We report the identification and initial characterization of paralemmin, a putative new morphoregulatory protein associated with the plasma membrane. Paralemmin is highly expressed in the brain but also less abundantly in many other tissues and cell types. cDNAs from chicken, human, and mouse predict acidic proteins of 42 kD that display a pattern of sequence cassettes with high inter-species conservation separated by poorly conserved linker sequences. Prenylation and palmitoylation of a COOH-terminal cluster of three cysteine residues confers hydrophobicity and membrane association to paralemmin. Paralemmin is also phosphorylated, and its mRNA is differentially spliced in a tissue-specific and developmentally regulated manner. Differential splicing, lipidation, and phosphorylation contribute to electrophoretic heterogeneity that results in an array of multiple bands on Western blots, most notably in brain. Paralemmin is associated with the cytoplasmic face of the plasma membranes of postsynaptic specializations, axonal and dendritic processes and perikarya, and also appears to be associated with an intracellular vesicle pool. It does not line the neuronal plasmalemma continuously but in clusters and patches. Its molecular and morphological properties are reminiscent of GAP-43, CAP-23, and MARCKS, proteins implicated in plasma membrane dynamics. Overexpression in several cell lines shows that paralemmin concentrates at sites of plasma membrane activity such as filopodia and microspikes, and induces cell expansion and process formation. The lipidation motif is essential for this morphogenic activity. We propose a function for paralemmin in the control of cell shape, e.g., through an involvement in membrane flow or in membrane–cytoskeleton interaction.

Here, we describe a novel missense mutation in the amyloid precursor protein (APP) causing a lysine-to-asparagine substitution at position 687 (APP770; herein, referred to as K16N according to amyloid-β (Aβ) numbering) resulting in an early onset dementia with an autosomal dominant inheritance pattern. The K16N mutation is located exactly at the α-secretase cleavage site and influences both APP and Aβ. First, due to the K16N mutation APP secretion is affected and a higher amount of Aβ peptides is being produced. Second, Aβ peptides carrying the K16N mutation are unique in that the peptide itself is not harmful to neuronal cells. Severe toxicity, however, is evident upon equimolar mixture of wt and mutant peptides, mimicking the heterozygous state of the subject. Furthermore, Aβ42 K16N inhibits fibril formation of Aβ42 wild-type. Even more, Aβ42 K16N peptides are protected against clearance activity by the major Aβ-degrading enzyme neprilysin. Thus the mutation characterized here harbours a combination of risk factors that synergistically may contribute to the development of early onset Alzheimer disease.

We describe two half-siblings with monocarboxylate transporter 1 (MCT1, SLC16A1) deficiency, a defect on ketone body utilization, that has only recently been identified (van Hasselt et al., N Engl J Med, 371:1900-1907, 2014) as a cause for recurrent ketoacidoses. Our index patient is a boy with non-consanguineous parents who had presented acutely with impaired consciousness and severe metabolic ketoacidosis following a 3-day history of gastroenteritis at age 5 years. A 12.5-year-old half-brother who shared the proband's mother also had a previous history of recurrent ketoacidoses. Results of mutation and enzyme activity analyses in proband samples advocated against methylacetoacetyl-coenzyme A thiolase ("beta-ketothiolase") and succinyl-coenzyme A: 3-oxoacyl coenzyme A transferase (SCOT) deficiencies. A single heterozygous c.982C>T transition in the SLC16A1 gene resulting in a stop mutation (p.Arg328Ter) was detected in both boys. It was shared by their healthy mother and by the proband's half-sister, but was absent in the proband's father. MCT1 deficiency may be more prevalent than is apparent, as clinical manifestations can occur both in individuals with bi- and monoallelic mutations. It may be an important differential diagnosis in recurrent ketoacidosis with or without hypoglycemia, particularly in the absence of any specific metabolic profiles in blood and urine. Early diagnosis may enable improved disease management. Careful identification of potential triggers of metabolic decompensations in individuals even with single heterozygous mutations in the SLC16A1 gene is indicated.

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