What is the cause of cat scream syndrome?

Feline scream syndrome (synonyms: feline cry disease, Lejeune syndrome named after the French scientist who described it in 1963).
The cause of the disease is a karyotype: 44 + XX, 44 + XU + deletion of part 5 of the chromosome. The diagnosis is confirmed by a karyological study using one of the chromosome identification methods.
Chromosomal feline scream syndrome is explained by partial monosomy; it develops with a deletion (with loss from a third to half, less often complete loss) of the short arm of the fifth chromosome. For the development of the clinical picture of the syndrome, it is not the size of the lost site that matters, but the specific minor fragment of the chromosome. Mosaicism by deletion or the formation of a ring chromosome is rarely observed
With this syndrome, there is:
• general developmental delay,
• low birth weight and muscle hypotension,
• moon-shaped face with wide-set eyes
a characteristic cry of a child, reminiscent of cat meow, the cause of which is a change in the larynx (narrowing, softness of the cartilage, reduction of the epiglottis, unusual folding of the mucous membrane) or underdevelopment of the larynx. The sign disappears at the end of the first year of life.