Galactokinase deficiency is an inborn error in the first step of galactose metabolism. Its major clinical manifestation is the development of cataracts in the first weeks of life. It has also been suggested that carriers of the deficiency are predisposed to presenile cataracts developing at age 20-50 years. Newborn screening data suggest that the gene frequency is very low worldwide but is higher among the Roma in Europe. Since the cloning of the galactokinase gene (GK1) in 1995, only two disease-causing mutations, both confined to single families, have been identified. Here we present the results of a study of six affected Romani families from Bulgaria, where index patients with galactokinase deficiency have been detected by the mass screening. Genetic linkage mapping placed the disease locus on 17q, and haplotype analysis revealed a small conserved region of homozygosity. Using radiation hybrid mapping, we have shown that GK1 is located in this region. The founder Romani mutation identified in this study is a single nucleotide substitution in GK1 resulting in the replacement of the conserved proline residue at amino acid position 28 with threonine (P28T). The P28T carrier rate in this endogamous population is approximately 5%, suggesting that the mutation may be an important cause of early childhood blindness in countries with a sizeable Roma minority.

Hereditary motor and sensory neuropathy type Lom, initially identi®ed in Roma (Gypsy) families from Bulgaria, has been mapped to 8q24. Further re®ned mapping of the region has been undertaken on DNA from patients diagnosed across Europe. The re®ned map consists of 25 microsatellite markers over approximately 3 cM. In this collaborative study we have identi®ed a number of historical recombinations resulting from the spread of the hereditary motor and sensory neuropathy type Lom gene through Europe with the migration and isolation of Gypsy groups. Recombination mapping and the minimal region of homozygosity reduced the original 3 cM hereditary motor and sensory neuropathy type Lom region to a critical interval of about 200 kb. q

Investigation of 31 of Roma patients with congenital lactic acidosis (CLA) from Bulgaria identified homozygosity for the R446* mutation in the PDHX gene as the most common cause of the disorder in this ethnic group. It accounted for around 60% of patients in the study and over 25% of all CLA cases referred to the National Genetic Laboratory in Bulgaria. The detection of a homozygous patient from Hungary and carriers among population controls from Romania and Slovakia suggests a wide spread of the mutation in the European Roma population. The clinical phenotype of the twenty R446* homozygotes was relatively homogeneous, with lactic acidosis crisis in the first days or months of life as the most common initial presentation (15/20 patients) and delayed psychomotor development and/or seizures in infancy as the leading manifestations in a smaller group (5/20 patients). The subsequent clinical picture was dominated by impaired physical growth and a very consistent pattern of static cerebral palsy-like encephalopathy with spasticity and severe to profound mental retardation seen in over 80% of cases. Most patients had a positive family history. We propose testing for the R446* mutation in PDHX as a rapid first screening in Roma infants with metabolic acidosis. It will facilitate and accelerate diagnosis in a large proportion of cases, allow early rehabilitation to alleviate the chronic clinical course, and prevent further affected births in high-risk families.

A 2 bp deletion in exon 10 of the CFTR gene, 1677delTA, which is very rare among CF chromosomes worldwide, was found to be a relatively common cause of cystic fibrosis in countries located in the region of the Black Sea. The frequency of the mutation was compared among cystic fibrosis patients from several populations, namely Bulgarians, Turks, Greek-Cypriots, Georgians, and Russians. The deletion is most common among Georgian CF patients and gradually declines in frequency in neighbouring populations. It is invariably related to a common polymorphic haplotype which is rare among normal chromosomes in Bulgaria but was found to be common in Turkey. The geographic gradient in the frequency of the mutation, along with findings on polymorphic haplotype distribution, suggest that the mutation is relatively young in evolutionary terms and spread as the result of west and south-bound migrations originating from Georgia. The 1677delTA mutation is related to a severe clinical phenotype with a high early mortality rate among homozygotes and possibly to an increased risk of meconium ileus.

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