Phenotypes of galactosaemia in infants screened at birth.

Any one of several phenotypes of galactosaemia are likely to be found in the infant with an abnormal screening test result at birth. Ascertained by analysing several kinds of biochemical data, phenotyping is an important corollary to the screening programme, as the genetic form ofgalactosaemia may determine the prognosis, course of treatment, and need for genetic counselling. We assigned the biochemical phenotypes of galactosaemia in infants with apparent deficiencies of galactose-l-phosphate uridyl transferase, detected in a newborn screening programme (Kelly et al, 1970), by applying the criteria listed in Table I and, in some instances, by including data from serial assays of the transferase and family studies.