Estimation of Growth Norms from Incomplete Longitudinal Data

Longitudinal studies are rarely complete due to attrition, mistimed visits and observations missing at random. When the data are missing at random it is possible to estimate the primary location parameters of interest by constructing a modification of Zellner's (1962) seemingly unrelated regression estimator. Such a procedure is developed in this paper and is applied to a longitudinal study of coronary risk factors in children. The method consists of two stages in which the covariance matrix is estimated at the first stage. Using the estimated covariance matrix a generalized least squares estimator of the regression parameter vector is then determined at the second stage. Limitations of the procedure are also discussed.     

The anti-sickling drug lawsone (2-OH-1,4-naphthoquinone) protects sickled cells against membrane damage

The ability of an anti-sickling drug lawsone, 2-OH-1,4-naphthoquinone, and two related compounds to inhibit the haematoporphyrin-sensitised photohaemolysis of normal and sickle cell erythrocytes has been investigated. The compounds appear to protect the erythrocyte membranes by reaction with transient oxidative species. Differential effects between normal and sickle cells are shown and these are attributed to the different membrane composition of irreversibly sickled erythrocytes. This report describes a possible basis for the decreased formation of irreversibly sickled cells in the presence of lawsone.     

On the distribution of aldolase isoenzymes in subcellular fractions from rat brain

As an extension of previous studies on the adsorption of aldolase (EC 4.1.2.13) in nervous tissue, the main features of the subcellular localization of this enzyme in rat brain have been investigated. The major portion of the aldolase activity in homogenates of this tissue was demonstrated to be present in association with the particulate material, and a differential distribution of the AC isoenzymes was evident between the membranes and the cytosol. Some of the enzyme which was associated with the particulate fraction was shown to be occluded rather than absorbed to the membranes. This type of association was evident in the nuclear and mitochondrial fractions, in particular, with the occluded enzyme presenting an isoenzyme content high in C-type activity, and similar to that of the cytosol. The microsomal fraction contained a high proportion of enzyme in the bound form. Isoenzyme analysis of the enzyme in this microsomal fraction revealed a preferential association between the particulate material and A-type aldolase activity. A purified membrane fraction was prepared from the primary microsomal fraction, and identified as the main site of aldolase binding. The significance of the differential binding of aldolase isoenzymes and its localization amongst the subcellular fractions of rat brain have been discussed in relation to the structural and metabolic features of this tissue, and the coupling of energy producing sequences with energy requiring processes.     

Spina bifida and anencephaly: miscarriage as possible cause.

In two retrospective Liverpool surveys the domestic, family, dietary, and medical environments of the mothers of children affected by anencephaly or spina bifida, or both (ASB) were examined. None seemed to be of more than minor importance and the findings of others were therefore examined to see if they suggested a major factor. The most promising lead came from the hypothesis that ASB is usually due to an interaction between twin fetuses or between a fetus and residual trophoblastic material from the previous normal pregnancy, particularly when this is of the opposite sex to the propositus. The sex finding was not confirmed. It was noted that hydatidiform moles, like children with ASB, were usually female and that moles and choriocarcinomas on the one hand and children with ASB on the other occurred in mothers of similar ages, but were to some extent reciprocal in geographical incidence. This suggested that trophoblastic disease might be a factor common to all three and if so then one would expect the frequency of miscarriages to be higher immediately before than immediately after the birth of an ASB child, since mole and choriocarcinoma seldom follow a normal pregnancy. An analysis of published data confirmed that this was almost certainly so. Hence residual pathological trophoblastic material from either a previous miscarriage or a co-twin may interact unfavourably with another fetus to produce ASB and this may be the primary cause of the condition. The hypothesis is consistent with the observed lack of concordance in twins, the high incidence in females, the maternal age effect, and the greater prevalence in social classes IV and V.