Selective intestinal malabsorption of vitamin B(12) causing juvenile megaloblastic anemia (MGA; MIM# 261100) is a recessively inherited disorder that is believed to be rare except for notable clusters of cases in Finland, Norway, and the Eastern Mediterranean region. The disease can be caused by mutations in either the cubilin (CUBN; MGA1; MIM# 602997) or the amnionless (AMN; MIM# 605799) gene. To explain the peculiar geographical distribution, we hypothesized that mutations in one of the genes would mainly be responsible for the disease in Scandinavia, and mutations in the other gene in the Mediterranean region. We studied 42 sibships and found all cases in Finland to be due to CUBN (three different mutations) and all cases in Norway to be due to AMN (two different mutations), while in Turkey, Israel, and Saudi Arabia, there were two different AMN mutations and three different CUBN mutations. Haplotype evidence excluded both CUBN and AMN conclusively in five families and tentatively in three families, suggesting the presence of at least one more gene locus that can cause MGA. We conclude that the Scandinavian cases are typical examples of enrichment by founder effects, while in the Mediterranean region high degrees of consanguinity expose rare mutations in both genes. We suggest that in both regions, physician awareness of this disease causes it to be more readily diagnosed than elsewhere; thus, it may well be more common worldwide than previously thought.

Mutations in the melanocortin 4 receptor gene (MC4R) are the most common cause of monogenic human obesity. As part of our ongoing project entitled 'Turkish Obesity Genome Study' we determined the nucleotide sequence of the entire coding region of the MC4R gene in 40 morbidly obese subjects from independent families. Here we report a novel heterozygous mutation (N274S) in an adult female obese individual (age: 52 yrs, BMI 41.7 kg/m(2), height 158 cm, weight: 104 Kg). The sister of the index case (age: 55 yrs, height: 160 cm, weight: 110 Kg, BMI: 43 kg/m(2)) also carries the same mutation. Although both sisters were morbidly obese and hypertensive the index case had normal plasma insulin and fasting blood glucose levels whereas her sister had type 2 diabetes mellitus. No abnormalities of the reproductive function were present. Despite marked hyperphagia in childhood both sisters had a history of relatively diminished intensity of appetite after the age of 20. Of notice, index case was diagnosed to have cyclothymia whereas her sister was being treated for bipolar affective disorder. Detailed clinical evaluation revealed normal bone mineral density and serum calcium parameters as well as intact thyroid axis and hypothalamus-pituitary-adrenal axis in both patients. The human MC4-R deficient phenotype resembles the murine deficient state with regard to preserved reproductive function although hyperphagia, increased linear growth and absence of diabetes in mice are not observed in humans. Affected individuals have hyperphagia in childhood, which looses intensity later in life, and they also present with normal height and diabetes mellitus. Accumulating evidence indicate that melanocortin endocrine system or defective melanocortin signaling has inherently different characteristics in mice and humans resembling the variation observed with regard to leptin deficiency in both species.

We have determined the beta S haplotypes in 709 patients with sickle cell anemia, 30 with SC disease, 91 with S-beta-thalassemia, and in 322 Hb S heterozygotes from different countries. The methodology concerned the detection of mutations in the promoter sequences of the G gamma- and A gamma-globin genes through dot blot analysis of amplified DNA with 32P-labeled probes, and an analysis of isolated Hb F by reversed phase high performance liquid chromatography to detect the presence of the A gamma T chain [A gamma 75(E19)Ile----Thr] that is characteristic for haplotype 17 (Cameroon). The results support previously published data obtained with conventional methodology that indicates that the beta S gene arose separately in different locations. The present methodology has the advantage of being relatively inexpensive and fast, allowing the collection of a vast body of data in a short period of time. It also offers the opportunity of identifying unusual beta S haplotypes that may be associated with a milder expression of the disease. The numerous blood samples obtained from many SS patients living in different countries made it possible to compare their hematological data. Such information is included (as average values) for 395 SS patients with haplotype 19/19, for 2 with haplotype 17/17, for 50 with haplotype 20/20, for 2 with haplotype 3/3, and for 37 with haplotype 31/31. Some information on haplotype characteristics of normal beta A chromosomes is also presented.

A total of 25 unrelated Hb H patients were studied at the DNA level. Ten different genotypes were found to be responsible for the disease. The most prevalent alpha-thalassemia-2 determinant was the alpha alpha/-alpha (3.7) kb deletion (56%) which was followed by a nondeletional type of alpha-thalassemia, namely the pentanucleotide deletion in the 5' first intervening sequence splice junction [alpha(-5nt) alpha] (16%). The two most frequent alpha-thalassemia-1 determinants were alpha alpha/-20.5 kb and alpha alpha/-17.5 kb (MED-I) deletions. In two patients, homozygosity for the polyadenylation signal mutation [alpha (PA-2)alpha] was found to be responsible for Hb H disease. Clinical and hematological expression seems more severe in patients with the alpha (-5nt) alpha deletion at the donor site of the first intervening sequence and the alpha(PA-2) alpha mutation in trans to an alpha-thalassemia-1 determinant. Homozygosity for the alpha (PA-2)alpha mutation was also found to be associated with severe phenotype.

We describe the occurrence of a chromosome with a G----A mutation at position +22 relative to the Cap site that was found in five patients with beta-thalassemia. All patients had a common type of beta-thalassemia mutation on the second chromosome, namely the frameshift at codon 8 (-AA), the IVS-I-110 (G----A) and the IVS-II-1 (G----A) mutations. The beta genes of two patients, including the 5' and 3' untranslated regions, were completely sequenced and no other mutations, except a few polymorphic sites, were observed. Dot-blot analyses failed to demonstrate this G----A mutation at +22 in nearly 400 beta-thalassemia chromosomes and 180 normal chromosomes. Heterozygotes have the features of a high Hb A2-beta-thalassemia heterozygosity, although the hematological parameters might be less abnormal than observed in heterozygotes for the more common beta-thalassemia mutations. The possibility has been presented suggesting that this mutation might impair the binding of mRNA to ribosomes. Another mutation in this segment of DNA, i.e. a C----G mutation at position +20, is observed exclusively on a chromosome which also carries the C----G mutation at IVS-II-745. It is postulated that the +20 C----G mutation accentuates the beta-thalassemia condition caused by the IVS-II-745 mutation; the mechanism might be similar to that suggested for the G----A at +22 mutation.