<unk>  is often expressed in the form of moderate to severe mental retardation, hypotonia, and characteristic dysmorphia. Hyperactivity in the patient, along with severe feeding difficulties as an infant and even until teenage years are common. However, most notable are the characteristic dysmorphic facial features of patients. Patients often display narrow, elongated faces with reduced facial movements due to muscle atrophy. Characteristics can also include protruding ears, flared eyebrows, a high, narrow nasal bridge, and an open mouth appearance with a high-arched palate and dysphonic screech.
Birk-Barel syndrome
Halperin-Birk syndrome
Hurler syndrome
Hecht Scott syndrome
Kindler syndrome
Smith Martin Dodd syndrome
Baboon syndrome
Pelger–Huët anomaly