Congenital insensitivity to pain with anhidrosis (CIPA; MIM 256800) is an autosomal-recessive disorder characterized by recurrent episodes of unexplained fever, anhidrosis (absence of sweating) and absence of reaction to noxious stimuli, self-mutilating behaviour and mental retardation. The genetic basis for CIPA is unknown. Nerve growth factor (NGF) induces neurite outgrowth and promotes survival of embryonic sensory and sympathetic neurons. Mice lacking the gene for TrkA, a receptor tyrosine kinase for NGF, share dramatic phenotypic features of CIPA, including loss of responses to painful stimuli, although anhidrosis is not apparent in these animals. We therefore considered the human TRKA homologue as a candidate for the CIPA gene. The mRNA and genomic DNA encoding TRKA were analysed in three unrelated CIPA patients who had consanguineous parents. We detected a deletion-, splice- and missense-mutation in the tyrosine kinase domain in these three patients. Our findings strongly suggest that defects in TRKA cause CIPA and that the NGF-TRKA system has a crucial role in the development and function of the nociceptive reception as well as establishment of thermoregulation via sweating in humans. These results also implicate genes encoding other TRK and neurotrophin family members as candidates for developmental defect(s) of the nervous system.

Although indirect, our data suggest the existence of a vascular isoform of podocin with a different molecular mass. We propose that examination of podocin expression may help differentiate MCD from FSGS.

The oculocerebrorenal syndrome of Lowe (OCRL) is an X-linked multisystem disorder with major abnormalities of eyes, nervous system, and kidneys. Clinical manifestations include congenital cataract, mental retardation, and renal tubular dysfunction. A gene (OCRL1) responsible for OCRL was identified by positional cloning and its product OCRL-1 protein was shown to be a phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] 5-phosphatase localized to the Golgi apparatus. We describe three mutations in OCRL1, one in a patient with severe phenotype and two in patients with moderate phenotype (degree of mental retardation and musculoskeletal abnormalities). The patient with severe phenotype had a G-to-A transition at nucleotide (nt) 1,739, causing an Arg-to-Gln substitution at amino acid 577, and one patient with moderate phenotype had a C-to-G transversion at nt 1,812, leading to a His-to-Gln substitution at amino acid 601. Both Arg-577 and His-601 are encoded by exon 15 and are probably important for proper function of this protein, since these are conserved in various enzymes catalyzing dephosphorylation of inositol compounds. In the other patient with the moderate phenotype, there was a G-to-A transition at nt 2,797 located at the 3'-end of exon 22. This substitution led to a skip of the same exon as well as conversion of codon-930 from GCT (Ala) to ACT (Thr) in the normal-size transcript. When we measured the enzyme activity in skin fibroblasts from the three patients, the activity was less than 10%, compared to findings in normal controls. Western blot analysis showed absence or severe decrease in OCRL-1 protein in cell lysates derived from these patients.

Familial idiopathic low-molecular-weight proteinuria (FILMWP) is a renal proximal tubulopathy that occurs predominantly in males. FILMWP is characterized by mild proteinuria consisting of low-molecular-weight proteinuria, aminoaciduria and relatively conserved renal function, but without rickets. To determine whether FILMWP is related to the CLCN5 gene, which is responsible for Dent's disease and two related disorders, we analyzed the CLCN5 gene from four Japanese families with FILMWP. We identified two novel mutations: one was a single base insertion at codon 520 serine in exon 10 and the other was a single base deletion at codon 403 tyrosine in exon 8. These mutations caused a shift in the reading frame, resulting in synthesis of truncated CLC5 proteins that lacked 220 (29%) and 314 (42%) amino acids, respectively. These mutations were demonstrated to cosegregate with the disease in two families, respectively. We conclude that the CLCN5 gene is responsible for this proximal renal tubulopathy in some Japanese families and that FILMWP is possibly a variant of Dent's disease.

We report four patients in a consanguineous family with focal segmental glomerulosclerosis (FSGS), early onset nephrotic syndrome, eventual end-stage renal failure, psychomotor retardation, seizures and microcephaly or brain atrophy without hiatus hernia. Other characteristic dysmorphic features were convergent strabismus and narrow forehead. One patient had enamel hypoplasia of the upper incisors and deviation of bilateral thumbs to palm side. We could not detect an NPHS2 mutation in this family. We propose that this may be another autosomal recessive syndrome with FSGS and neurological findings.