One of the principal peptide components of the amyloid plaque deposits of Alzheimer's disease in humans is the 40‐amino‐acid peptide β‐amyloid A4‐(1–40)‐peptide. The full‐length A4‐(1–40)‐peptide was chemically synthesized and the solution structure determined by two‐dimensional nuclear magnetic resonance spectroscopy and restrained molecular‐dynamics calculations. Synthetic human A4‐(1–40)‐peptide was soluble and non‐aggregating for several days in 40% (by vol.) trifluoroethanol/water. All spin systems could be unambiguously assigned, and a total of 203 sequential and medium‐range cross‐peaks were found in the NOESY (nuclear Overhauser enhancement spectroscopy) spectrum. Long‐range NOE cross‐peaks that would indicate tertiary structure of the peptide were absent. The main secondary‐structure elements found by chemical‐shift analysis, sequential and medium‐range NOESY data, and NOE‐based restrained molecular‐dynamics calculations were two helices, Gln15–Asp23 and IIe31–Met35, whereas the rest of the peptide was in random‐coil conformation. A similar secondary structure is suggested for the aggregation part of prions, the postulated causative agents of the transmissible spongiform encephalopathy. The sequence of the helical part of prion proteins was observed to be remarkably similar to the sequence of the helical part of human A4‐(1–40)‐peptide.

Neurodevelopmental disorders comprise a large and heterogeneous group of diseases, most of which are characterized by intellectual disability (ID). Although socioeconomic aspects, infectious sources, and toxic agents contribute to the prevalence of ID, genetic factors are assumed to be causative in most cases.¹ In nonconsanguineous populations, frequent causes of severe sporadic ID are de novo chromosomal aberrations or point mutations^2-4; however, in affected children from consanguineous families, autosomal recessive inheritance is assumed to be the most common cause.^5,6