The clinical phenotypes of PWS vary greatly with age. During the early period after birth, the motor performance is particularly affected in infants with PWS. Most cases present as severely hypotonic, inactive and sometimes almost motionless in the neonatal period. Despite the fact that they persistently suffer from hypotonia, muscle weakness, and severe motor development delays, the young infants with PWS gradually become more responsive and present more spontaneous movements weeks or months later [6, 28]. Motor problems occur after birth and continue into adulthood for the rest of their lives. PWS patients scored well below the normal standard range on standardized motor performance tests . Holm VA was the first to propose the PWS clinical scoring diagnosis system based on the characteristics of the clinical symptoms in 1993. This system subdivided and summarized each clinical manifestation by score according to age, realizing the clinical standardized diagnosis of PWS. For newborn infants with obvious hypotonia, difficulty feeding and gonadal dysplasia, the possibility of PWS should be suspected . However, in terms of the method of carrying out a standardized quantitative assessment of the motor performance particularly in individuals with suspected PWS or infants that were diagnosed with PWS at a young age (less than 6 months old), there is still a lack of relevant research in this field so far.
It is extremely difficult to carry out prospective behavioural analyses of rare disorders . However, GMs assessment (video recording assessment) has been applied to early screening and assessment in genetic metabolic diseases . Christa Einspieler with her colleagues conducted a longitudinal study on the predictive value of movements and postures for infants with Smith-Magenis syndrome on the development of neurological deficits later in life. The findings, which were significantly reduced motor repertoire, absent fidgety general movements, abnormal posture and jerky and monotonous overall movements, indicate a severe motor impairment by no more than 4 months of age . Similar results have been shown in other genetic metabolic disorders, where the infants with the most severe phenotypes show no fidgety movements when aged 3–5 months, while their neurodevelopmental status was found to be more or less normal otherwise [12, 32–33]. Until now, there has been little systematic data on the early neurodevelopmental functioning of infants with PWS, and this study will be as the basis of preliminary research to document a behavioural manifestation of the syndrome as early as 4 months of age by assessment of Motor Repertoire -3 to 5 Months. The absence of fidgety movements and the presence of characteristic clinical phenotype indicate a risk of maldevelopment. Therefore, genetic testing and early rehabilitation intervention are reasonable recommendations. Early rehabilitation intervention plays a positive role in promoting infant development and improving developmental outcomes.
In this reliability study of the detailed general movements assessment (Assessment of Motor Repertoire-3 to 5 Months), we have obtained the following results: (1) Three observers who are qualified members of the GMs Trust participated in the assessment of video recordings of spontaneous movements for infants with PWS. The overall reliability ICCs values of MOS ranged from 0.84 to 0.98 in three observers, which indicate that the agreement reliability among raters reached a very high degree. ICC values for MOS ranged between 0.83 and 0.95 for pairwise agreement in inter- observer reliability where the highest ICC value of A-C was 0.95(95%CI 0.85-0.98), followed by B-C where the ICC value was 0.89(95%CI 0.67-0.96), and the ICC value was 0.86(95%CI 0.88-0.95) for A-B. ICC values ranged between 0.95 and 0.98 for the Intra-tester reliability of the MOS between the first and the second rating time-point in observers. Therefore, in the PWS population, MOS has very good interobserver reliability and retest reliability, which can be applied very well in the clinical quantitative evaluation of the early motor performance for infants with PWS. (2) The subcategory “Fidgety Movements” in the “Assessment of Motor Repertoire-3 to 5 Months” was divided into three subtypes: normal fidgety movements (12 scores), abnormal fidgety movements (4 scores) and absent fidgety movements (1 scores). The assessment results of all observers (A-C) were completely consistent with that of absent fidgety movements(1 scores)based on the severely hypotonic, inactive and sometimes almost motionless infants with PWS in the neonatal period seen in this study. Because Kappa statistical analysis is based on multicategorical variables, the Kappa value cannot be calculated with a single variable for the outcome of absent fidgety movements in this study. Therefore, the percentage of agreement represented the detailed impression of the degree of the reliability and agreement in the subcategory “Fidgety Movements”. The complete agreement reliability (100%) was achieved in both the interobservers reliability (A-B, A-C, B-C) and the re-tests reliability of the observers (A-C) in this study. Inter-and intra-observer reliability in the subcategory “Movement Character” in the “Assessment of Motor Repertoire-3 to 5 Months” was exactly the same as the reliability of “Fidgety Movements”. (3) The points achieved in the subcategories“Quality of Other Movements”and “Posture were calculated based on the sum of the number of normal and abnormal items in their respective category entries. Accordingly, the result was not simply based on the inter- and intra-observer agreement in each item, even if agreement reliability values on each item of these subcategories were analyzed to be low, which didn't necessarily affect the MOS and ultimately the ICC values of reliability. Moderate to high inter-observer reliability were achieved in the assessment of “Quality of Other Movements” among observers (A-B, A-C, B-C), with kappa values ranging between 0.66 and 0.77. The assessment of “Posture” resulted in very good kappa values in pairwise inter- observer agreement (A-B, A-C, B-C), and the total of the kappa values was 1.00. Moderate to high intra-observer reliability was achieved in the assessment of “Quality of Other Movements” (A, B, C), and “Posture” (A, C) with kappa values ranging between 0.63 and 1.00. The complete agreement reliability (100%) was achieved in the re-test reliability of “Posture” for observer B.
Compared with previous studies in genetic metabolic disorders, the reliability study of detailed GMs assessment for Smith-Magenis syndrome for inter-observer agreement indicated Kappa values between 0.82 (assessment of posture) and 1.00 (assessment of fidgety movements) and is similar to the research results of these two parts in this study . In the reliability study of high risk infants, inter-observer reliability in the assessment of the total MOS was high between observers as ICC was 0.87, and ICCs for the pairwise analyses ranged between 0.80 and 0.94, which is consistent with the results of this study . However, the agreement reliability regarding the subcategory “Postures” and “Movement Character” in this study was better than that of infants with a high risk of brain injury, in which the “Movement Character” kappa was 0.54-0.84 and the “Posture” kappa was 0.39-0.56.
In this study, the “Assessment of Motor Repertoire-3 to 5 Months” in infants with PWS we have high reliability in inter-and intra-observers, which is not only related to the characteristics of early motor performance in infants with PWS, but also has a great correlation with the following factors: (1)Video acquisition process requires strict regulations to ensure high quality assessment of video recordings, which plays an important role in the accuracy of GMs assessment results based on Gestalt perception theory. (2) Three observers had completed the advanced training courses of GMs and had a rich experience in GMs assessment in clinical practice. In addition, we hold a GMs assessment quality control meeting once a week to discuss difficult GMs cases and the standardized assessment process. All of these clinical practices help to greatly improve the accuracy and consistency of the GMs assessment results among observers.
Of course, there are also some limitations in this study. On the one hand, the population characteristics of PWS are less representative in this study. More than 90% of the infants with PWS were of the “Total Optimality Score” under 9 points and the sample size is also very limited in this study. On the other hand, the assessment results were completely consistent with that of absent fidgety movements(1 scores)for infants with PWS in this study. Thus, the assessment of “Fidgety Movements”, which itself showed good inter-observer agreement, had a significant effect on the ICCs for the total MOS. Therefore, the sample size and study units should be increased in later studies to reduce research bias.