Congenital disorders of glycosylation or Carbohydrate-Deficient Glycoprotein Syndrome
Congenital disorders of glycosylation or carbohydrate-deficient glycoprotein syndrome presents in the neonatal period with inverted nipples, hypotonia, abnormal distribution of fat (Figure 123.1 A-C) and pontocerebellar hypoplasia. Trunk hypotonia may be more pronounced than limb hypotonia. The abnormal accumulation of fat produces a puffy and uneven skin (Figure 123.1 B), and increased subcutaneous tissue around the external genitalia and around the buttocks (Figure 123.1 C). The combination of slender legs (limb waisting due to hypoactivity) and prominent deposition of fat in the buttocks produces a characteristic appearance (Figure 123.1 C). The diagnosis of carbohydrate-deficient glycoprotein syndrome is established by the detection in serum or CSF of abnormal transferrin isoforms. The tests for this purpose are: (1) carbohydrate-deficient transferin assay, or (2) isoelectric focusing of serum transferrin. The disease is due to hypoglycosylation of glycoproteins. There are several types of congenital disorders of glycosylation. Type I is due to a deficiency of phosphomannomutase. Congenital disorder of glycosylation type I is an autosomic recessive disease. The abnormalities is probably in chromosomes 16p. The dysfunctional cellular organelle is probably the endoplasmatic reticulum.

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Figure 123.1— Congenital disorders of glycosylation or carbohydrate-deficient glycoprotein syndrome. [A] accumulation of fat between the ear cartilage and skin; [B] puffy and uneven skin of the arm and inverted nipple; [C] prominent deposition of fat in the buttocks and waisted legs.

Congenital Pontocerebellar Hypoplasia
Neonates with congenital pontocerebellar hypoplasia may be hypotonic at birth. Congenital pontocerebellar hypoplasia may have an autosomal dominant or recessive inheritance. Magnetic resonance imaging of the brain is diagnostic (Figure 123.2). Pontocerebellar hypoplasia may occur in association with spinal muscular atrophy.

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Figure 123.2—Congenital pontocerebellar hypoplasia. [A] T1-weighted sagittal image demonstrates brainstem atrophy and cerebellar hypoplasia. [B] T1-weighted axial image demonstrates an empty posterior fossa.