The case of twin-sisters, 24 years old, showing congenital squint, that was corrected by surgery, hypermetropia and astigmatism is presented. The ophthalmoscopic examination revealed in one eye of both sisters, and specular-like, tortuosity of the retinal vessels, which in a subject is accompanied by twisted arteries in the vitreous body; in the other twin-sister an epipapillary membrane was observed, which is present in analogous form also in a single born brother. Furthermore, dystrophic lesions of the retina were present specular-like in both sisters. It is the first time that such a malformative syndrome is observed in concordant MZ twins.

The observation of twin-brothers of 4 years affected by congenital squint caused by ophthalmoplegia of Musculi recti externi, probably nuclear in origin, is described. This is the second report on concordant ophthalmoplegia in MZ twins.

In MZ-twin-sisters, aged 19 and underdeveloped from the psychophysical viewpoint, the Authors have indentified the presence of a Verhoeff's hypertropia due to occlusion, concordant and congenitally associated with squint and nystagmus. The latter is present in the mother and in a single born sister too, who is affected also by heterophoria. This is the first report on hypertropia due to occlusion in twins.

According to the results found in literature Microcephaly — better Micrencephaly — is a syndrom with a very heterogenous pathogenesis which often remains unclarified. Its etiology, though occasionally purely exogenous, seems to be mostly hereditary in the sense of monomeric recessivity, as the experiences, so far rather scanty, of research in families and in twins show.

The so-called Microcephalia vera is to be considered identical with this mono-recessive form.

Our data may be divided in four groups:

Group I comprises 35 cases of verified or almost sure M. vera in 23 sibships. The diagnosis are mainly assured by clinical data and photos and in 4 cases by post mortems, 3 of them having been most carefully examined under the guidance of brain-anatomists like C. v. Monakow, M. Minkowsky and E. Grünthal whose publications in detail are referred to here. The Sex-Ratio in our cases (17 male and 18 female) is practically 1:1, therefore deviating considerably from that found in Japan and even more from that found in England and in Holland.

The application of Weinberg's sib-Method to our thoroughly studied, non-selected series gives the percentage of 24,2 ± 6,2 largely corresponding with the theoretical expectation for the assumption of simple recessivity.

A parental consanquinity was only found in 10 families though even the IV. - V. Canonical degree was also considered twice and though about a third of our patients originate from isolates. The number of I. and II. cousin-marriages occur but three times each (together 26%). Further, 1 case of incest between father and daughter is described.

The main complications in our cases of M. vera are epileptic fits and fits of excitement with aggressive tendencies. An encephalocele was found only once and other states of dysraphy nowhere prevailed; neither did cerebral tumors, phacomatosis and other systematised nervous affections, as well as mongoloid idiocy, disturbances of metabolism and somatic malformations. Also psychoses were not above the average in the kinships concerned.

General spasticity, a symptom found regularly in their cases by other authors was only met with in a minority of our cases. Possibly there may exist heterogenity in M. vera, which phenotipically manifests itself by the presence or absence of general spasticity.

Since in Switzerland by far not all cases of M. are interned, the frequency of M. vera is difficult to ascertain. About half of our patients died in early childhood and maybe many die through abortions, the gene involved being semilethal.

Growth and life-span can rarely be normal even in high-grade microcephalic idiots. Most of them, however, are undersized, exceptionally real dwarfs.

Among the non microcephalic sibs of our patients we found a considerable number of feebleminded and bordeline cases, showing — but not always — a lessened head-circumference. In the parents of our microcephalics, however, only exceptionally an intellectual deficiency was stated, more frequently as a matter of fact a lessened head-circumference. The very heterozygotes are not at all always characterised physically and mentally or even in one respect.

Our three other groups seem to refer to a secondary microcephaly and therefore are restricted to isolated cases. In one kinship a microcephalic boy is first cousin of an idiot with hydrocephaly. In another kinship with apparently simple recessive deaf-mutism and idiocy one patient shows microcephaly. In a third family with four sibs of clincally diagnosed cases of diffuse cerebral sclerosis each affected member was also microcephalic; here we have to deal probably — as the parents are II. cousins — with a particular specific simple recessive gene.

Two errors in an earlier paper are corrected. The general conclusions arrived at originally remain unchanged.