Variability in Phelan-McDermid Syndrome in a Cohort of 210 Individuals

Julián Nevado, Sixto García-Miñaúr, María Palomares-Bralo, Elena Vallespín, Encarna Guillén-Navarro, Jordi Rosell, Cristina Bel-Fenellós, María Ángeles Mori, Montserrat Milá, Miguel del Campo, Pilar Barrúz, Fernando Santos-Simarro, Gabriela Obregón, Carmen Orellana, Harry Pachajoa, Jair Antonio Tenorio, Enrique Galán, Juan C. Cigudosa, Angélica Moresco, César Saleme, Silvia Castillo, Elisabeth Gabau, Luis Pérez-Jurado, Ana Barcia, Maria Soledad Martín, Elena Mansilla, Isabel Vallcorba, Pedro García-Murillo, Franco Cammarata-Scalisi, Natálya Gonçalves Pereira, Raquel Blanco-Lago, Mercedes Serrano, Juan Dario Ortigoza-Escobar, Blanca Gener, Verónica Adriana Seidel, Pilar Tirado, Pablo Lapunzina, Spanish PMS Working Group, Mena Rocío, Lleguer Roser, Fernández-Montaño Victoria, Martín Rubén, Fernández Blanca, García-Santiago Fé, Gómez del Pozo Victoria, Peña Carolina, Alhambra Norma, García Carlos, Rodríguez Juan Ramón, Martínez-Bermejo Antonio, Málaga Ignacio, Martínez-Monseny Antonio Federico, Armstrong Judith, Anticona Jennifer, Hernando-Davalillo Cristina, San Martí Adrián Alcalá, Martorell Loreto, Yubero Delia, Nunes Tania, Callaghan Mar O´, Alonso Xenia, Ramos Federico, López Jesús Casas, López-González Vanesa, M Juliana Ballesta, Armengol Lluís, González-Meneses Antonio, Borrego Salud, Roselló Mónica, Suela Javier, Pérez-Granero Ángeles, Rodríguez-Revenga Laia

Phelan-McDermid syndrome (PMS, OMIM# 606232) results from either different rearrangements at the distal region of the long arm of chromosome 22 (22q13.3) or pathogenic sequence variants in the SHANK3 gene. SHANK3 codes for a structural protein that plays a central role in the formation of the postsynaptic terminals and the maintenance of synaptic structures. Clinically, patients with PMS often present with global developmental delay, absent or severely delayed speech, neonatal hypotonia, minor dysmorphic features, and autism spectrum disorders (ASD), among other findings. Here, we describe a cohort of 210 patients with genetically confirmed PMS. We observed multiple variant types, including a significant number of small deletions (<0.5 Mb, 64/189) and SHANK3 sequence variants (21 cases). We also detected multiple types of rearrangements among microdeletion cases, including a significant number with post-zygotic mosaicism (9.0%, 17/189), ring chromosome 22 (10.6%, 20/189), unbalanced translocations (de novo or inherited, 6.4%), and additional rearrangements at 22q13 (6.3%, 12/189) as well as other copy number variations in other chromosomes, unrelated to 22q deletions (14.8%, 28/189). We compared the clinical and genetic characteristics among patients with different sizes of deletions and with SHANK3 variants. Our findings suggest that SHANK3 plays an important role in this syndrome but is probably not uniquely responsible for all the spectrum features in PMS. We emphasize that only an adequate combination of different molecular and cytogenetic approaches allows an accurate genetic diagnosis in PMS patients. Thus, a diagnostic algorithm is proposed.