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We present the second case of monochorionic diamniotic (MC/DA) conjoined twins. There was minimal conjunction, which was predominantly extrafetal and confined to the periumbilical ventral region. The omphalopagus twins, attached to a single forked umbilical cord, were connected by a shared umbilical hernia containing the ileum of twin B. The only visceral conjunction, located just within the belly of twin A, was midileal with the 2 separate ileums converging toward a short segment of shared muscularis propria and of side-to-side fistulization. Gastrointestinal and musculoskeletal anomalies were present in both twins with severe amyoplasia and arthrogryposis multiplex in twin A. Possible mechanisms underlying this unusual form of MZ twinning are discussed.

Kyphomelic dysplasia is a rare form of generalized skeletal dysplasia with about 15 cases described so far in the literature. We present the clinical, radiological, and pathological findings of an antenatally detected female fetus affected with this disorder. The differential diagnoses of prenatal and perinatal semilethal skeletal dysplasias and salient features of documented cases of kyphomelic dysplasia are presented.

A gene responsible for X-linked mental retardation with macrocephaly and seizures (MRX38) in a family with five affected males in three generations was localized to Xp21.1-p22.13 by linkage analysis. Recombination events placed the gene between DXS1226 distally and DXS1238 proximally, defining an interval of approximately 14 cM. A peak lod score of 2.71 was found with several loci in Xp21.1 (DXS992, DXS1236, DXS997, and DXS1036) at a recombination fraction of zero. The map intervals of 5 X-linked mental retardation loci, MRX2 (Xp22.1-p22.2), MRX19 (Xp22), MRX21 (Xp21.1-p22.3), MRX29 (Xp21.2-p22.1), and MRX32 (Xp21.2-p22.1), and two syndromal mental retardation loci, Partington syndrome (PRTS; Xp22) and Coffin-Lowry syndrome (CLS; Xp22.13-p22.2), overlap this region. As none of these display the same phenotype seen in the family reported here, this X-linked mental retardation locus may represent a new entity.

Mucolipidosis III (pseudo-Hurler polydystrophy) is an autosomal recessively inherited Hurler-like disorder without mucopolysacchariduria. Previous reports have noted a constellation of laboratory features similar to that described for mucolipidosis II (I-cell disease). Studies were carried out on a series of 15 patients. Twelve were found to have changes in serum and cultured fibroblasts which consisted of marked elevations of several acid hydrolases in serum with low levels of the same enzymes in cultured cells, a marked increase in dense cytoplasmic inclusions and abnormal radioactive sulfate kinetics. The clinical features of these 12 patients comprise a phenotypic entity. Despite clinical similarity, the 3 remaining patients were not felt to represent mucolipidosis III. The basic defect in mucolipidosis III remains unknown, but is suggested that the defect is similar to that of mucolipidosis II, from which it must be distinguished clinically.

Infantile cortical hyperostosis is a rare proliferative bone disease affecting infants under the age of 6 months. In 1961 a large family of French-Canadian origin in which 14 children in three generations were affected was described. Since then 20 new cases have been found in this family. This is the largest familial aggregation of this disease reported in the literature to date. On the basis of the findings in this pedigree, the familial form of the disease appears to be transmitted by a single autosomal dominant gene with incomplete penetrance and variable expressivity.

The triad or "prune belly" syndrome comprising deficient abdominal muscles, megaloureters with gegacystis and undescended testes has been considered a fairly rare anomaly. The Canadian Province of Saskatchewan appears to have had an unusually high incidence of this condition and it was hoped that epidemiologic investigation of the ten most recent cases might contribute information about the basic etiology of the syndrome. It is suggested that a previously unreported association with monozygotic twinning, apparent in the presently reported series, along with the well-recognized almost exclusive limitation of the syndrome to males, may provide major clues in further investigations of this condition.