Delayed newborn screening

Biotinidase deficiency is an autosomal recessive disorder with an estimated incidence of 1 in 72,000-126,0(X). Many newborn-screening programs of genetic diseases include testing for this enzyme. Prompt treatment with oral biotin administration of 5-20 mg/d in affected infants will prevent clinical consequences. If the treatment is delayed, neurological manifestations (e.g., hearing loss and optic atrophy) and developmental delay occur and may not revert to normal. 

The disease develops at 3 to 6 months of age and it is characterised by developmental delay, eczema, hyperactivity and mental retardation. Newborn babies are routinely screened for PKU in many countries. Treatment is a phenylalanine-restricted diet and supplementation with tyrosine. 

Congenital hypothyroid disorders occur with a frequency of one in every 4000 live births (pp. 144—145). If diagnosed at an early age. replacement thyroid hormone can be given and normal development can occur. Delays in treatment result in cretinism (see p. 144). Elevated T.SH, measured in blood spots, is diagnostic of disorders of the thyroid itself, i.e. primary neonatal hypothyroidism. The TSH screening test does not pick up pituitary dysfunction in the newborn. 

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