Autozygosity-driven genetic diagnosis in consanguineous families from Italy and the Greater Middle East.

Autozygosity-driven exome analysis has been shown effective for identification of genes underlying recessive diseases especially in countries of the so-called Greater Middle East (GME), where high consanguinity unravels the phenotypic effects of recessive alleles and large family sizes facilitate homozygosity mapping. In Italy, as in most European countries, consanguinity is estimated low. Nonetheless, consanguineous Italian families are not uncommon in publications of genetic findings and are often key to new associations of genes with rare diseases. We collected 52 patients from 47 consanguineous families with suspected recessive diseases, 29 originated in GME countries and 18 of Italian descent. We performed autozygosity-driven exome analysis by detecting long runs of homozygosity (ROHs > 1.5 Mb) and by prioritizing candidate clinical variants within. We identified a pathogenic synonymous variant that had been previously missed in NARS2 and we increased an initial high diagnostic rate (47%) to 55% by matchmaking our candidate genes and including in the analysis shorter ROHs that may also happen to be autozygous. GME and Italian families contributed to diagnostic yield comparably. We found no significant difference either in the extension of the autozygous genome, or in the distribution of candidate clinical variants between GME and Italian families, while we showed that the average autozygous genome was larger and the mean number of candidate clinical variants was significantly higher (p = 0.003) in mutation-positive than in mutation-negative individuals, suggesting that these features influence the likelihood that the disease is autozygosity-related. We highlight the utility of autozygosity-driven genomic analysis also in countries and/or communities, where consanguinity is not widespread cultural tradition.

Dissecting clinical findings: platelet defects segregate independently of deafness and cataract in a family affected by an apparent syndromic form of macrothrombocytopenia.

We studied a family with a suspected diagnosis of MYH9-related disease, which is one of the most common forms of autosomal dominant macrothrombocytopenias associated with hearing impairment, cataracts and nephritis. No mutation of the MYH9 gene was identified. Moreover, the A156V variant of the GPIbalpha gene, responsible for 30% of macrothrombocytopenias in Italy, was not detected in the family. Therefore, we hypothesized that the clinical symptoms were caused by mutations in different genes. The screening of the candidate genes for deafness and/or cataract allowed us to identify two variants, M34T and S19T, of the GJB2 gene in family members with hearing impairment. Because of the relatively common occurrence of inherited hearing loss and, at least in the Mediterranean area, of platelet macrocytosis, the two traits occurred by chance in the same family and mimicked the MYH9-related disease.

MYH9-related disease: May-Hegglin anomaly, Sebastian syndrome, Fechtner syndrome, and Epstein syndrome are not distinct entities but represent a variable expression of a single illness.

May-Hegglin anomaly, Sebastian syndrome, Fechtner syndrome, and Epstein syndrome are autosomal dominant macrothrombocytopenias distinguished by different combinations of clinical and laboratory signs, such as sensorineural hearing loss, cataract, nephritis, and polymorphonuclear Döhle-like bodies. Mutations in the MYH9 gene encoding for the nonmuscle myosin heavy chain IIA (NMMHC-IIA) have been identified in all these syndromes. To understand the role of the MYH9 mutations, we report the molecular defects in 12 new cases, which together with our previous works represent a cohort of 19 families. Since no genotype-phenotype correlation was established, we performed an accurate clinical and biochemical re-evaluation of patients. In addition to macrothrombocytopenia, an abnormal distribution of NMMHC-IIA within leukocytes was observed in all individuals, including those without Döhle-like bodies. Selective, high-tone hearing deficiency and cataract was diagnosed in 83% and 23%, respectively, of patients initially referred as having May-Hegglin anomaly or Sebastian syndrome. Kidney abnormalities, such as hematuria and proteinuria, affected not only patients referred as Fechtner syndrome and Epstein syndrome but also those referred as May-Hegglin anomaly and Sebastian syndrome. These findings allowed us to conclude that May-Hegglin anomaly, Sebastian syndrome, Fechtner syndrome, and Epstein syndrome are not distinct entities but rather a single disorder with a continuous clinical spectrum varying from mild macrothrombocytopenia with leukocyte inclusions to a severe form complicated by hearing loss, cataracts, and renal failure. For this new nosologic entity, we propose the term "MHY9-related disease," which better interprets the recent knowledge in this field and identifies all patients at risk of developing renal, hearing, or visual defects.

Genetics, clinical and pathological features of glomerulonephritis associated with mutations of nonmuscle myosin IIA (Fechtner syndrome).

BACKGROUND: Fechtner syndrome (FTNS), also known as Alport-like syndrome, is a rare inherited condition characterized by progressive nephritis, macrothrombocytopenia, Döhle-like leukocyte inclusions, deafness, and cataract. Although it recently was shown that FTNS derives from mutation of MYH9, the gene for the heavy chain of nonmuscle myosin IIA (NMMHC-IIA), its pathophysiological characteristics remain unknown. METHODS: We studied a large FTNS family in which 10 components carried a missense mutation of MYH9 determining the D1424H substitution. RESULTS: All affected subjects presented with macrothrombocytopenia and leukocyte Döhle-like bodies consisting of macroaggregates of NMMHC-IIA, but only two subjects had major renal problems characterized by proteinuria and renal failure. Electron microscopy showed focal and segmental effacement of podocytes and loss of the interpodocyte slit diaphragm. Immunohistochemistry showed apical localization of NMMHC-IIA in tubular epithelia and less podocyte staining in the two patients, whereas it was diffuse in normal epithelia. Three patients presented with stable microhematuria, and another five patients had no renal lesions, although they carried the same mutation of MYH9. Therefore, MYH9 mutation per se was responsible for platelet and leukocyte abnormalities, whereas additional predisposing conditions and/or environmental factors are necessary for nephropathy, cataract, and deafness. Looking at podocyte components conferring permselectivity properties to the kidney, we characterized the haplotype of podocin and found cosegregation of one specific allele in the two patients with nephrotic syndrome, suggesting a relationship between podocin features and proteinuria. CONCLUSION: Our study indicates a major role for the NMMHC-IIA abnormality in the pathogenesis of leukocyte, platelet, and kidney defects in FTNS. The basic feature in all cases is aggregation and compartmentation of NMMHC-IIA. However, proteinuria and podocyte lesions are the hallmark of nephropathy in patients who develop renal failure, and podocin may have some function in this setting.

Immunocytochemistry for the heavy chain of the non-muscle myosin IIA as a diagnostic tool for MYH9-related disorders.

May-Hegglin anomaly (MHA), Sebastian syndrome (SBS) and Fechtner syndrome (FTNS) are autosomal-dominant macrothrombocytopenias with Döhle-like leucocyte inclusions. These diseases are due to mutations of the MHY9 gene, encoding the heavy chain of non-muscle myosin IIA (NMMHC-A). We investigated the NMMHC-A localization in blood cells from eight MHA, SBS or FTNS patients with known MYH9 mutations. All the patients showed an altered localization of NMMHC-A in granulocytes and platelets, suggesting that Döhle-like bodies are due to the aggregation of NMMHC-A in the cytoplasm. Therefore, immunocytochemistry for NMMHC-A is a simple and sensitive method to detect pathological phenotypes of granulocytes and platelets in the diagnosis of MYH9-related disorders.