Puerto Rican Infant Hypotonia Syndrome

Clinical Features

Qazi et al. (1994) reported a seemingly distinct and 'new' syndrome in 3 unrelated Puerto Rican boys. Features were marked, central, nonprogressive hypotonia, chronic constipation, severe psychomotor retardation, seizures or abnormal electroencephalogram or both, abnormal dermatoglyphics, delayed bone age, dysharmonic skeletal maturation, and preponderance and larger size of type 2 muscle fibers. Additional findings included narrow and high-arched palate, prominent nasal root, long philtrum, distended abdomen, and drooling from open mouth. Two of the boys had undescended testes, hypertelorism, and tapered fingers. Birth weight, postnatal physical growth, and head size were average. Photographs of the 3 demonstrated the open mouth and other facial features. The 3 sets of parents were thought to be unrelated. Chronic constipation was associated with the distended abdomen in all 3 of the boys. Dysharmonic skeletal maturation was a term applied by Poznanski et al. (1971) to describe differences in the degree of ossification in the carpals, metacarpals, and phalanges. In the 3 patients, delayed bone age, as indicated by lack of ossification of the carpal bones at age 3 years despite good physical growth, was a striking finding. The paucity of type 1 muscle fibers, the predominance of type 2 fibers, and, in 2 of the patients, the greater size of type 2 fibers than type 1 fibers was referred to as congenital fiber type disproportion (CFTD). Like dysharmonic skeletal maturation, it is considered a nonspecific finding. Qazi et al. (1994) suggested that the disorder may be X-linked and that it may be an unusually frequent cause of hypotonia in infants of Puerto Rican Hispanic origin.