Behind this still little-known name lies a rare syndrome that disrupts development and communication. Autism spectrum disorders are described in more than half of cases. Diagnosis sometimes does not occur until adulthood.
Phelan-McDermid syndrome is a rare, largely unknown genetic disorder. The sister of actress Joséphine Japy has it. She is dedicating a film to her, “Who Shines in Combat”, expected in theaters on December 31, 2025. “My sister was 25 years old (when the diagnosis came, Editor’s note). (…) 25 years of uncertainty where my mother was not listened to in her feelings, in her intuition that something was wrong from the first years of my sister’s life” the actress shared with Laurent Delahousse, on December 7 on France 2.
International estimates speak of approximately 1 in 30,000 births. Today, a little more than 1,200 cases are officially listed in global registers, but specialists point out that this figure is probably far below reality: many children with developmental delays do not yet benefit from sufficiently in-depth genetic sequencing to precisely identify the origin of their difficulties.
Phelan-McDermid syndrome is linked to an anomaly located at the end of chromosome 22, notably affecting the SHANK3 gene, essential for the proper functioning of connections between neurons. In the majority of cases, this genetic anomaly occurs spontaneously, without a family history. This explains why the diagnosis is only made after several months of questions surrounding the child’s development.
A “soft” baby who cannot hold his head
The clinical picture is very variable, but certain signs are characteristic. From the first months, parents often report hypotonia, a “soft” baby who has difficulty holding his head. An overall developmental delay is almost constant, particularly in the area of language, which is particularly affected: late speech, very limited vocabulary or, in certain cases, absence of oral language. Autism spectrum disorders are common, described in more than half of cases according to Orphanet: difficulties with social interactions, repetitive behaviors, hypersensitivity or hyposensitivity to noise, touch or certain textures. Other symptoms may be associated with it: sleep disorders, eating difficulties, motor delay, digestive disorders or even epilepsy in a significant proportion of children. This great heterogeneity explains why there is no “typical profile” of the syndrome. Two affected children can present very different manifestations, which complicates the diagnostic process.
The available data, from expert centers and the French PNDS, are reassuring: life expectancy is generally normal. The syndrome itself is not considered a life-threatening condition. On the other hand, certain complications – epilepsy, heart or kidney problems, breathing or eating difficulties – require regular monitoring. As with other neurodevelopmental disorders, early treatment (speech therapy, psychomotor skills, occupational therapy, support for sensory and sleep disorders) significantly improves the quality of life and the level of autonomy in adulthood. Family associations also play an essential role in supporting parents and raising awareness of this disease, which is still too little identified.
