del(17)(q21.31q21.31)

Epidemiology and Etiology:

· 0.3-1.0% of MR population

· de novo (all described cases so far)

· NAHR likely mechanism

· Reciprocal microduplication syndrome has been described (1 patient)

Common sites:

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Gross features:

· Growth delay with low birthweight

· Severe hypotonia neonatally

· Oromotor dyspraxia

· Characteristic facies:

· Long facies

· Ptosis, hypotonic facies

· Blepharophimosis

· Pear-shaped nose with bulbous tip

· Hypoplastic alae nasi

· Long columella

· Large, low-set ears

· Broad chin

· Long fingers

· Scoliosis (hypotonia-related)

· Pes cavus (hypotonia-related)

· Hallux valgus (hypotonia-related)

· Pectus excavatum

· Strabismus

· Cataracts

· Ventriculomegaly (1 patient)

· Periventricular white matter changes (1 patient)

· Cardiac defects (1 patient)

Histologic features:

·

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

· 500-650 kb deletion at position 41.03-41.52 Mb on chr 17q21.31 (NCBI 36.1)

· NAHR most likely mechanism

· There is a common 900 kb inversion polymorphism here

· H2 haplotype (20% of Europeans and Middle Easterners) also has an inversion polymorphism and in addition has a direct low-copy repeat

· Thus suitable for NAHR events

· H2 allele has been found in at least one of the parents in all families studied

· MAPT gene is likely candidate for DD

· Microtubule-associated protein tao

· Involved in axonal microtubule stability

Other features:

· Developmental delay (mild-moderate)

· Slow feeding with poor suck

· Oromotor dyspraxia

· Amiable and friendly disposition

· Frequent laughing

· Seizures (petit mal, single clonic)

· Visual disturbances

· Strabismus

· Refractive errors

· Cataracts requiring surgery at young age (ex. 10 y)

· Resemblance of Angelman syndrome

References:

· Slavotinek, AM. Novel microdeletion syndromes detected by chromosome microarrays. Hum Genet 2008;124:1–17.

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