1p36 deletion syndrome, or monosomy 1p36, is a chromosomal abnormality characterized most commonly by a deletion in the distal segment of the short arm of chromosome one ¹.

Epidemiology

The 1p36 deletion syndrome is present in approximately 1 in 5,000 live births. It is the most common terminal deletion syndrome ². 

Clinical features

There is a broad spectrum of variability in the clinical presentation of monosomy 1p36. Some of the neurodevelopmental and physical abnormalities that may be present in 1p36 deletion syndrome are featured below ^1,3:

• growth restriction (ante- and postnatal), however, obesity can also be present in subtypes that feature hyperphagia (similar to Prader-Willi syndrome)

• dysmorphic features

  • large (and late closure) anterior fontanelle

  • brachycephaly and microcephaly

  • straight eyebrows

  • flat nasal bridge

  • midface hypoplasia

  • deep-set eyes

  • prominent forehead and chin

  • epicanthic folds

  • low set ears

• neurological abnormalities

  • developmental delay and intellectual disability 

  • seizures

  • hypotonia

  • poor suck/swallow in infancy

  • structural brain abnormalities

    • enlarged ventricles

    • cortical atrophy

    • enlarged subarachnoid space

• cardiac malformations and disorders

  • atrial and ventricular septal defects

  • patent ductus arteriosus

  • valvular disorders

  • tetralogy of Fallot

  • coarctation of the aorta

  • dilated cardiomyopathy

Radiographic features

Ultrasound

Findings on antenatal ultrasound, such as ventriculomegaly, cardiac malformations, and midface hypoplasia, sometimes associated with intrauterine growth restriction (IUGR), as well as various other anomalies, should prompt suspicion for 1p36 deletion syndrome ⁵.