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1p36 Microdeletion Syndrome

Clinical Features

1p36 Microdeletion Syndrome is the most common terminal microdeletion syndrome. Prevalence in children with combined developmental delay is between 0.5 and 1.2 percent.

Notable features are often a large anterior fontanel (77%), as well as abnormalities of the central nervous system, microcephaly and hypotonia. Only a quarter of affected persons learn how to walk; mental retardation is often considerable. Approximately 60% of patients develop epilepsy with overlapping phenotypes within the first year of life (most often between 1 and 3 months of age); 60% of these cases can be well-managed without medication.

• Developmental symptoms:
  • Below average growth, often already intrauterine, rarely in the normal or above average percentile
  • Small hands and feet
  • Combined developmental delay
  • Hypotonia (95%)
• Dysmorphological symptoms:
  • low, asymmetrical ears, rotated backward (40%)
  • a flat, broadnasal bridge
  • straight eyebrows
  • pointed chin
  • Microcephaly (95%) and Brachycephaly
• Additional clinical symptoms:
  • in approx. 60% of cases: epilepsy, often beginning tonic/clonic with overlapping phenotypes
  • congenital heart defects (70%; in 23% non-compaction cardiomyopathy)
  • facial clefting (palate, lip, and jaw)
  • ametropia (65%)
  • genital dysplasia
  • kidney malformation
  • anomalies of the central nervous system

Genetic Information

1p36 Microdeletion Syndrome is caused by a microdeletion at the terminal end of the short arm of chromosome 1. The size of the deletion varies between 1.5 Mb and 10 Mb. 40% of all break points are located about 3 to 5 mb from the telomere. 70% are terminal deletions; approximately 7% of the deletions are interstitial. Break points are often located in bands 1p36.12 and 1p36.33.

The majority of cases of microdeletion 1p36 can be detected using a FISH probe specifically targeting the subtelomeric region of the short arm of chromosome 1; interstitial deletions are captured by Array-CGH analysis.

Prevalence

1 : 5 000

Diagnostic