1. Large genotype–phenotype study in carriers of D4Z4 borderline alleles provides guidance for facioscapulohumeral muscular dystrophy diagnosis
- Author
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Gabriele Siciliano, Giovanni Antonini, Stefano C. Previtali, Silvia Tripodi, Francesco Sera, Maria Antonietta Maioli, Marina Scarlato, Giuliano Tomelleri, Fabiano Mele, Angela Berardinelli, Tiziana Mongini, Corrado Angelini, Liliana Vercelli, Luisa Villa, Elisabetta Bucci, Maria Grazia D'Angelo, Lucio Santoro, Lorenzo Maggi, Rachele Piras, Giulia Ricci, Maurizio Moggio, Roberta Telese, Antonio Di Muzio, Elena Pegoraro, Massimiliano Filosto, Monica Govi, Lucia Ruggiero, Carmelo Rodolico, Cinzia Bettio, Rossella Tupler, Ricci, G., Mele, F., Govi, M., Ruggiero, L., Sera, F., Vercelli, L., Bettio, C., Santoro, L., Mongini, T., Villa, L., Moggio, M., Filosto, M., Scarlato, M., Previtali, S. C., Tripodi, S. M., Pegoraro, E., Telese, R., Di Muzio, A., Rodolico, C., Bucci, E., Antonini, G., D'Angelo, M. G., Berardinelli, A., Maggi, L., Piras, R., Maioli, M. A., Siciliano, G., Tomelleri, G., Angelini, C., and Tupler, R.
- Subjects
musculoskeletal diseases ,0301 basic medicine ,Male ,congenital, hereditary, and neonatal diseases and abnormalities ,Weakness ,Genotype ,Facioscapulohumeral ,Science ,Genetic counseling ,030105 genetics & heredity ,Article ,03 medical and health sciences ,Medical research ,0302 clinical medicine ,medicine ,Facioscapulohumeral muscular dystrophy ,Humans ,Muscular Dystrophy ,Allele ,Myopathy ,Alleles ,Genetics ,FSHD ,Multidisciplinary ,Molecular medicine ,business.industry ,Facial weakness ,Female ,Muscular Dystrophy, Facioscapulohumeral ,Phenotype ,medicine.disease ,Penetrance ,D4Z4 borderline alleles ,Genotype-Phenotype ,Neurology ,Risk factors ,Medicine ,medicine.symptom ,business ,030217 neurology & neurosurgery ,facioscapulohumeral muscular dystrophy D4Z$ fragment borderline ,Human - Abstract
Facioscapulohumeral muscular dystrophy (FSHD) is a myopathy with prevalence of 1 in 20,000. Almost all patients affected by FSHD carry deletions of an integral number of tandem 3.3 kilobase repeats, termed D4Z4, located on chromosome 4q35. Assessment of size of D4Z4 alleles is commonly used for FSHD diagnosis. However, the extended molecular testing has expanded the spectrum of clinical phenotypes. In particular, D4Z4 alleles with 9–10 repeat have been found in healthy individuals, in subjects with FSHD or affected by other myopathies. These findings weakened the strict relationship between observed phenotypes and their underlying genotypes, complicating the interpretation of molecular findings for diagnosis and genetic counseling. In light of the wide clinical variability detected in carriers of D4Z4 alleles with 9–10 repeats, we applied a standardized methodology, the Comprehensive Clinical Evaluation Form (CCEF), to describe and characterize the phenotype of 244 individuals carrying D4Z4 alleles with 9–10 repeats (134 index cases and 110 relatives). The study shows that 54.5% of index cases display a classical FSHD phenotype with typical facial and scapular muscle weakness, whereas 20.1% present incomplete phenotype with facial weakness or scapular girdle weakness, 6.7% display minor signs such as winged scapula or hyperCKemia, without functional motor impairment, and 18.7% of index cases show more complex phenotypes with atypical clinical features. Family studies revealed that 70.9% of relatives carrying 9–10 D4Z4 reduced alleles has no motor impairment, whereas a few relatives (10.0%) display a classical FSHD phenotype. Importantly all relatives of index cases with no FSHD phenotype were healthy carriers. These data establish the low penetrance of D4Z4 alleles with 9–10 repeats. We recommend the use of CCEF for the standardized clinical assessment integrated by family studies and further molecular investigation for appropriate diagnosis and genetic counseling. Especially in presence of atypical phenotypes and/or sporadic cases with all healthy relatives is not possible to perform conclusive diagnosis of FSHD, but all these cases need further studies for a proper diagnosis, to search novel causative genetic defects or investigate environmental factors or co-morbidities that may trigger the pathogenic process. These evidences are also fundamental for the stratification of patients eligible for clinical trials. Our work reinforces the value of large genotype–phenotype studies to define criteria for clinical practice and genetic counseling in rare diseases.
- Published
- 2020