Partial duplication of the short arm of chromosome X syndrome

Partial duplication of the short arm of chromosome X syndrome (also referred to as partial Xp duplication or Xp trisomy) is a rare chromosomal disorder caused by the presence of extra genetic material from the short arm (p arm) of the X chromosome. The clinical presentation varies considerably depending on the size and exact location of the duplicated segment, as well as the sex of the affected individual. In males (46,XY with a duplicated Xp segment), the condition tends to be more severe because there is no second normal X chromosome to compensate, whereas females may have a milder phenotype due to X-inactivation, though skewed inactivation patterns can influence severity. Key clinical features may include intellectual disability of variable degree, developmental delay, craniofacial dysmorphism (such as a broad nasal bridge, hypertelorism, and abnormal ear morphology), hypotonia, and growth abnormalities. In males, duplications involving the Xp21 region that includes the DAX1 (NR0B1) gene can lead to dosage-sensitive sex reversal, resulting in ambiguous or female external genitalia despite a 46,XY karyotype. Congenital anomalies affecting the heart, kidneys, and skeletal system have also been reported in some cases. Neurological involvement, including seizures and behavioral difficulties, may occur. There is no specific curative treatment for this chromosomal condition. Management is supportive and multidisciplinary, tailored to the individual's clinical manifestations. This may include early intervention programs, speech and occupational therapy, endocrine management for disorders of sex development, cardiac or renal surveillance as needed, and antiepileptic medications if seizures are present. Genetic counseling is recommended for affected families to assess recurrence risk, particularly when a parent carries a balanced chromosomal rearrangement that predisposes to the duplication.

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