Alkaptonuria and Pompe disease in one patient: metabolic and molecular analysis

A review of the diverse genetic disorders in the Lebanese population: highlighting the urgency for community genetic services

The review lists the genetic diseases reported in Lebanese individuals, surveys genetic programs and services, and highlights the absence of basic genetic health services at the individual and community level. The incidence of individual diseases is not determined, yet the variety of genetic diseases reported is tremendous, most of which follow autosomal recessive inheritance reflecting the social norms in the population, including high rates of consanguinity, which favor the increase in incidence of these diseases. Genetic services including all activities for the diagnosis, care, and prevention of genetic diseases at community level are extremely inadequate. Services are limited to some clinical and laboratory diagnostic services with no genetic counseling. These services are localized within the capital thus preventing their accessibility to high-risk communities. Screening programs, which are at the core of public health prevention services, are minimal and not nationally mandated. The absence of adequate genetic services is attributed to many factors undermining the importance of genetic diseases and their burden on society, the most important of which is genetic illiteracy at all levels of the population, including high-risk families, the general public, and most importantly health care providers and public health officials. Thus, a country like Lebanon, where genetic diseases are expected to be highly prevalent, is in utmost need for community genetics services. Strategies need to be developed to familiarize public health officials and medical professionals with medical genetics leading to a public health infrastructure that delivers community genetics services for the prevention and care of genetic disorders at community level.

First report of a deletion encompassing an entire exon in the homogentisate 1,2-dioxygenase gene causing alkaptonuria

Alkaptonuria is often diagnosed clinically with episodes of dark urine, biochemically by the accumulation of peripheral homogentisic acid and molecularly by the presence of mutations in the homogentisate 1,2-dioxygenase gene (HGD). Alkaptonuria is invariably associated with HGD mutations, which consist of single nucleotide variants and small insertions/deletions. Surprisingly, the presence of deletions beyond a few nucleotides among over 150 reported deleterious mutations has not been described, raising the suspicion that this gene might be protected against the detrimental mechanisms of gene rearrangements. The quest for an HGD mutation in a proband with AKU revealed with a SNP array five large regions of homozygosity (5–16 Mb), one of which includes the HGD gene. A homozygous deletion of 649 bp deletion that encompasses the 72 nucleotides of exon 2 and surrounding DNA sequences in flanking introns of the HGD gene was unveiled in a proband with AKU. The nature of this deletion suggests that this in-frame deletion could generate a protein without exon 2. Thus, we modeled the tertiary structure of the mutant protein structure to determine the effect of exon 2 deletion. While the two β-pleated sheets encoded by exon 2 were missing in the mutant structure, other β-pleated sheets are largely unaffected by the deletion. However, nine novel α-helical coils substituted the eight coils present in the native HGD crystal structure. Thus, this deletion results in a deleterious enzyme, which is consistent with the proband’s phenotype. Screening for mutations in the HGD gene, particularly in the Middle East, ought to include this exon 2 deletion in order to determine its frequency and uncover its origin.