Monosomy 18q syndrome

Monosomy 18q syndrome, also known as 18q deletion syndrome or distal 18q deletion syndrome (del(18q)), is a rare chromosomal disorder caused by partial deletion of the long arm (q arm) of chromosome 18. The size and location of the deleted segment vary among affected individuals, which contributes to a wide spectrum of clinical severity. This condition affects multiple body systems and is typically identified at birth or during early childhood. Key clinical features include intellectual disability of variable degree, short stature, hypotonia (reduced muscle tone), hearing impairment (often sensorineural), and characteristic facial features such as a flat midface, deep-set eyes, a carp-shaped mouth, and prominent antihelix of the ears. Many individuals have limb anomalies including tapering fingers and abnormal toe placement. Congenital heart defects, cleft palate, genital abnormalities (particularly in males, such as micropenis or cryptorchidism), and white matter abnormalities on brain MRI (dysmyelination) are also frequently observed. Endocrine issues, including growth hormone deficiency and thyroid dysfunction, may occur. Seizures are reported in some patients. There is no cure for monosomy 18q syndrome, and management is supportive and symptom-directed. Treatment may include growth hormone therapy for short stature, hearing aids or cochlear implants for hearing loss, cardiac surgery for congenital heart defects, speech and occupational therapy, and special educational support. Thyroid hormone replacement may be needed if hypothyroidism is present. Regular developmental assessments and multidisciplinary follow-up are essential to optimize outcomes. The Chromosome 18 Registry and Research Society provides resources and supports ongoing research into genotype-phenotype correlations to improve individualized care.

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