Genotype-Phenotype Correlation in Neurofibromatosis Type 1: Evidence for a Mild Phenotype Associated with Splicing Variants Leading to In-Frame Skipping of NF1 Exon 24 [19a].

Neurofibromatosis type 1 (NF1) is an autosomal dominant neurocutaneous disorder caused by loss-of-function variants in the NF1 gene. As of 20 November 2023, over 5000 distinct pathogenic or likely pathogenic variants have been reported in public databases. However, only a few NF1 genotype-phenotype correlations have been established so far. In this study, we present findings on 40 individuals with NF1, comprising 26 unrelated probands and 14 affected relatives, who carry one of nine NF1 heterozygous pathogenic splicing variants, all of which result in the in-frame skipping of exon 24 [19a] (NM_000267.3:r.3114_3197del, p.Asn1039_Arg1066del). These variants include c.3114-2A>G, c.3114-1G>A, c.3196A>G, c.3197G>A, c.3197G>T, c.3197+1G>A, c.3197+1G>T, c.3197+2T>C, and c.3197+3A>T. Among individuals with these variants, none exhibit externally visible plexiform neurofibromas, histopathologically confirmed cutaneous or subcutaneous neurofibromas, symptomatic spinal neurofibromas, or symptomatic optic pathway gliomas. The most prevalent, and sometimes sole, clinical feature observed in this cohort is multiple café-au-lait macules, with or without skinfold freckles: 85% and 60.5% of the individuals display six or more café-au-lait macules and freckles, respectively. In comparison to established NF1 genotype-phenotype correlations, these patients demonstrate highly similar clinical presentations to those associated with the NF1 pathogenic variant c.2970_2972del (p.Met992del), known for resulting in the mildest clinical features. Despite the generally mild phenotype, cognitive impairment, developmental delay, and/or learning difficulties are still observed in 33.3% of these patients, suggesting that learning challenges remain a prominent aspect of the phenotypic presentation in these individuals and necessitate specialized care. This newly established genotype-phenotype correlation will assist clinicians in improving the management of patients harboring NF1 exon 24 [19a] skipping variants and provide a new therapeutic target for NF1 treatment.

Neurofibromatosis- and schwannomatosis-associated tumors: Approaches to genetic testing and counseling considerations.

Neurofibromatosis (NF) and schwannomatosis (SWN) are genetic conditions characterized by the risk of developing nervous system tumors. Recently revised diagnostic criteria include the addition of genetic testing to confirm a pathogenic variant, as well as to detect the presence of mosaicism. Therefore, the use and interpretation of both germline and tumor-based testing have increasing importance in the diagnostic approach, treatment decisions, and risk stratification of these conditions. This focused review discusses approaches to genetic testing of NF- and SWN-related tumor types, which are somewhat rare and perhaps lesser known to non-specialized clinicians. These include gastrointestinal stromal tumors, breast cancer, plexiform neurofibromas with or without transformation to malignant peripheral nerve sheath tumors, gliomas, and schwannomas, and emphasizes the need for inclusion of genetic providers in patient care and appropriate pre- and post-test education, genetic counseling, and focused evaluation by a medical geneticist or other healthcare provider familiar with clinical manifestations of these disorders.

A novel manual therapy technique is effective for short-term increases in tibial internal rotation range of motion.

The coupled motions of tibial internal rotation (T-IR) and ankle dorsiflexion (DF) are necessary for proper lower-limb function. Anecdotally, clinicians have been performing techniques to restore T-IR to improve ankle DF, however, no evidence exists to support their efficacy. Therefore, the two objectives were to: (a) determine the effectiveness of a manual therapy technique for improving T-IR range of motion (ROM) and (b) Examine the relationship between ankle DF and T-IR ROM. Twenty-four participants qualified to participate and were randomly allocated to either the control (n=12) or manual therapy (n=12) group. Closed-chain ankle DF and T-IR ROM were assessed at baseline and immediately posttreatment. Control group participants sat quietly for 5 minutes. The experimental group performed 3 sets of 15 repetitions of a manual therapy, mobilization with movement technique. With the patient in a kneeling lunge position, the examiner wrapped an elastic band around the tibia and fibula and was instructed to lunge forward while the examiner simultaneously manually internally rotated the lower leg. T-IR ROM significantly increased following the intervention for the manual therapy group when compared to the control group. There were no significant changes in standing or kneeling DF ROM. No significant correlation was found between T-IR and both standing and kneeling DF ROM. A single mobilization with movement treatment is effective for improving tibial IR ROM in the short-term compared to no treatment. However, active tibial IR and end-range dorsiflexion range of motion do not appear to be correlated based on these methods.

The Rb1 gene inhibits the viability of retinoblastoma cells by regulating homologous recombination.

Retinoblastoma is a childhood ocular tumor caused by the inactivation of both alleles of the retinoblastoma gene (Rb1). Without Rb1 gene function, chromosomal aberrations are observed in retinoblastoma cells. The instability of the genome is closely associated with the repair of DNA double-strand breaks (DSBs). However, the precise molecular mechanism of action of Rb1 in DNA DSB repair remains unclear. Thus, in this study, we aimed to investigate whether the Rb1 gene affects DNA stability by assaying DNA DSB repair and also whether it regulates the proliferation of retinoblastoma cells. Rb1 immunofluorescence and RT-PCR were performed, demonstrating that the Rb1 gene is silenced in SO-Rb50 retinoblastoma cells, and the karyotype analysis of SO-Rb50 cells indicated that the loss of Rb1 function led to genomic instability; both numerical and structural chromosomal aberrations were observed in our study. In addition, the DNA DSB repair efficiency of the SO-Rb50 cells was measured by γ-H2AX immunofluorescence, a commonly used in situ marker of DNA DSBs, following exposure to ionizing radiation (IR) (2.5 and 5.0 Gy). We found that the DNA repair efficiency was significantly increased following IR-induced damage (P<0.01). However, there was no significant difference in DNA repair efficiency between the cells expressing exogenous Rb1 and the control (P>0.05). The assay for the screening of the effect of Rb1 on the sub-pathway of DNA DSB repair, non-homologous end joining (NHEJ) and homologous recombination (HR), indicated that Rb1 did not affect NHEJ activity, although it significantly promoted the HR pathway (HR levels increased by 2.46-fold) compared with the control (P<0.01). Furthermore, we found that the cell viability of the SO-Rb50 cells transfected with exogenous Rb1 was significantly inhibited (P<0.01) and cell cycle assay indicated that exogenous Rb1 induced S phase arrest (P<0.001) which also inhibited the proliferation of retinoblastoma cells (SO-Rb50) in vitro. Therefore, this study provides new insight into the mechanisms of action of the Rb1 gene in regulating the proliferation of retinoblastoma cells.

Spirometry and respiratory muscle function during ascent to higher altitudes.

Alteration in lung function at high altitude influences exercise capacity, worsens hypoxia, and may predispose to high-altitude illness. The effect of high altitude on lung function and mechanisms responsible for these alterations remain unclear. Seven adult male mountaineers were followed prospectively during a climbing expedition to Mount Everest, Nepal. Measurements of spirometry and respiratory muscle function were performed for the duration of the expedition, during changes in altitude between 3450 and 7200 meters (m). Measurements included the forced vital capacity (FVC), forced expiratory volume in 1 second (FEV(1)), maximal voluntary ventilation (MVV) in 12 seconds, maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), and respiratory muscle endurance (Tlim). At an altitude of 3450 m, the FVC initially increased (9%) over 24 h, followed by a significant decline; the FEV(1), MVV, MIP, and MEP showed similar progressive decline. At 5350 m, FVC increased by 21% over the first 48 h, then decreased. The FVC, FEV(1), MVV, MIP, and MEP initially increased and then gradually diminished over time. Respiratory muscle endurance (Tlim) decreased over the first three days at 3450 m but then remained unchanged. MVV decreased at lower altitude followed by a slight increase and then a significant decline. Compared with baseline, we observed a fluctuating course for spirometric measurements, respiratory muscle strength, and endurance at high altitude. Initial transient increases in parameters occurred on ascent to each new altitude followed by a gradual decline during prolonged stay.

The effect of drinking tea at high altitude on hydration status and mood.

The effect of drinking tea on hydration status and mood was studied in nine male and four female members of expeditions based at Mt. Everest base camp at an altitude of 5,345 m. Whilst exposed to altitude-cold diuresis, participants were subjected to a crossover experimental design comprising two 24-h dietary interventions. In the "tea" condition, hot brewed tea formed a major part of fluid intake, whereas in the "no-tea" condition tea was excluded from the diet. Subjects were prohibited in both cases from consuming other caffeinated beverages, caffeinated foods, and alcoholic drinks. Mean fluids ingested [mean (SE); tea=3,193 (259) ml versus no tea=3,108 (269) ml] and urine volume (tea=2,686 (276) ml versus no tea=2,625 (342) ml] were similar under both conditions. Statistical analysis found no difference in urine stimulated as a result of the tea intervention (P=0.81). Several markers of hydration status were also taken immediately pre and post each condition, including measures of urine specific gravity, urine electrolyte balance (K+, Na+), and urine colour. None of these measures indicated a difference in hydration status as a result of the dietary intervention in either the control or tea condition. A difference was, however, found in mood, with subjects reporting reduced fatigue when tea was included in the diet (P=0.005). The study shows therefore that even when drunk at high altitude where fluid balance is stressed, there is no evidence that tea acts as a diuretic when consumed through natural routes of ingestion by regular tea drinkers, but that it does have a positive effect on mood.