We have typed 275 men from five populations in Algeria, Tunisia, and Egypt with a set of 119 binary markers and 15 microsatellites from the Y chromosome, and we have analyzed the results together with published data from Moroccan populations. North African Y-chromosomal diversity is geographically structured and fits the pattern expected under an isolation-by-distance model. Autocorrelation analyses reveal an east-west cline of genetic variation that extends into the Middle East and is compatible with a hypothesis of demic expansion. This expansion must have involved relatively small numbers of Y chromosomes to account for the reduction in gene diversity towards the West that accompanied the frequency increase of Y haplogroup E3b2, but gene flow must have been maintained to explain the observed pattern of isolation-by-distance. Since the estimates of the times to the most recent common ancestor (TMRCAs) of the most common haplogroups are quite recent, we suggest that the North African pattern of Y-chromosomal variation is largely of Neolithic origin. Thus, we propose that the Neolithic transition in this part of the world was accompanied by demic diffusion of Afro-Asiatic-speaking pastoralists from the Middle East.

Ullrich congenital muscular dystrophy (UCMD) is an autosomal recessive disorder characterized by generalized muscular weakness, contractures of multiple joints, and distal hyperextensibility. Homozygous and compound heterozygous mutations of COL6A2 on chromosome 21q22 have recently been shown to cause UCMD. We performed a genomewide screening with microsatellite markers in a consanguineous family with three sibs affected with UCMD. Linkage of the disease to chromosome 2q37 was found in this family and in two others. We analyzed COL6A3, which encodes the alpha3 chain of collagen VI, and identified one homozygous mutation per family. In family I, the three sibs carried an A-->G transition in the splice-donor site of intron 29 (6930+5A-->G), leading to the skipping of exon 29, a partial reduction of collagen VI in muscle biopsy, and an intermediate phenotype. In family II, the patient had an unusual mild phenotype, despite a nonsense mutation, R465X, in exon 5. Analysis of the patient's COL6A3 transcripts showed the presence of various mRNA species-one of which lacked several exons, including the exon containing the nonsense mutation. The deleted splice variant encodes collagen molecules that have a shorter N-terminal domain but that may assemble with other chains and retain a functional role. This could explain the mild phenotype of the patient who was still ambulant at age 18 years and who showed an unusual combination of hyperlaxity and finger contractures. In family III, the patient had a nonsense mutation, R2342X, causing absence of collagen VI in muscle and fibroblasts, and a severe phenotype, as has been described in patients with UCMD. Mutations in COL6A3 are described in UCMD for the first time and illustrate the wide spectrum of phenotypes which can be caused by collagen VI deficiency.

Homozygous or compound heterozygous IL36RN gene mutations underlie the pathogenesis of psoriasis-related pustular eruptions including generalized pustular psoriasis, palmoplantar pustular psoriasis, acrodermatitis continua of Hallopeau, and acute generalized exanthematous pustular eruption. We identified two unreported IL36RN homozygous mutations (c.41C>A/p.Ser14X and c.420_426del/p.Gly141MetfsX29) in patients with familial generalized pustular psoriasis. We analyzed the impact of a spectrum of IL36RN mutations on IL-36 receptor antagonist protein by using site-directed mutagenesis and expression in HEK293T cells. This enabled us to differentiate null mutations with complete absence of IL-36 receptor antagonist (the two previously unreported mutations, c.80T>C/p.Leu27Pro, c.28C>T/p.Arg10X, c.280G>T/p.Glu94X, c.368C>G/p.Thr123Arg, c.368C>T/p.Thr123Met, and c.227C>T/p.Pro76Leu) from mutations with decreased (c.95A>G/p.His32Arg, c.142C>T/p.Arg48Trp, and c.308C>T/p.Ser113Leu) or unchanged (c.304C>T/p.Arg102Trp and c.104A>G/p.Lys35Arg) protein expression. Functional assays measuring the impact of mutations on the capacity to repress IL-36-dependent activation of the NF-κB pathway showed complete functional impairment for null mutations, whereas partial or no impairment was observed for other mutations considered as hypomorphic. Finally, null mutations were associated with severe clinical phenotypes (generalized pustular psoriasis, acute generalized exanthematous pustular eruption), whereas hypomorphic mutations were identified in both localized (palmoplantar pustular psoriasis, acrodermatitis continua of Hallopeau) and generalized variants. These results provide a preliminary basis for genotype-phenotype correlation in patients with deficiency of the IL-36Ra (DITRA), and suggest the involvement of other factors in the modulation of clinical expression.