Adolescent idiopathic scoliosis (AIS) is one of the most common orthopedic disorders, affecting up to 4% of schoolchildren worldwide. We studied seven unrelated multiplex families of southern Chinese descent with AIS, consisting of 25 affected members. A genomewide scan with >400 fluorescent microsatellite markers was performed. Multipoint linkage analysis by GENEHUNTER revealed significant linkage of the abnormal phenotype to the distal short arm of chromosome 19, with both a maximum multipoint LOD score and a nonparametric LOD score of 4.93. Two-point linkage analysis by MLINK gave a LOD score of 3.63 (recombination fraction theta[m=f]=0.00) at D19S216. Further high-density mapping and informative recombinations defined the AIS critical region in the vicinity of D19S216, flanked by D19S894 and D19S1034, spanning 5.2 cM on the sex-averaged genetic map on chromosome 19p13.3.

A real time quantitative PCR (QPCR) method using TaqMan technology was used to assess the copy number of the two survival motor neuron genes (SMN1 and SMN2) on chromosome 5q13. This allows the accurate determination of carriers for spinal muscular atrophy (SMA), with one copy of SMN1. Analysis of 569 normal southern Chinese individuals revealed a carrier incidence of 1.6%, similar to that found in the western society. Study of 42 obligatory carriers showed a (2 + 0) genotype in two (4.8 %). In 27 SMA patients with homozygous deletion of the SMN1 gene, the number of SMN2 gene correlated with disease phenotype, with 68% of type II and III patients carrying three or more SMN2 genes, whilst the incidence of three or more SMN2 genes in the normal population was 1.57%.

Two multi-allelic microsatellite polymorphisms within the factor VIII gene were studied in 138 Chinese subjects. The allele sizes detected were higher than those found in Caucasian populations, whereas the heterozygosity rates were lower, being 0.5370 for intron 13 and 0.4444 for intron 22 repeats respectively. Their usefulness in diagnosis was compared to other intragenic and extragenic RFLPs, using previous data on the same 31 unrelated haemophilia A families. These intragenic microsatellite repeat polymorphisms were only informative for 18/31 families (58%); however, with the combined use of all existing RFLPs, the cumulative informativeness would be 100%.

The common restriction fragment length polymorphisms (RFLPs) associated with the FIX gene: 5' BamH I, Dde I, BamH I (2), Taq I and 3' Hha I were absent or of low incidence in Southern Chinese and are therefore not useful for linkage analysis. No deletion was detected amongst seven consecutive unrelated haemophilia B patients, but one had an insertion of a 15 kb Pvu II fragment containing exon d. Using an alternate strategy of polymerase chain reaction (PCR) amplification and direct sequencing, the molecular defect in the other six patients was defined. The four novel mutations characterized were: nucleotide (nt) 6410 G----C (Gly12----Ala); nt 31261 delta T (stop codon 31 bp downstream); nt 31260 C----G (Thr380----Ser) and nt 31122 C----A (Ala34----Asp). Two patients had the same mutation at nt 6365, G----A (Arg-4----Gln), identical to one previously described in other ethnic groups, suggesting that this is a hotspot for mutation. Each of the mutations was found to affect an enzyme recognition site and could thus be identified by direct visualization of abnormal restriction fragments in amplified genomic DNA. This allows rapid and accurate DNA diagnosis of haemophilia B in an ethnic group which otherwise shows little or no polymorphism for the common RFLP sites.