Increased serum hexosaminidase in a woman pregnant with a fetus affected by mucolipidosis II (I-cell disease)

I-cell disease (Mucolipidosis II)

I-cell disease (Mucolipidosis II) is one of the lysosomal storage diseases which presents in the neonatal period, and within six months will phenotypically resemble the severe forms of the group of disorders called the "mucopolysaccharidoses" but without mucopolysacchariduria. In Mucolipidosis II, fibrocytes exhibit "abnormal lysosomes". Activities of several lysosomal enzymes are low in fibroblast cultures but high in mucolipidosis II serum. We present a patient with I-cell disease diagnosed on the basis of clinical, radiological and biochemical features. The mother of this child was pregnant and the fetus was also found to be affected.

Prenatal diagnosis of I-cell disease in the first and second trimesters

First trimester prenatal diagnosis of I-cell disease (1 case) was based on demonstration of profound deficiency of N-acetylglucosamine 1-phosphotransferase in chorionic villi and in cultured trophoblasts derived from the chorionic villus specimen. Deficiency of this enzyme in cultured amniotic fluid cells obtained via amniocentesis was the basis for prenatal diagnosis of I-cell disease in the second trimester (2 cases). In both procedures, the diagnosis was corroborated by the finding of intracellular deficiency and extracellular elevation of multiple lysosomal enzymes in the fetal cell cultures (trophoblasts and amniotic fluid cells), as well as a significant increase in several lysosomal enzyme activities in the maternal serum.

Maternal serum hexosaminidase A in pregnancy: effects of gestational age and fetal genotype

The diagnostic usefulness of sulfated fluorogenic substrates in carrier detection of Tay-Sachs disease in serum during pregnancy was assessed by testing coded samples. Gradual increase in serum hexosaminidase activities toward these substrates was observed throughout pregnancy in both carrier and non-carriers of the Tay-Sachs gene, but absolute discrimination between the 2 genotypes could not be achieved even when values were compared within the same gestational age. Examination of isolated isozyme fractions with the sulfated substrates showed that the increased activities during pregnancy were due to a genuine increase in hexosaminidase A and not associated with the elevation of hexosaminidase I (or P), which was evident only with unsulfated substrates. The extent of the increase was influenced by the genotype of the fetus as indicated by higher values in pregnant carriers who carried non-carrier fetuses. We conclude that determination of serum hexosaminidase A during pregnancy by sulfated fluorogenic substrates may have a prenatal diagnostic value when used in obligate heterozygotes for Tay-Sachs disease, but is unreliable for screening purposes.

First trimester prenatal evaluation for I-cell disease by N-acetyl-glucosamine 1-phosphotransferase assay

First trimester prenatal diagnosis was offered to a couple at risk for having a child with I-cell disease (mucolipidosis II). The prenatal evaluation was based for the first time on examination of N-acetylglucosamine 1-phosphotransferase activity, deficiency of which is the primary biochemical defect in both I-cell disease and pseudo-Hurler polydystrophy (mucolipidosis III). Heterozygote levels of this enzyme activity were determined in chorionic villi obtained at 9 weeks of gestation, as well as in cultured trophoblasts derived from this specimen, and led to the diagnosis of an unaffected fetus. This procedure has advantages over that based on detection of abnormal intracellular-extracellular distribution of lysosomal enzyme activities, which is expressed only in homozygotes and fully expressed only in cell culture specimens.

Fetal mucolipidosis II (I-cell disease): radiologic and pathologic correlation

A pregnant woman whose previous child had a diagnosis of I-cell disease was referred for evaluation of the fetus. Fluid obtained by amniocentesis and maternal serum showed abnormally increased levels of lysosomal enzymes suggesting that the fetus had I-cell disease. Sonography at 18 weeks showed abnormally short femurs and intrauterine growth retardation. The pregnancy was electively terminated at 19 weeks' gestation and the diagnosis was confirmed. Radiographs of the fetus demonstrated that the bony dysplasia is present early in fetal life with diffuse decrease in bone mineralization, a coarse, lacy, trabecular pattern, overall shortening and under-modelling of the long bones, subperiosteal bone deficiency in the diaphysis giving the appearance of periosteal new bone, hypoplasia of the anterior superior aspect of the upper lumbar vertebral bodies, broad ribs, abnormal pelvis with squared iliac wings and flattened acetabular roofs, and a small irregular calcaneal ossification center. There was good correlation between the radiographic findings and the microscopic findings in the bones. We observed deficient endosteal bone formation, small epiphyses, and poorly developed intervertebral discs. We speculate that this indicates impaired production of extra-cellular matrix by several different types of specialized mesenchymal cells. Abnormalities of transport of glycoproteins other than lysosomal enzymes or excess of extracellular acid hydrolases may be involved in the pathogenesis.