the Centre Hospitalier National d’Ophtalmologie des Quinze-Vingts and partner institutions, analyzed a French cohort of 395 families with autosomal dominant retinitis pigmentosa and 418 genetically unsolved cases. Every participant underwent comprehensive ophthalmic examination, including standard-of-care retinal imaging and functional assessments, ensuring that the genetic findings could be interpreted against detailed clinical pictures. The team combined genome sequencing, direct Sanger sequencing and a candidate gene approach to interrogate regions of the genome that standard analyses often skip.

The regions they targeted belong to a family of genes with an unusual biology. Small nuclear RNA genes do not encode proteins; instead, they produce short RNA molecules that form the structural and catalytic core of the spliceosome, the cellular machine that removes intervening sequences from messenger RNA precursors. The U4 and U6 small nuclear RNAs associate with U5 snRNA and a set of proteins to build the tri-small nuclear ribonucleoprotein complex, or tri-snRNP, a central component of the major spliceosome. Because splicing is essential in every cell, one might expect defects in these genes to be lethal or to cause widespread damage. Instead, recent years have revealed a striking pattern: inherited and de novo variants in snRNA genes appear in people with recessive neurodevelopmental disorders, and, as the new work confirms, in people with inherited retinal degeneration.

What makes the retinal findings particularly intriguing is where the disease-causing variants sit within these small RNA genes. The variants associated with retinitis pigmentosa cluster in regions that are distinct from those implicated in neurodevelopmental disorders, and they affect domains involved in the assembly of the tri-snRNP with three proteins that retinitis specialists know well: PRPF3, PRPF8 and PRPF31. All three of these proteins are themselves established causes of autosomal dominant retinitis pigmentosa. In other words, the retina appears to be exquisitely sensitive to a specific kind of disruption in the splicing machinery, one that interferes with the assembly of the tri-snRNP complex, while other tissues tolerate it. This convergence of RNA genes and spliceosome protein genes on the same disease phenotype provides a coherent mechanistic thread through what had seemed like scattered genetic findings.

The results of the cohort screen were unambiguous. The researchers identified heterozygous inherited variants in RNU4-2 and in RNU6 paralogs in eight unrelated families with non-syndromic autosomal dominant retinitis pigmentosa. In every family where additional members were available for testing, the variant co-segregated with the disease, passing from affected parents to affected children exactly as an autosomal dominant mutation should. None of the affected individuals showed the extra-neurological features that might suggest a syndromal diagnosis; their disease was confined to the retina, reinforcing the idea that these snRNA variants produce a pure retinal phenotype rather than a broader developmental syndrome.

Translated into population terms, the eight families mean that variants in RNU4-2 or RNU6 paralogs account for two percent of the genetically solved individuals with autosomal dominant retinitis pigmentosa in the cohort. Perhaps more striking is the comparison the authors draw within the spliceosome category: these snRNA variants represent six percent of all individuals carrying variants in genes coding for the multi-subunit spliceosome complex. A single family of non-coding RNA genes therefore contributes a non-trivial share of the spliceosome-related disease burden, a category that until now has been defined almost entirely by protein-coding genes such as PRPF31, PRPF8, PRPF3, PRPF4, PRPF6, SNRNP200 and RP9. The message for diagnostics is clear: excluding snRNA genes from analysis leaves a measurable fraction of patients without answers.

Why have these genes escaped detection for so long? The answer lies partly in the mechanics of genome analysis. Small nuclear RNA genes are short, repetitive and often present in multiple copies or paralogs scattered across the genome, which complicates the alignment of sequencing reads and the confident calling of variants. Many bioinformatics pipelines are tuned to detect single nucleotide changes in protein-coding exons and simply do not report variants in these loci, even when the underlying sequence data contain them. The French team’s use of genome sequencing combined with targeted Sanger validation illustrates the practical path forward: once a candidate snRNA variant is flagged, conventional sequencing can confirm it and family studies can establish segregation. The bottleneck is not the technology but the willingness to look in places the standard tools ignore.

The clinical implications extend beyond diagnosis. A confirmed molecular diagnosis is the gateway to genetic counseling, allowing affected individuals to understand the inheritance pattern and recurrence risk in their families, and to reproductive options such as preimplantation genetic testing. It is also increasingly the entry ticket to precision therapy, as gene-specific clinical trials for inherited retinal disease multiply. For the two percent of autosomal dominant retinitis pigmentosa patients who carry RNU4-2 or RNU6 paralog variants, inclusion of snRNA genes in diagnostic panels could mean the difference between an unsolved case and eligibility for emerging interventions. The finding also suggests that other unexplained retinal degenerations might owe their existence to additional non-coding RNA genes waiting to be interrogated.

Scientifically, the study strengthens an emerging view of the spliceosome as a hotspot for tissue-specific disease. The retina, with its extraordinarily high metabolic demands and its photoreceptors’ constant need to renew outer segment proteins, appears uniquely vulnerable to partial defects in RNA processing that other tissues can buffer. The clustering of retinal disease variants in tri-snRNP assembly domains, distinct from the regions implicated in neurodevelopmental disorders, hints at a genotype-phenotype map within molecules barely a hundred nucleotides long. As genome sequencing becomes the default first test for rare disease, the French cohort results argue that the small RNAs at the heart of the spliceosome deserve a permanent place on the diagnostic checklist, both for the patients they will finally explain and for the biology they continue to reveal.

Subject of Research: Small nuclear RNA gene variants causing autosomal dominant retinitis pigmentosa

Article Title: Variants in RNU4-2 or RNU6 paralogs account for 2% of individuals with non-syndromic autosomal dominant retinitis pigmentosa in a large French cohort

Article References: Audo, I., Navarro, J., Bianco, L., Antropoli, A., Condroyer, C., Antonio, A., Andrieu, C., Mohand-Saïd, S., Laurent-Coriat, C., Atia, R., Benadji, A., Smirnov, V., Sahel, J.-A., & Zeitz, C. (2026). Variants in RNU4-2 or RNU6 paralogs account for 2% of individuals with non-syndromic autosomal dominant retinitis pigmentosa in a large French cohort. Genome Medicine. https://doi.org/10.1186/s13073-026-01743-6

Image Credits: AI Generated

DOI: 10.1186/s13073-026-01743-6

Keywords: retinitis pigmentosa, RNU4-2, RNU6, small nuclear RNA, spliceosome, tri-snRNP, inherited retinal disease, genome sequencing, autosomal dominant inheritance, RNA splicing, genetic diagnosis, French cohort