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Amniotic fluid N-acetyl-beta-D-glucosaminidase (NAG) activity was measured in 21 normal pregnancies to determine reference values, and in 10 pregnancies with fetuses who had prenatally recognised renal and urinary tract malformations. The normal values obtained at 17-19 and 28-31 gestational weeks did not differ, and an activity of 105 units NAG/mmol creatinine was the upper limit of the normal range. Raised NAG activities were found in four fetuses with oligohydramnios and severe bilateral renal disease, and also in two infants with a normal amount of amniotic fluid, only unilateral renal lesions, and a normal renal function after birth. Three of four cases with normal NAG activities had malformations without kidney damage, but one baby with prune belly syndrome was subsequently found to have dysplastic kidneys and renal failure. Our preliminary results suggest that a high level of NAG activity in the amniotic fluid indicates unilateral or bilateral kidney damage but is not proof of intrauterine renal failure.

Tubular aggregates (TAs) are aggregates of densely packed tubules in human skeletal muscle fibers with particular histochemical and ultrastructural features that most probably arise from the sarcoplasmic reticulum. Some studies have shown an additional mitochondrial origin of TAs. We studied the histopathological spectrum and clinical features in a large cohort of patients with TAs in their muscle biopsy (106 biopsies), derived from our muscle biopsy archive (15,412 biopsies in total). In particular, we examined light microscopic, enzyme histochemical, immunohistochemical and ultrastructural features in the muscle biopsies, as well as the patients’ clinical data. We found TAs in 0.5% of all muscle biopsies. Based on the size of TAs, we identified two sub-groups: (1) myopathies with large TAs (29 biopsies) in type 2 fibers and sometimes also in type 1 fibers, absence of any other associated disorder, and a familial history in half of the cases, and (2) myopathies with small TAs (77 biopsies), exclusively in type 2 fibers, presence of another associated disease in the majority of patients and mostly no familial history. In the sub-group with large TAs, we observed a high variability of ultrastructural changes. The most frequent clinical symptom in both groups was limb muscle weakness. No significant differences in clinical presentation, age at onset or disease duration at the time of biopsy were found between the two groups. In conclusion, myopathies with TAs can be sub-divided into a group with large TAs, probably corresponding to the so-called primary TA myopathies, and into a group with small TAs as a feature of another underlying condition.