In this study, we analyzed the motor and ambulatory status, diagnosis method, and genetic profile of 152 DMD patients in Iran retrospectively.
An analysis of the natural history of DMD in Iran showed about 12 months diagnostic delay. Most DMD cases in our study reported their disease onset by 4.04 years of age, whereas the age of confirmed diagnosis by the molecular study was at 5.05 years old. Studies in other countries had also published a long delay in DMD diagnosis. The most important ground was the delay caused by parents with considering the delay in reports of first noticing symptoms, thereinafter delay to visit a doctor, or refer to the medical center. Several studies have recommended raising public awareness and alertness of initial symptoms related to DMD. Moreover, doing other evaluations and the second genetic study in patients with the first negative molecular study was time-consuming. Motor delay reported by parents was in 47.7% of our patients which is compatible with other studies (Wang et al. 2017, Vengalil et al. 2017). LOA happened in 42.7% of patients and the mean age of LOA and wheelchair dependency was 10.9 years which is consistent with some previous reports (Desguerre et al. 2009, Liang et al. 2018, Magri et al. 2011).
Although in the UK NorthStar database study and other researches LOA median age mentioned 13-year-old (Ricotti et al. 2016, Muntoni et al. 2019). The contracture was seen in 38.9 % and progressive weakness in 86.2%.
In the current study, we have addressed a number of important issues regarding the progression pattern of disease and describe the effect of age on its progression by linear format NSAA scale. To characterize the disease on linearized NSAA, we report the course of DMD in 152 Iranian boys.
We report the slope of progression after age 4 when the motor function starts to decline. With an average linearized NSAA score of 24 at age 4 years, we detected that the all-inclusive rate of decline on the linearized NSAA scale is 1.87 units/ year. These findings were coextensive with parents’ reports of disease onset age in our study. Whereas, previous studies on the age of NSAA score peak showed later age at 6 to 7 years but the maximum NSAA score was near our report as 26-row scores. We should emphasize that in these two study LOA occurred at 13 years while our patient’s LOA age was 10.9 years.
Therefore, the linearized NSAA can accurately support clinical trials to report outcome measures in the ambulant DMD population, and further, it simplifies the interpretation of possible outcomes in DMD ambulant boys who may lose ambulation during the study. We hope to provide more information about the motor natural history of Iranian DMD patients through our database that can be helpful to the design of potential DMD therapeutic trials.
Our study also revealed the mutational spectrum of DMD patients from Iran. MLPA is a reliable screening method that analyzes all 79 exons of the DMD gene and identifies deletions, duplications and NGS was the second genetic study to determine point mutation (nonsense, missense, splice site) (Sarrazin et al. 2014, Mittal et al. 1997, Hoffman et al. 1993).
Diagnosis in 85.8% of our patients confirmed by MLPA which in previous studies mentioned 63–79.5% sensitivity for this method. The reported deletion rate for MLPA-confirmed Iranian cases of DMD was 93%. Deletions were the most prevalent mutation and accounted for 79.1% of mutations, followed by nonsense mutations, duplications, splice sites representing 12.8%, 6.8%, and 1.3%, respectively. The distribution and frequency of mutations are similar to the findings from other studies in DMD patients (Zamani et al. 2015, Zamani et al. 2020). Exon 44 was the most frequently deleted single exon in the present study, reported exon in other study were exon 45 and 51. Among multiexon deletions in our study, exons 45–50 and 45–52 were the most commonly involved, which is also consistent with prior reports. The largest deletion found in our study extended from exons 3 to 44 in the proximal part. The largest deletion in previous reports was 8–47. Distribution of the patient’s mutation site on 79 exons revealed 47.4% in the distal part, 35.5% in the proximal part, distal and proximal in 1.3% cases and distal deletions constituted 57% of the deletions in the DMD which this distribution is accordant with previous reports (Vengalil et al 2017, Zamani et al. 2015, Zamani et al. 2020).
Mutations in the DMD gene can bring to a wide spectrum of clinical phenotypes which are strongly correlated to the characteristics of molecular changes and the degree of dystrophin protein deficiency originated by the mutation (Mital et al. 1998, Zamani et al 2016).The Genotype-Phenotype correlation has been characterized in our study: we assessed the possible effect of DMD genotype on disease progression. We explored the progression of the disease by NSAA score in mutations by considering genetic therapies. Comparison of NSAA scale at the beginning years of assessment, before decline in the motor function, showed a considerable finding, there was significantly different in NSAA score between deletion and nonsense groups at the age of 3 years (P = 0.036) and 3.5 years (p = 0.04) that revealed stronger motor function in nonsense mutation group before disease progression. We observed that individuals with duplication deteriorate minimally slower (1.25 unit/year) when compared with individuals with nonsense and deletions; however, this did not meet significance as Muntoni.F et al study and in contrast with Bello.L research group analysis (Muntoni et al. 2019). Moreover, no difference was observed in the age of loss of walking ability between the specified genetic groups. No correlation between genotype with motor delay and rate of LOA was seen but we found that contracture was more in nonsense mutations that were significant (P = 0.03).
Hereafter, no significant findings to correlate between mutation site and phenotype in Iranian boy was in contrast with the southern India study which revealed the earlier onset of wheelchair dependency in the distal region mutations. We provide a piece of obligatory information for future novel gene therapies in this area. Exon skipping method offers new hope for DMD patients with large deletion mutations. So far, clinical trials pointed to ‘skipping’ exon 51, exon 53, and exon 45 have been conducted in many countries (Ricotti et al. 2016).
Management strategies for standard DMD care, of which pharmacological treatment and rehabilitation are available. In the present study, we provided information concerning DMD treatment in Iran. Currently, glucocorticoids are the only drug that does improve muscle strength and function in DMD by evidence-based medicine (Manzur et al. 2008). The rate of steroid treatment has reached 41%-76% in developed countries and data showed escalated corticosteroid assumption in recent years 18. However, in Iran, the study of glucocorticoid therapy is rare. In our database based on patients, 91.9% of diagnosed DMD patients had commenced taking glucocorticoids. Deflazacort was the most type in corticosteroid therapy (83.8%). The main reasons for not using glucocorticoids were parents’ refusal or steroid side effects. The drug compliance of each patient had been ensured. Compliance with rehabilitation was seen in 54.1% of Iranian DMD boys. Also, we consider the effect of taking glucocorticoids and rehabilitation on DMD natural history. Our investigation on standard DMD care showed that most cases had positive steroid taking and rehabilitation compliance and had no significant difference in the application of standard therapies that were seen in each mutation group. Therefore we could not evaluate the confounder effect of glucocorticoids and rehabilitation on Genotype-Phenotype correlating.