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In this study we report the results of a systematic etiological, clinical genetic study in 307 institutionalized mentally retarded adult males. Special attention is paid to the nosology of X-linked mental retardation. During the survey 63 males with one or more 'Martin Bell'-like features were identified in whom repetitive fragile Xq27-3 screenings were negative. In 13 of them, belonging to 9 different families, pedigree data were compatible with X-linked inheritance. This finding confirms the existence of one (or more) forms of fra(x) negative mental retardation with 'Martin Bell'-like features.

Two unrelated patients with Coffin-Lowry syndrome are described. The main characteristics of a typical face, thick hands with tapering fingers and a transverse hypothenar crease, general hypotonia with extensible joints made diagnosis possible before the age of 6 months. A persistent large anterior fontanel beyond the age of two years may be another associated finding. Retarded bone age, coarsity of the face and skeletal malformations considered characteristic in adult patients were not present. Early recognition of Coffin-Lowry syndrome is important for genetic counseling and prevention of severe skeletal malformations.

During a systematic survey of the mentally retarded, 3 related females were seen with a similar syndrome of shortness, unusual combination of craniofacial anomalies (trigonocephaly; bulging forehead; flat face; posteriorly angulated, lowset ears and microretrognathia), and genital hypoplasia in all 3 cases, and multiple pterygia in one. The facial changes were also noted in 2 grandmothers and may indicate autosomal dominant inheritance of this presently "private" MCA/MR syndrome.

In this report we describe two fra(X) adults and two prepubertal fra(X) brothers with a combination of distinct phenotypic findings: extreme obesity, short stature, stubby hands and feet and diffuse hyper-pigmentation. These clinical abnormalities may be an additional indication of a specific hypothalamic disturbance in the fra(X) syndrome.

The familial occurrence of the Coffin-Siris syndrome, combining a typical facial appearance with hypoplastic or absent fifth finger- or toenails, is reported. The full expression of the syndrome was present in two sisters, and partial clinical manifestations were present in their mentally borderline father. The relevant literature is reviewed, and the relation and confusion with other mental retardation syndromes, mainly the Coffin-Lowry syndrome, is discussed.

Mental retardation associated with short stature, craniofacial dysmorphism, macrodontia and minor skeletal anomalies is reported in two sisters and their mother. The similarity with and the relationship to the KBG syndrome is discussed and the importance of clinical syndrome identification in familial mental retardation is emphasised.

Severe limb anomalies with radial aplasia and hypodactylia are reported in a male newborn with 4p deletion syndrome. In apparent contradiction with previous reports, this finding indicates that the radial aplasia, as frequently observed in patients with ring chromosome 4, seems to be more likely related to the 4p deletion, rather than to the 4q deletion.

We describe here a female infant, exhibiting lethal short-limbed dwarfism. The condition superficially resembled achondrogenesis. However, unlike achondrogenesis there was an associated severe spondylocostal dysostosis and major non-skeletal anomalies, particularly a cerebellar Dandy-Walker cyst, cardiovascular and urogenital malformations. The chondroosseous morphology was nonspecific. The case is believed to be unique. It is therefore suggested that this constellation of anomalies constitutes a "new" lethal syndrome, different from the delineated chondrodysplasias.