A. Consistent (100%)
Developmental delay, functionally severe Movement or balance disorder, usually ataxia of gait and/or tremulous movement of limbs. Movement disorder can be mild. May not appear as frank ataxia but can be forward lurching, unsteadiness, clumsiness or quick, jerky motions Behavioral uniqueness: any combination of frequent laughter/smiling; apparent happy demeanor; easily excitable personality, often with uplifted hand-flapping or waving movements; hypermotoric behavior Speech impairment, none or minimal use of words; receptive and nonverbal communication skills higher than verbal ones
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B. Frequent (more than 80%)
Delayed, disproportionate growth in head circumference, usually resulting in microcephaly (≤2 SD of normal OFC) by age 2 years. Microcephaly is more pronounced in those with 15q11.2-q13 deletions Seizures, onset usually <3 years of age. Seizure severity usually decreases with age, but the seizure disorder lasts throughout adulthood Abnormal EEG, with a characteristic pattern, as mentioned in the text. The EEG abnormalities can occur in the first 2 years of life, can precede clinical features and are often not correlated to clinical seizure events
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C. Associated (20–80%)
Flat occiput Occipital groove Protruding tongue Tongue thrusting, suck/swallowing disorders Feeding problems and/or truncal hypotonia during infancy Prognathia Wide mouth, wide-spaced teeth Frequent drooling Excessive chewing/mouthing behaviors Strabismus Hypopigmented skin, light hair and eye color (compared to family), seen only in deletion cases Hyperactive lower extremity, deep tendon reflexes Uplifted, flexed arm position, especially during ambulation Wide-based gait with pronated or valgus-positioned ankles Increased sensitivity to heat Abnormal sleep-wake cycles and diminished need for sleep Attraction to/fascination with water, fascination with crinkly items such as certain papers and plastics Abnormal food-related behaviors Obesity (in the older child) Scoliosis Constipation
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